They dispatched the letter shortly before Sen. Patrick Leahy, D-Vt., announced the subpoena of Rove, the president's top political strategist, in remarks on the Senate floor. The White House has claimed executive privilege to block Congress from receiving documents or testimony by current and former presidential aides.

``We have now reached a point where the accumulated evidence shows that political considerations factored into the unprecedented firing of at least nine United States attorneys last year,'' said Leahy, chairman of the Senate Judiciary Committee.

In response, White House spokesman Tony Fratto said, "Every day congressional Democrats prove that they're more interested in headlines than doing the business Americans want them to do. And Americans are now taking notice that this Congress, under Democratic leadership, is failing to tackle important issues," he said.

Gonzales is at the center of the U.S. attorney controversy, but the call for a perjury probe involved alleged conflicts between testimony he gave the Judiciary Committee in two appearances, one last year and the other this week. The issue revolves around whether there was internal administration dissent over the president's warrantless wiretapping program.

As for the firing of the prosecutors, e-mails released by the Justice Department show Gonzales' aides conferred with Rove on the matter.

Leahy also said he was issuing a subpoena for J. Scott Jennings, a White House political aide. The deadline for him and Rove to comply was set as Aug. 2.

"For over four months, I have exhausted every avenue seeking the voluntary cooperation of Karl Rove and J. Scott Jennings, but to no avail," the Vermont lawmaker said. "They and the White House have stonewalled every request. Indeed, the White House is choosing to withhold documents and is instructing witnesses who are former officials to refuse to answer questions and provide relevant information and documents."

The call for a perjury investigation marked yet another complication for Gonzales, whose fitness to serve has been bluntly criticized by Republicans and Democrats alike.

Sen. Arlen Specter, R-Pa., the senior Republican on the Senate Judiciary Committee, told reporters aboard Air Force One during the day that he "might" raise the issue with the president, who has steadfastly stood by his longtime friend.

And Senate Majority Leader Harry Reid, D-Nev., told reporters, "I'm convinced that he's not telling the truth," based on conversations with Democrats on the Judiciary Committee.

In a separate letter Thursday to Gonzales, Leahy said he would give the attorney general eight days to correct, clarify or otherwise change his testimony "so that, consistent with your oath, they are the whole truth."

In their letter to Clement, the four senators wrote that Gonzales' testimony last year that there had been no internal dissent over the president's warrantless wiretapping program conflicted with testimony by former Deputy Attorney General James Comey and with Gonzales' own statements this week before the Judiciary Committee.

They also said Gonzales falsely told the panel that he had not talked about the firings with other Justice Department officials. His former White House liaison, Monica Goodling, told the House Judiciary Committee under a grant of immunity that she had an "uncomfortable" conversation with Gonzales in which he outlined his recollection of what happened and asked her for her reaction.

"The attorney general should be held to the highest ethical standards," the senators wrote.

Sen. Charles Schumer, D-N.Y., one of the four lawmakers to sign the letter, was sharply critical of Gonzales. "There's no wiggle room." Schumer said.
It's not misleading. Those are deceiving. Those are lying."

Clement would decide whether to appoint a special prosecutor because Gonzales and outgoing Deputy Attorney General Paul McNulty have recused themselves from the investigation that involves them. The Justice Department's No. 3 official, Associate Attorney General William Mercer, is serving only in an acting capacity and therefore does not have the authority to do so.

At issue is what was discussed at a March 10, 2004, congressional briefing. A letter from then-Director of National Intelligence John Negroponte said the briefing concerned the administration's terrorist surveillance program on the eve of its expiration.

But Gonzales, at Tuesday's Senate Judiciary Committee hearing, repeatedly testified that the issue at hand was not about the terrorist surveillance program, which allowed the National Security Agency to eavesdrop on suspects in the United States without receiving prior court approval.

Instead, Gonzales said, the emergency meetings on March 10, 2004, focused on an intelligence program that he would not describe. He said the meeting prompted him to go to the bedside of ailing then-Attorney General John Ashcroft to recertify the surveillance program, but he denied pressuring Ashcroft to do so. Ashcroft, recovering from gall bladder surgery, refused.

White House press secretary Tony Snow defended Gonzales on Thursday but would not talk about the subject of the 2004 briefing.

"Unfortunately we get into areas that you cannot discuss openly," Snow said. "It's a very complex issue. But the attorney general was speaking consistently. The president supports him. I think at some point this is going to be something where members are going to have to go behind closed doors and have a fuller discussion of the issues. But I can't go any further than that."

The trickle of Republican rebellion against President George W.Bush's Iraq policy has turned into a stream with two more previously loyal senators joining the swelling ranks ofcritics.

Lamar Alexander said "it should be clear to the President that there needs to be a new strategy", while Judd Gregg called for a "clear blueprint for how we were going to draw down".

Although they stopped short of backing the Democratic proposals for a fixed timetable of withdrawing US troops from Iraq, their comments came before a week in which the Senate is once again debating funding for the war and the military will deliver an interim progress report on Mr Bush's "surge strategy".

The interim report is believed to conclude that US combat deaths have escalated, violence has spread beyond Baghdad and sectarianism has further polarised Iraq, the Washington Post has reported.

It is also expected to acknowledge tacitly that the Iraqi Government is unlikely to meet any of the political and security goals Mr Bush set for it in January.

"The security progress we're making in Iraq is real," a senior intelligence official in Baghdad was quoted as saying, "but it's only in part of the country and there's not enough political progress to get us over the line in September."

Six Republican senators have now announced they can no longer support Mr Bush's Iraq strategy, and demanded change.

The dissent has been led by senior figures including Richard Lugar and John Warner, the Republican leaders - or "ranking members" - on the Senate foreign and armed forces committees.

Senator Lugar yesterday used a TV interview to explain that his public intervention had been intended as a "reaching-out to the President".

He suggested that remaining opportunities for a centrist "bipartisan consensus" on Iraq were fast disappearing before presidential elections next year in which Democrats are being pushed by activists to call for an immediate withdrawal of troops.

Along with other Republicans who have spoken out in recent days, such as George Voinovich and Pete Domenici, Senator Lugar appears to be advocating measures similar to those of last year's Iraq Study Group report.

That report proposed shifting American troops away from the sectarian conflict between Sunnis and Shi'ites so that a reduced force could concentrate on counter-terrorism and support functions.

"We have to be thoughtful about the safest route for our forces out of Iraq," Senator Lugar said, adding that most ofthe 160,000 US troops stationed in the country could be "redeployed by the middle part of next year".

Moderate Republicans fear that Mr Bush's apparent determination to fight on will lead to a panic pullout that could set off awider conflict across the MiddleEast.

But the White House is urging them to hold the line at least until September, when General David Petraeus will present his assessment of the effectiveness of the 30,000-troop "surge".

Mr Bush has repeatedly said he wants as much time as possible for his 30,000-troop increase to show results.

But the American military is already overstretched, with the Pentagon making troops serve longer in battle zones - and more often - as it tries to sustain the surge.

There is now growing pressure on Mr Bush to pre-empt the September report by setting out a time frame for withdrawing at least some of the troops.

Some Bush aides believe forces are combining against him as the Senate prepares to begin a contentious debate on the defence authorisation bill.

Democrats are gearing up for a new push for a US exit from Iraq amid a surge in bloodshed at the weekend.

With public discontent with the war growing, house Speaker Nancy Pelosi is set to introduce a bill to authorise troop redeployments to start within four months and be completed by April, a formula Mr Bush has blocked once with a presidential veto.

But aides are now believed to be advising Mr Bush that if he wants to forestall more defections, it would be wiser to announce plans for a more narrowly defined mission for US troops that would allow for a staged pullback, The New York Times reported yesterday.

The number of US combat brigades in Iraq is, in any case, scheduled to be reduced from 20 to 15 by this time next year.

Meanwhile, US military sources in Baghdad said fiery Iraqi Shia cleric Moqtada al-Sadr, head of the the Mahdi Army militia insurgency group, has gone back to Iran. Sadr led two uprisings against US forces in 2004 before becoming more involved in mainstream politics.

Rep. Jim McDermott said Friday he will ask the Supreme Court to decide whether he had a right to disclose contents of an illegally taped telephone call involving House Republican leaders a decade ago.

A federal appeals court ruled in May that the Washington state Democrat should not have given reporters access to the tape-recorded telephone call of Republican leaders discussing the House ethics case against former House Speaker Newt Gingrich, R-Ga.

McDermott's offense was especially egregious since he was a senior member of the House ethics committee, the U.S. Circuit Court of Appeals for the District of Columbia said in a 5-4 ruling.

The congressman called the ruling an infringement of his free speech rights.

"With all due respect to the Court of Appeals, the constitutional issues involved here are much too important to be confused by a split decision," he said in a statement Friday.

"The protections afforded all Americans by the First Amendment have been placed on a very slippery slope by this (appeals court) decision," McDermott said, adding that the May 1 ruling "endangers freedom of speech and the press across America."

In its ruling, the appeals court said that when McDermott became a member of the House ethics panel, he "voluntarily accepted a duty of confidentiality" and therefore had no First Amendment right to disclose the tape to journalists.

The ruling upheld a previous decision ordering McDermott to pay House Minority Leader John Boehner, R-Ohio, more than $700,000 for leaking the taped conversation. The figure includes $60,000 in damages and more than $600,000 in legal costs.

Boehner was among several GOP leaders heard on the December 1996 call, which involved ethics allegations against Gingrich. Then the House speaker, Gingrich was heard on the call telling Boehner and others how to react to allegations. He was later fined $300,000 and reprimanded by the House.

McDermott, who was then serving on the ethics panel, leaked the tape to two newspapers, which published stories on the case in January 1997.

In a sharp dissent, Judge David B. Sentelle said that under the majority's ruling, "no one in the United States could communicate on this topic of public interest because of the defect in the chain of title," that is, the fact that the tape was obtained illegally.

"I had to make a very difficult decision," Bush said at a brief meeting with reporters after visiting wounded troops at Walter Reed Army Medical Center. "I felt like the jury verdict ought to stand, and I felt like some of the punishments that the judge determined were adequate should stand. But I felt like the 30-month sentencing was severe."

Bush's commutation wiped out Libby's 30-month prison sentence, but left intact his criminal conviction, a $250,000 fine, and the two years of probation Libby must serve. With some Republicans calling for a full pardon and many Democrats condemning Bush's action, the president said he does not regret making the controversial decision.

"I made a judgment, a considered judgment, that I believe was the right decision to make in this case," the president said. "And I stand by it."

While the commutation continued to generate heated debate yesterday, it also served as a reminder that presidents from both parties have made controversial decisions to grant clemency. Conservatives defending the Libby commutation point to President Clinton's 11th-hour pardon of billionaire fugitive Marc Rich. On his last day in office, Clinton granted clemency to Rich, who faced prison time for tax evasion; his former wife, Denise, contributed $70,000 to a fund supporting Hillary Clinton's Senate bid.

Senator Clinton, a contender for the Democratic presidential nomination, issued a stinging rebuke of Bush's commutation of Libby's sentence. Leniency for Libby "sends the clear signal that in this administration, cronyism and ideology trump competence and justice," she said in a statement issued Monday.

Clinton, however, is continuing to deal with the fallout of her husband's decision to pardon a Tennessee couple who were represented by her brother, Anthony Rodham, who has said he talked to President Clinton about the pardons.

A US Bankruptcy Court in Nashville is slated next week to hear arguments that Rodham should pay more than $100,000 to the couple's estate; at issue is whether Rodham received the money as salary or as a loan that must be repaid. It is possible that Anthony Rodham could be called to testify about the matter, reviving questions about the role of Hillary and Bill Clinton in the pardon.

Lawyers for both sides in the case said they are in negotiations this week that could lead to a settlement.

Another of Senator Clinton's brothers, Hugh Rodham, represented two clients who received a pardon and a sentence commutation from President Clinton.

Her brothers' involvement in cases related to pardons and commutations her husband issued was an embarrassment to Senator Clinton during her first Senate bid and could resurface as she seeks the Democratic presidential nomination. She has denied playing a role in the clemency decisions.

Phil Singer, a spokesman for Clinton's presidential campaign, said there is no comparison between the Clinton pardons and Bush's grant of clemency to Libby. "What sets this incident apart," he said, "is the administration politicizing national security in an effort to intimidate its critics."

Libby, a White House insider and chief proponent of the Iraq invasion, was convicted of perjury and obstruction of justice for lying to a grand jury and authorities as they tried to determine who leaked the name of a CIA operative -- part of a White House effort to undercut criticism of Bush's decision to go to war against Iraq.

After a federal judge sentenced him, Libby asked to remain free on bail while his case is on appeal. On Monday, a federal appellate court rejected that request, but Bush's commutation spared Libby any time behind bars.

At a press briefing yesterday, reporters asked White House spokesman Tony Snow whether Cheney -- who calls Libby a friend and who has enormous influence within the White House -- had pressed for Bush to commute Libby's sentence.

"I don't have direct knowledge," Snow said. "But on the other hand, the president did consult with most senior officials, and I'm sure that everybody had an opportunity to share their views."

A Justice Department spokesman said the Libby commutation is the only instance in which the president did not rely on a review from the Office of the Pardon Attorney. Bush issued 113 pardons but just three commutations of sentence before the Libby action, according to Justice Department officials.

Snow said Bush did not ask for a review of the case because, "It's not like people's memories are fuzzy about the details or the circumstances."

Bush has issued far fewer pardons and commutations than Clinton to date, although presidents tend to grant clemencies in bunches in their waning days in office. President George H. W. Bush, George Bush's father, granted 74 pardons and three sentence commutations during his four-year term, while President Clinton granted 396 pardons, 61 sentence commutations, and two remissions of fines during his two terms in office, according to federal records.

Both issued a number of controversial pardons: Besides pardoning Rich, the fugitive financier, Clinton pardoned his brother, Roger, who was charged with conspiracy to distribute cocaine, while the elder Bush pardoned his former secretary of defense, Caspar Weinberger, of charges related to the Iran-contra affair.

Margaret Love, the Justice Department's pardon attorney under both the elder Bush and Clinton, said that the current President Bush has used his clemency power sparingly. Of the more than 5,500 commutation requests Bush has received, Love said, he has denied 4,108 of them, left more than 1,000 cases pending, and granted just four cases -- including Libby's.

Similarly, Bush has received 1,399 pardon requests, denying 1,022 and granting 113.

Though she is "agnostic" about the merits of Libby's case, Love said she represents a number of individuals seeking clemency and hopes the Libby action is a positive sign.

"I would hope that this is a harbinger of greater use of the power by this president," Love said. "He has not been very eager to use it for ordinary people. A lot of people have applied and a lot of people are waiting and a lot of people are serving excessive sentences."

"They've chosen confrontation rather than compromise or cooperation," Leahy said. "The bottom line on this U.S. attorneys investigation is that we have people manipulating law enforcement. Law enforcement can't be partisan."

At issue is whether the White House exerted undue political influence in the Justice Department's firing of prosecutors.

Leahy's hardening stance is pushing the Democratic-led investigation closer to a constitutional showdown over executive power and Congress' right to oversight.

The White House accused the committee of overreaching.

"After thousands of pages of documents, interviews and testimony by Justice Department officials, it's clear that there's simply no merit for this overreach," presidential spokesman Tony Fratto said.

He said Leahy "is seeking access to candid and confidential deliberations from the president's advisers - an intrusion he would never subject his own staff to. We have gone to great lengths to accommodate the committee in their oversight responsibilities."

Separately, the Senate has subpoenaed the White House and Vice President Dick Cheney's office for documents related to the administration's legal basis for conducting warrant-free eavesdropping on people in the United States.

Leahy and Rep. John Conyers (D-Mich.), who heads the House Judiciary Committee, have demanded a White House explanation by next Monday as to its grounds for claiming executive privilege in refusing to turn over additional documents.

The two lawmakers say that regardless whether the White House meets the deadline, they would begin acting to enforce the subpoenas as appropriate under the law.