WASHINGTON — Almost every time President Bush has defended his new strategy in Iraq this year, he has invoked the name of the top commander, General David Petraeus.

Speaking in Cleveland on Tuesday, Mr. Bush called General Petraeus his “main man” — a “smart, capable man who gives me his candid advice.” And on Thursday, as the president sought to stave off a revolt among congressional Republicans, he said he wanted “to wait to see what David has to say. I trust David Petraeus, his judgment.”

With opposition to Mr. Bush’s Iraq strategy escalating on Capitol Hill, the president has sought, at least rhetorically, to transfer some of the burden of an unpopular war to his top general in Baghdad, wielding General Petraeus as a shield against a growing number of congressional doubters. In speeches and meetings, the president has implored his critics to wait until September, when General Petraeus is scheduled to deliver a much-anticipated assessment of the American mission in Iraq.

General Petraeus, a marathon runner with a doctorate from Princeton, is the fourth general to command U.S. military operations in Iraq, but he is the first with whom Mr. Bush has forged such a close relationship. Every Monday, the two men confer via a secure video link without the standard retinue of deputies and aides.

Some of General Petraeus’s military comrades worry that the general is being set up by the Mr. Bush administration as a scapegoat if conditions in Iraq fail to improve. “The danger is that Petraeus will now be painted as failing to live up to expectations and become the fall guy for the administration,” one retired four-star officer said.

Mr. Bush has mentioned General Petraeus at least 150 times this year in his speeches, interviews, and news conferences, often setting him up in opposition to members of Congress.

“It seems to me almost an act of desperation, the administration turning to the one most prominent official who cannot act politically and whose credibility is so far unsullied, someone who is or should be purely driven by the facts of the situation,” said Richard Kohn, a specialist in American military history at the University of North Carolina. “What it tells me, given the hemorrhaging of support in Congress, is that we’re entering some new phase of the end game.”

In his public comments, Mr. Bush has not leaned nearly as heavily on the U.S. ambassador to Iraq, Ryan Crocker, General Petraeus’s political counterpart in Baghdad. At his news conference Thursday, the president mentioned General Petraeus 12 times but Mr. Crocker only twice, both times in his prepared statement. A retired marine lieutenant general, Wallace Gregson, a skilled strategist, concluded that the president is sending the message that Iraq is “a purely military problem.” The lesson, he said, may be that “the military action and the political objectives are parting company.” That is, he explained, the United States may make some progress by fighting insurgents and training Iraqis, but that won’t affect the Iraqi leaders’ ability to achieve reconciliation.

But there was general agreement that the president’s reliance on General Petraeus puts the general in a vulnerable position, both with the administration and with Congress.

When Mr. Bush and his aides shift military strategy, they seem to turn on the generals on whom they once relied publicly, said Lawrence Korb, a former Pentagon official. During the runup to the war, when General Eric Shinseki, the former Army chief of staff, told Congress that more troops were needed to secure Iraq, he was publicly rebuked by then-Deputy Defense Secretary Paul Wolfowitz.

More recently, General George Casey Jr., General Petraeus’s predecessor, was blamed for not doing more to improve security for Iraqi civilians, and General Peter Pace, the chairman of the Joint Chiefs of Staff, was effectively fired last month by Defense Secretary Gates.

“This is an administration that wants to blame the generals,” Mr. Korb said.

It is not unusual for presidents to duck behind generals when wars go bad, Mr. Kohn said. Previous examples, he said, include President Truman relying on General Omar Bradley and the other members of the Joint Chiefs to counter the impact of his split with General Douglas MacArthur over the Korean War, and President Johnson bringing General William Westmoreland back to address Congress in 1967 to respond to the growing antiwar movement.

General Petraeus, however, was not always Mr. Bush’s main man. As commander of the Army’s 101st Airborne Division during the 2003 invasion of Iraq and the first year of the American-led occupation of the country, the general clashed with Mr. Bush’s viceroy, L. Paul Bremer, over several issues, including a decision to bar many former Baathists from government jobs.

Mr. Bush’s current deference to General Petraeus may buy both men a couple of months of relief from intensifying political pressure to set a timeline for withdrawal, but it also propels General Petraeus into the political arena.

General Petraeus, who was confirmed by the Senate with an 81 to 0 vote in February, got a taste of the political battlefield last month when the Senate majority leader, Senator Reid, a Democrat of Nevada, said General Petraeus “isn’t in touch with what’s going on in Baghdad.”

Mr. Reid also questioned the candor General Petraeus had shown in his testimony to Congress. Noting that the general, who is on his third tour of duty in Iraq, oversaw the training of Iraqi troops during his second stint there, the Senate majority leader said, “He told us it was going great; as we’ve looked back, it didn’t go so well.”

General Petraeus has not recoiled from the administration’s effort to use him to promote the decision to send tens of thousands of additional troops to Iraq this year. Shortly before he left for Baghdad in February, he held meetings with members of Congress in the offices of the Senate minority leader, Senator McConnell, a Republican of Kentucky, to tout the plan.

For General Petraeus, the pivotal moment may come in just two months, when he and Crocker return to Washington to testify on the state of the war. A senior officer in Iraq said General Petraeus would point toward several kinds of progress, such as improving security in Baghdad and the shift of tribal alliances in Anbar province away from the insurgency.

But others note that those points were made in the interim report released by the White House on Thursday, without much effect on the political debate. “I am sure in September he will report some progress, but probably not enough to stop the tide to get out now,” predicted Brian Linn, a military historian at Texas A&M University.