Even if those proposals draw the 60 votes needed to overcome a Senate filibuster — a level that has eluded Democrats this year — any real strictures on the president would face a veto, frustrating war critics and raising the prospect that roughly as many American troops might be in Iraq a year from now as were there a year ago.

Still, the Democrats tried to get ahead of President Bush's planned speech on Iraq on Thursday night, and to press what they see as a political advantage in opposing the war in the months before the 2008 elections.

Senator Harry Reid of Nevada, the majority leader, and two party leaders on military issues accused Mr. Bush of embracing "more of the same" and of trying to pass off a routine troop reduction as a significant shift in policy.

"That is unacceptable to me, it is unacceptable to the American people," said Mr. Reid, who was flanked by Senators Carl Levin of Michigan, chairman of the Armed Services Committee, and Jack Reed of Rhode Island, a West Point graduate.

Democratic presidential contenders also assailed the administration's plan.

Senator Barack Obama of Illinois called for the withdrawal of one or two combat brigades a month, starting immediately.

Senator Hillary Rodham Clinton of New York said taking credit for the force reductions that Gen. David H. Petraeus, the commander in Iraq, was recommending, and that Mr. Bush appeared ready to accept, was "like taking credit for the sun coming up in the morning."

With Democrats intensifying their attacks on the strategy outlined this week by General Petraeus, the administration is setting in motion its plans with a prime-time speech by the president on Thursday, a subsequent visit to a military base and continued appearances by General Petraeus and Ryan C. Crocker, the American ambassador in Baghdad.

At a news conference on Wednesday, General Petraeus reiterated that he was unwilling to commit to troop cuts beyond a five-brigade reduction by mid-July, a level he described as prudent. There are 20 combat brigades in Iraq.

He also took issue with claims that such a reduction would not be significantly faster than what had already been scheduled. Combat forces in Iraq serve up to 15-month tours. Under that limit, part of the Pentagon's broad effort to lessen the strains on the military, General Petraeus would not have had to pull out any combat units until April, instead of removing the first brigades in mid-December, he said.

"We are coming out quicker than we had to," he said.

The White House spokesman, Tony Snow, in his last news briefing before leaving the job, rejected Democrats' complaints that the administration's plan was simply a return to the level that existed before more than 30,000 additional troops were sent into Iraq this year, a buildup that the administration pointedly referred to as a surge, suggesting its temporary nature.

"It's a different country," said Mr. Snow of Iraq. "You have the ability to reduce the numbers because there have been changes that reduced the necessity of American involvement."

Senator Reid would not provide details of the legislative proposals that Democrats will pursue. But Mr. Levin and Mr. Reed have been working with some Republicans on a measure that would focus the military mission on counterterrorism, training Iraqis and protecting forces already there — a switch intended to allow large numbers of combat troops to be withdrawn by next spring.

"We have to go ahead and recognize the strain on the military forces and give them the tasks that they can do so well," said Mr. Reed, a former Army captain, "but within the capability of their resources and the best interests of the United States."

They have been exploring the idea of making the withdrawal more of an objective than a requirement in order to attract Republican votes, but that approach could cause defections by Democrats.

Democrats have been picking up new Republican support for a measure that requires troops to spend at least the same amount of time at their home bases as they did in Iraq before returning — a requirement that could reduce troop numbers because the Pentagon would not have as many eligible for deployment.

"I think that might be a good way to accelerate a troop reduction," said Senator Gordon Smith, Republican of Oregon, who noted that it was also popular with strained military families.

That measure attracted 56 votes this summer, and some Republicans who opposed it then, including George V. Voinovich, Republican of Ohio, have expressed new interest. Senator Arlen Specter, Republican of Pennsylvania, said Wednesday that he was considering the proposal, and Democrats were also trying to persuade Senator Lisa Murkowski, Republican of Alaska.

Mr. Reid said Democrats also planned to vote on more aggressive legislative challenges to the war, which could help appease critics who are demanding that Democrats take tougher action.

Democrats say they may also be more willing to try to attach conditions to coming Pentagon spending requests. (Democrats have been reluctant to limit money for the war unilaterally.) "I think the American people are getting tired of sending the money with no end in sight," said Senator Charles E. Schumer, Democrat of New York.

The struggle to settle on a party alternative illustrates the problems Democrats are having finding a way to take on the president that unites their party and avoids criticism that they are weak on national security.

As Democrats huddled Wednesday to prepare for the floor debate, a group of leading House Republicans arrived in Iraq to demonstrate their backing for the president. The lawmakers, led by Representative John A. Boehner of Ohio, the Republican leader, had been in Iraq less than five hours, but in a conference call with reporters they said their initial briefings had already confirmed improvements.

"Clearly what's happened over the last three months has been real success," said Mr. Boehner, who previously visited Iraq in July 2006.

In an interview on "The Today Show" on Wednesday, Secretary of State Condoleezza Rice said stabilizing Iraq was part of "a long process of dealing with what the president called a long time ago a generational challenge to our security brought on by extremism, coming principally out of the Middle East."

Speaker of the House Nancy Pelosi, a California Democrat, said Ms. Rice's comment represented an acknowledgment that the United States would be engaged in Iraq for "years to come."

"We need a new direction that redeploys our troops from Iraq, rebuilds our military and refocuses on fighting terrorism across the world," Ms. Pelosi said.

The proposed withdrawal would reduce the number of U.S. troops in Iraq to about 130,000 - the same as before the "surge" earlier this year aimed at reducing sectarian violence.

Congressional Democratic leaders criticized Mr. Bush's plan after a meeting with the president Tuesday. House Speaker Nancy Pelosi said it was "an insult to the intelligence of the American people."

General Petraeus and Ryan Crocker, the U.S. ambassador to Iraq, testified before House and Senate committees earlier this week. General Petraeus says the troop increase has led to decreased violence in Iraq, but he and Crocker cautioned against a premature withdrawal of U.S. forces from Iraq.

Iraq's national security advisor, Muwaffaq al-Rubaie, told reporters Wednesday that the number of U.S. troops could be reduced to 100,000 by the end of 2008. He says it would depend on the security threat within and outside the country, and the readiness level of Iraqi security forces.

Starting today, Thompson will spend the next week in the key early primary states of Iowa, New Hampshire, South Carolina and Florida.

He's betting he can make up for lost time and convince skeptics in his party that he's neither lazy nor underprepared, but instead methodical and getting in just as voters are ready to pay attention. All of his major competitors have spent months courting voters, raising money and refining their stances.

"He could catch fire and take off," said Cary Covington, an associate professor of political science at the University of Iowa. "But, historically, candidates who rely in Iowa on television ads and commercials don't do well. It takes organizing at the grassroots level and that takes time, and Thompson just doesn't have much of that time left now. He can't afford any mistakes. He has to hit hard and charge hard and really be running full blast."

Thompson has strengths going in. He's got celebrity and a homespun appeal as well as experience in national politics. He's also got a socially conservative message and reputation that could appeal to his party's base.

So far, Republicans have yet to solidify around any single competitor, be it former New York Mayor Rudy Giuliani, former Massachusetts Gov. Mitt Romney or any of the others.

Recent polls in early primary states show Thompson in second or third place among GOP candidates, in some combination with Giuliani and Romney.

Yet with his announcement, Thompson is off to mixed reviews.

Thompson's timing allowed him to avoid participating, literally by a few hours, in a televised Wednesday night candidate debate in New Hampshire. But his campaign bought time on Fox to air a 30-second Thompson spot during the debate.

That prompted New Hampshire's Republican Party chairman to accuse Thompson of wanting it both ways.

"I think New Hampshire voters and voters elsewhere would be forgiven for thinking he's skipping the debate because he isn't ready to have a substantive debate on the issues," chairman Fergus Cullen said. "And voters also could be forgiven for thinking, 'Well, what the heck was he doing all summer if he wasn't preparing?' There's a genuine interest here in Sen. Thompson and curiosity. But he seems to be getting off on the wrong foot."

Thompson's communications director Todd Harris defended the strategy. "We're not skipping debates," Harris said. "We're going to be present at a number of debates" in New Hampshire and other states in the weeks and months ahead.

"It's a question of how we've decided to roll out our campaign. And this is how we've decided to do it.

"Jay Leno is one of the highest-rated shows on television, and Sen. Thompson's message is going to be about bringing the country together under a banner of mainstream conservative change," Harris said. "You can't talk about unifying the country without talking to the entire country."

Harris describes Thompson as "the best communicator of the mainstream conservative message" in the GOP. "And our party needs a good communicator at a time when many in the public are not as high on the Republican Party as they used to be," he said.

An unbroken line of precedents dating back 220 years makes clear the Senate does not consider misdemeanor private conduct to be a fit subject of inquiry, asserted Washington attorney Stan Brand.

"We ought to seek to have the committee dismiss this outright," Brand said of a Senate ethics panel's investigation. "The Republican leadership called for an ethics investigation that had nothing to do with his office," said Brand on NBC's "Today" show.

Craig says he may still fight for his Senate seat, a spokesman says — if the lawmaker can clear his name with the Senate ethics panel and a Minnesota court.

The Republican lawmaker, who has represented Idaho for 27 years, announced Saturday that he intended to resign.

"It's not such a foregone conclusion anymore that the only thing he could do was resign," Sidney Smith, Craig's spokesman in Idaho's capital, told The Associated Press on Tuesday.

Mr. Bush’s visit to Iraq — his third — was spent at this remote desert base in the restive Sunni province of Anbar, where he had summoned Iraq’s Shiite prime minister, Nuri Kamal al-Maliki, and others to demonstrate that reconciliation among Iraq’s warring sectarian factions was at least conceivable, if not yet a fact.

After talks with Gen. David H. Petraeus, the top American commander in Iraq, and Ryan C. Crocker, the ambassador to Iraq, Mr. Bush said that they “tell me that if the kind of success we are now seeing here continues it will be possible to maintain the same level of security with fewer American forces.”

Mr. Bush did not say how large a troop withdrawal was possible. Nor did he say whether he envisioned any forces being withdrawn sooner than next spring, when the first of the additional 30,000 troops Mr. Bush sent to Iraq this year are scheduled to come home anyway.

Still, his remarks were the clearest indication yet that a reduction would begin sometime in the months ahead, answering the growing opposition in Washington to an unpopular war while at the same time trying to argue that any change in strategy was not a failure.

“Those decisions will be based on a calm assessment by our military commanders on the conditions on the ground — not a nervous reaction by Washington politicians to poll results in the media,” Mr. Bush told a gathering of American troops, who responded with a rousing cheer. “In other words, when we begin to draw down troops from Iraq, it will be from a position of strength and success, not from a position of fear and failure. To do otherwise would embolden our enemies and make it more likely that they would attack us at home.”

To ensure security, the White House shrouded Mr. Bush’s visit to Iraq in secrecy.

Mr. Bush flew with Secretary of State Condoleezza Rice and his national security adviser, Stephen J. Hadley, an extraordinary gathering of top leaders in a war zone. Defense Secretary Robert M. Gates and Gen. Peter Pace, the chairman of the Joint Chiefs of Staff, flew to Iraq separately and joined them.

The Anbar region is a Sunni stronghold where in recent months there have been significant improvements in security. Administration officials have been touting the gains as evidence that the increase in American troops has proved a success — a word Mr. Bush used eight times in his public remarks on Monday.

Mr. Hadley, briefing reporters, recalled a military intelligence officer’s dire warning a year ago that Al Qaeda controlled the provincial capital, Ramadi, and other towns in the region. “Anbar Province is lost,” he quoted the analyst as saying then. Mr. Hadley was apparently referring to Al Qaeda in Mesopotamia, the homegrown Sunni Arab extremist group that American intelligence agencies have concluded is foreign led. The extent of its links to Osama bin Laden’s network is not clear.

On Monday, after meeting with some of the local Sunni leaders who only months ago led the struggle against the American presence in the region, Mr. Bush held up Anbar as a model of the progress that was possible.

“When you stand on the ground here in Anbar and hear from the people who live here, you can see what the future of Iraq can look like,” he said, night having fallen at the base.

During his visit, Mr. Bush did not leave the base, a heavily fortified home to about 10,000 American troops about 120 miles west of Baghdad. Mr. Hadley said planning for the trip had started five or six weeks ago.

Administration officials rejected the notion that the trip was a publicity stunt. They said Mr. Bush wanted to meet face-to-face with General Petraeus and Mr. Crocker, who are to testify before Congress about progress in Iraq next week, and with Iraqi leaders he has been pressing from afar to take steps toward political reconciliation.

By summoning Mr. Maliki and other top officials to the Sunni heartland, a region the Shiite prime minister has rarely visited, Mr. Bush succeeded in forcing a public display of unity. The Iraqi officials there included President Jalal Talabani, Vice President Adel Abdul-Mehdi, Vice President Tariq al-Hashemi, Deputy Prime Minister Barham Salih and Massoud Barzani, the president of the Kurdistan region.

Iraq’s foreign minister, Hoshyar Zebari, who was visiting neighboring Iran when Mr. Bush and the other top administration officials arrived, was conspicuously absent. Mr. Zebari, a Kurd, said he had been aware that high-level visitors from the United States were coming but that his trip to Iran had been planned long in advance and that the timing was strictly a coincidence.

In Washington, a spokesman for Senator Harry Reid of Nevada, the Democratic majority leader, said the president’s visit and his assertions about progress would do little to persuade skeptics. “Despite this massive P.R. operation, the American people are still demanding a new strategy,” the spokesman, Jim Manley, said in a telephone interview.

Anthony H. Cordesman, a senior fellow at the Center for Strategic and International Studies, said the reversal in Anbar had less to do with American strategy than with local frustration over the extremism of Al Qaeda fighters trying to impose their doctrine. Mr. Cordesman suggested it was more of an anomaly than a model that could be applied elsewhere in Iraq, where sectarian divisions and strife appear to be worsening.

“We are spinning events that don’t really reflect the reality on the ground,” he said.

While some administration officials have recently described the Sunni shift in Anbar as serendipitous, they portrayed the improvements as an outgrowth, at least in part, of the decision to send nearly 4,000 additional marines to the province as part of the White House strategy to increase troops. “This is not serendipity,” Mr. Hadley told reporters.

Distrust remains deep between Sunnis in Anbar and the Maliki government — and it is clear that Mr. Maliki sees efforts by the American military to organize armed groups of Sunnis to assist American troops as a policy that amounts to assisting his enemies. Nor is it clear that the same model can be made to work in areas of Iraq where Sunnis and Shiites live together.

Sunnis, for their part, complain that the Maliki government has long failed to deliver services and to share oil revenue with Anbar. Describing the meeting Monday between the tribal sheiks and Iraqi officials from Baghdad, Mr. Gates said, “There was a sense of shared purpose among them and some good-natured jousting over resources.”

It remained unclear whether Mr. Bush planned to announce any specific troop withdrawals when he delivers the congressionally mandated report later this month.

Several administration officials say Mr. Bush and his commanders and military advisers have neared a consensus on beginning a reduction in American forces. Speaking to reporters traveling with him, Mr. Gates said Monday that he had formulated his opinion, though he declined to disclose it.

Asked about Mr. Bush’s comments on possible troop reductions, Mr. Gates added, “Clearly that is one of the central issues that everyone has been examining — what is the security situation, what do we expect the security situation to be in the months ahead?” He went on to say, “What opportunities does that provide in terms of maintaining the security situation while perhaps beginning to bring the troop level down?”

As he did in Washington late last week, Mr. Bush urged lawmakers to withhold judgment on the situation in Iraq until hearing first-hand reports next week from General Petraeus and Mr. Crocker. At the same time, though, he has used the White House’s considerable platform to assert his own views.

“The strategy we put into place earlier this year was designed to help the Iraqis improve their security so that political and economic progress could follow,” Mr. Bush said after meeting with Mr. Maliki and the other Iraqi leaders. “And that is exactly the effect it is having in places like Anbar.”

On Monday, at a news conference in Baghdad, Mr. Maliki made his own effort to underscore political progress his government had achieved in recent weeks. He said that a long-discussed law allowing former members of the Baath Party of Saddam Hussein to return to jobs in government had been submitted to Parliament.

“This law has been approved by the political leaders, and by the national political council,” Mr. Maliki said. “It is now before the parliament to discuss it and approve it.”

Agreement on the law, part of a package of requirements pressed by the Bush administration, would be an important milestone.

“We believe that this law represents the minimum accepted level of our ambitions,” said Salman al-Jumaili, a lawmaker from the main Sunni coalition.

An earlier agreement on a law broke down after Shiite leaders in southern Iraq voiced opposition.

Although no reason was given, Snow recently told conservative radio talk show host Hugh Hewitt that, due to financial reasons, he did not expect to remain on the White House staff through the remainder of President Bush's term.

Bush told reporters Friday that he will "sadly accept" Snow's resignation.

Flanked by Snow and Perino in the White House press room, the president spoke warmly of his departing press secretary.

"It's been a joy to watch him spar with you," Bush told reporters.

Bush said he was certain of two things in regard to Snow.

"He'll battle cancer and win," Bush said, "and he'll be a solid contributor to society."

Turning to Snow, the president then said: "I love you, and I wish you all the best."

Taking the podium, Snow said he was thankful for the opportunity to serve as press secretary.

"This job has been a dream for me -- and a blast," Snow said.

Snow's cancer was diagnosed for the first time in February 2005. His colon was removed, and after six months of treatment, doctors said the cancer was in remission.

Perino announced March 27 that Snow's cancer had recurred, and that doctors had removed a growth from his abdomen the day before.

Sources told CNN two weeks ago that Snow was planning to leave his job, possibly as early as September.

Snow, who had said he would leave his post before the end of Bush's second term, repeated that the decision is based on finances, not health. He took a major pay cut after leaving the world of cable television and talk radio to come to the White House.

According to The Washington Post, Snow makes $168,000 as the White House spokesman.

Bush tapped Snow to replace Scott McClellan in April 2006. Snow had been an anchor for "Fox News Sunday" and a political analyst for the Fox News Channel, which he joined in 1996. He also hosted "The Tony Snow Show" on Fox News Radio.

On Thursday, Snow told CNN his health is improving, citing two new medical tests this month which found the cancer has not spread.

"The tumors are stable -- they are not growing," Snow said of the results from an MRI and a CAT Scan. "And there are no new growths. The health is good."

The press secretary, whose hair has turned gray during chemotherapy treatment, said his black hair is expected to grow back in about a month.

"I'm also putting on weight again," he said after returning from a 10-day vacation. "I actually feel very good about" the health situation.

Snow said that on Friday he was to see his oncologist, and they will decide on some minor forms of chemotherapy to start as maintenance treatment.