The decision could heighten the importance of the Values Voter Summit, to be headlined by James Dobson of Focus on the Family. Dobson has expressed doubts about several of the leading Republican contenders. But they nonetheless are planning to show up at the gathering because of the belief that evangelicals could hold the key to the GOP nomination.

Brownback's positions dovetail with those of the evangelical leaders, but he has failed to make headway because of the perception that he had little voter support. Brownback's withdrawal is expected to help former governor Mike Huckabee of Arkansas, who has a similar political philosophy and who has been "fishing from the same pool" for voters, according to Chuck Hurley, one of Brownback's closest friends and a key Iowa backer. Brownback is pulling out because "he doesn't have the name ID or connections . . . or money" that other candidates have, Hurley said in a telephone interview yesterday.

Meanwhile, Mitt Romney, a former governor of Massachusetts, could benefit indirectly because Brownback will no longer be on the debate stage as a vocal critic of Romney's switch to an antiabortion position.

Brownback had used some of his meager campaign resources to pay for automated phone calls to Iowa voters that portrayed Romney as being "proabortion" as recently as 2005. Romney called Brownback's attack "desperate" during an Aug. 5 debate, but Brownback defended the calls.

Romney, in his speech to the evangelical leaders tonight, does not plan to use the occasion to give a long-anticipated address about his Mormon faith, said spokesman Eric Fehrnstrom. "This is not a religion speech," he said.

Instead, the speech is expected to focus on Romney's proposals for strengthening families. The Romney campaign last night provided excerpts of the speech, quoting Romney as saying he is "pleased that so many people of many faiths have come to endorse my candidacy and my message."

The religious leaders hope to influence the campaign, but support among evangelicals is split widely among the top candidates and it is not clear that they will rally behind one candidate.

For example, while Rudy Giuliani has been criticized by evangelical leaders for his support of abortion rights, he leads Republicans among people who say they attend church weekly, with 27 percent support, followed by Fred Thompson at 24 percent and John McCain at 17 percent, according to a recent Gallup Poll. Romney came in fourth place among regular church-goers at 9 percent, followed by Huckabee at 7 percent.

This week, Romney won the endorsement of Bob Jones III, the chancellor of a fundamentalist Christian university in South Carolina that bears his family's name, but it was far from enthusiastic. "I'd rather endorse someone whose religion is wrong than somebody who doesn't have any religion at all," Jones said in announcing his support.

Romney yesterday said he wasn't bothered by the comment because he and Jones agree on many issues.

"We want marriage before babies," Romney said, according to the Associated Press. "We have the same things we want to fight for on issue after issue, so I'm happy to have his support."

Brownback, who hoped to be the evangelicals' candidate, has been stuck at 1 percent to 2 percent in national polls. During the third quarter of 2007, he raised about $925,000, less than his six GOP rivals, and had less than $95,000 in the bank by Sept. 30.

In a meeting with the Globe's editorial board earlier this week, Brownback was sober about his campaign standing, admitting "we've languished" since he finished third, behind Huckabee and Romney, in the Ames, Iowa, straw poll in August.

Brownback said his support for a guest-worker program for immigrants has hurt him among Republicans.

He also talked about trying to gain traction with his antiabortion views and by pushing a congressional apology for slavery. "If we can't, we won't be able to move forward," he said.

Brownback, who left his evangelical church four years ago and became a Catholic, had hoped to take advantage of concerns among some religious conservatives about some of his rivals.

Thus, Brownback found himself in a political Catch-22: Many evangelical leaders won't back him out of concern he has no chance, and he has little chance without strong support from evangelical leaders.

The Kansas City Star and Associated Press reported that Brownback will formally announce his withdrawal this afternoon in Topeka, and may indicate whether he plans to run for governor in 2010.

Thompson, who did not participate in two debates held since he formally entered the race last month, said the U.S. economy was not headed for a recession and warned against strict trade restrictions on China during the debate with his eight Republican rivals.

But he was a bystander in an early confrontation between Giuliani, former mayor of New York, and Romney, the former Massachusetts governor, who continued their running campaign-trail battle over tax and spending policies while in office.

Giuliani, who leads Republicans in national opinion polls in the November 2008 presidential race, said he brought taxes down 17 percent in New York while Romney let them increase by 11 percent in Massachusetts.

"The point is, you've got to control taxes. But I did it. He didn't," Giuliani said.

Romney shot back: "It's baloney. Mayor, you've got to check your facts. I did not increase taxes in Massachusetts. I lowered taxes."

Thompson and the other Republicans criticized the explosion of federal spending in recent years and said rising budgets and deficits under President George W. Bush had to be tamed. Arizona Sen. John McCain pointed to his own Republican Party as the culprit.

Representative John R. Kuhl Jr. of New York received just his second telephone call ever from his state's Democratic governor, Eliot Spitzer, last week and was not surprised at the topic: children's health insurance.

"He said, 'I am calling you to come over to the dark side,' " said Mr. Kuhl, who was urged by the governor to drop his opposition to health care legislation and join the effort to override President Bush's veto of the bill.

Mr. Kuhl, a Republican who narrowly survived the Democratic sweep of 2006, said he was unlikely to budge. As a result, voters in his district will also be getting calls - from Democrats and advocacy groups who are planning a telephone, radio, television and even text-message barrage against Republicans over what is shaping up as a defining domestic policy issue of the 2008 campaign.

Democrats believe they have Republicans - short on campaign cash, contending with a spurt of retirements and quarreling - on the run over the legislation, the State Children's Health Insurance Program. Party leaders say the willingness of so many House Republicans to stick with Mr. Bush in the face of bipartisan backing for a $35 billion expansion of the program to provide insurance for poor children will prove costly as Election Day looms a year from now.

"They know they cannot sustain this vote in the fall of 2008 and they are praying it gets worked out before then," said Representative Rahm Emanuel of Illinois, chairman of the House Democratic Caucus.

The Health and Human Services secretary, Michael O. Leavitt, said Sunday that Mr. Bush was ready to work it out. "The president has already said, 'I want a compromise,' " Mr. Leavitt said on the ABC program "This Week." But Democrats say that they have already compromised with Senate Republicans and they are in no hurry to scale back the plan.

Republicans acknowledge they could suffer some short-term damage from an issue easily framed as either favoring health care for poor children - or not.

"Certainly in the immediate, superficial look, everybody is for covering kids who don't have health insurance," said Representative Adam H. Putnam of Florida, chairman of the House Republican Conference.

But he and other Republicans say they eventually can turn the issue to their advantage by making the case that Democrats are spending too much, taking a first step toward national health care and devoting tax money to coverage for some families who can afford insurance. They contend their stance could have special resonance with conservatives unhappy with the recent Republican reluctance to resist popular spending programs.

"If this was October of next year, I'd be really worried," said Representative Roy Blunt of Missouri, the second-ranking House Republican. "But this is October of this year and the beginning of us getting our credibility back by showing that we are willing to take principled stands on spending."

House Republican leaders are confident they can hold their forces together and sustain the president's veto in a vote scheduled for Oct. 18. But over the next two weeks, Mr. Kuhl and more than two dozen other Republicans will face an onslaught of advertisements and public activities intended to put pressure on them to vote to override it.

The Democratic Congressional Campaign Committee is taking on eight Republicans in competitive districts with a series of automated calls and radio advertisements that remind listeners that their lawmaker gets taxpayer-paid health care while opposing the expansion of the program administered by each state.

Beginning Monday, a coalition of liberal and labor groups will start a $1 million advertising effort, with a national advertisement to run on cable channels and local advertisements aimed at specific lawmakers. The national commercial shows a series of children beginning with a baby girl and states, "George Bush just vetoed Abby." It says Mr. Bush puts excessive war spending over health care at home.

"The president's 'yes men' in Congress need to stand up to Bush and stand up for families who work hard but simply can't afford insurance," said Brad Woodhouse, president of Americans United for Change, one group leading the effort.

The health care fight is coming at an inopportune moment for Congressional Republicans. In the Senate, a string of retirements has created openings for Democrats to increase their slim majority. House Republicans have had retirements of their own and party fund-raising is lagging behind Democrats by a wide margin.

The Republican targets of the advocacy campaign say they do not view it as much of a threat, saying many of their voters will not consider the advertisements credible and that tactics like robocalls can backfire.

"I don't worry about it," said Representative Steve Chabot of Ohio, who noted that he strongly supported the insurance program when it was created in 1997. "I am perfectly satisfied with my vote and there is a range of reasons why I think this is a bad bill."

Bush volunteered his thoughts on a report on two secret 2005 memos that authorized extreme interrogation tactics against terror suspects. "This government does not torture people," the president said. Meanwhile, Senate Armed Services Committee Chairman Carl Levin, D-Mich., demanded a copy of a third Justice Department memo justifying military interrogations of terror suspects held outside the United States.

In a letter to Attorney General-nominee Michael Mukasey, Levin wrote that two years ago he requested - and was denied - the March 14, 2003, legal opinion. Levin asked if Mukasey would agree to release the opinion if the Senate confirms him as attorney general, and cited what he described as a history of the Justice Department stonewalling Congress.

Bush was referring to a report on two secret memos in 2005 that authorized extreme interrogation tactics against terror suspects. "This government does not torture people," the president said.

The two Justice Department legal opinions were disclosed in Thursday's editions of The New York Times, which reported that the first 2005 legal opinion authorized the use of head slaps, freezing temperatures and simulated drownings, known as waterboarding, while interrogating terror suspects, and was issued shortly after then-Attorney General Alberto Gonzales took over the Justice Department.

That secret opinion, which explicitly allowed using the painful methods in combination, came months after a December 2004 opinion in which the Justice Department publicly declared torture "abhorrent" and the administration seemed to back away from claiming authority for such practices.

A second Justice opinion was issued later in 2005, just as Congress was working on an anti-torture bill. That opinion declared that none of the CIA's interrogation practices would violate the rules in the legislation banning "cruel, inhuman and degrading" treatment of detainees, The Times said, citing interviews with unnamed current and former officials.

"We stick to U.S. law and international obligations," the president said, without taking questions afterward.

White House and Justice Department press officers have said the 2005 opinions did not reverse the 2004 policy.

Bush, speaking emphatically, noted that "highly trained professionals" conduct any questioning. "And by the way," he said, "we have gotten information from these high-value detainees that have helped protect you."

He also said that the techniques used by the United States "have been fully disclosed to appropriate members of the United States Congress" — an indirect slap at the torrent of criticism that has flowed from the Democratic-controlled Congress since the memos' disclosure.

"The American people expect their government to take action to protect them from further attack," Bush said. "And that's exactly what this government is doing. And that's exactly what we'll continue to do."

The 2005 opinions approved by Gonzales remain in effect despite efforts by Congress and the courts to limit interrogation practices used by the government in response to the Sept. 11, 2001, terrorist attacks. The authorizations came after the withdrawal of an earlier classified Justice opinion, issued in 2002, that had allowed certain aggressive interrogation practices so long as they stopped short of producing pain equivalent to experiencing organ failure or death. That controversial memo was withdrawn in June 2004.

The dispute may come down to how the Bush administration defines torture, or whether it allowed U.S. interrogators to interpret anti-torture laws beyond legal limits. CIA spokesman George Little said the agency sought guidance from the Bush administration and Congress to make sure its program to detain and interrogate terror suspects followed U.S. law.

Senate and House Democrats have demanded to see the memos.

"Why should the public have confidence that the program is either legal or in the best interests of the United States?" Senate Intelligence Committee Chairman Jay Rockefeller, D-W.Va., wrote in a letter to the acting attorney general.

House Judiciary Chairman John Conyers and Rep. Jerrold Nadler, D-N.Y., promised a congressional inquiry.

Sen. John McCain, R-Ariz., said he was "personally assured by administration officials that at least one of the techniques allegedly used in the past, waterboarding, was prohibited under the new law."

A White House spokesman, meanwhile, criticized the leak of such information to the news media and questioned the motivations of those who do so.

"It's troubling," Tony Fratto said Friday. "I've had the awful responsibility to have to work with The New York Times and other news organizations on stories that involve the release of classified information. And I can tell you that every time I've dealt with any of these stories, I have felt that we have chipped away at the safety and security of America with the publication of this kind of information."