WASHINGTON — The White House is rethinking its diplomatic options in Iraq, but won’t reconsider its military strategy before an assessment from war commanders is presented in September, American officials said Tuesday.

President Bush’s top war advisers, Lieutenant General Douglas Lute and Stephen Hadley, went to Capitol Hill to assure Republican supporters that a precipitate pullout of troops won’t happen. Several senators — Trent Lott of Mississippi, Lindsey Graham of South Carolina, John McCain of Arizona, Jon Kyl of Arizona, and others — met with the two advisers in Vice President Cheney’s office off the Senate floor.

Mr. Graham said members were told that Mr. Bush would back them in fiercely opposing legislation by Senator Levin, Democrat of Michigan, that would order troop withdrawals to start in 120 days.

Mr. Bush himself said Tuesday he had no intention of succumbing to political pressure. During a visit to Parma, Ohio on Tuesday, he reiterated that troop levels in Iraq “will be decided by our commanders on the ground, not by political figures in Washington, D.C.”

“I fully understand that this is a difficult war. It’s hard on the American people but I will once again explain the consequences of failure,” he said.

Mr. Graham told reporters the White House is looking at new ways to hasten progress in two primary areas: destroying Al Qaeda in Iraq and forcing the American-backed government in Baghdad to make political progress.

“I think you’re going to find a united front at the White House and to give General (David) Petraeus the time he needs to do nothing to undercut the surge” of troops, Mr. Graham said.

A key progress report being briefed to members Thursday will say the Iraqi government has not met any of its targets for reform but has made some progress in about more than a half-dozen areas, including tamping down violence in Anbar province.

Democrats said the only way Baghdad and its neighbors would take more responsibility in Iraq would be if America starts to pull out.

Mr. Levin and Senator Reed, Democrat of Rhode Island, want legislation that would order Mr. Bush to begin pulling out troops in four months and end combat by April 30, 2008. The measure would allow for some troops to remain to conduct counterterrorism, train the Iraqi security forces and protect American infrastructure.

“There is much too little pressure on Iraqi leaders to do what they have to do,” said Mr. Levin, chairman of the Armed Services Committee.

The presidential spokesman, Tony Snow, earlier Tuesday downplayed the significance of the report coming later in the week, calling it only “a look at the starting line” of the American troop surge.

Mr. Levin’s proposal, offered as an amendment to a $649 billion defense policy bill, is expected to fail because Republicans say they still oppose setting timetables.

But in a sign that GOP frustration with the war is growing, Senator Smith, Republican of Oregon, said he would co-sponsor Mr. Levin’s measure and Senator Snowe, Republican of Maine, said she was considering switching her position and backing the measure. Senator Hagel, Republican of Nebraska, was considered another likely supporter.

Senator Collins, Republican of Maine, Senator Nelson, Democrat of Nebraska, and other moderates said they were considering an alternative proposal that would demand an end to combat and allow American troops to conduct only a narrow set of missions. The measure would not identify a date.

“What many of us are looking for is a new strategy that would not be a precipitous pullout with all of the problems that would cause, but rather a plan to exit over the next year,” said Ms. Collins.

Senator McCain, upon his return from Iraq, defended Mr. Bush’s build up, contending reinforcements had only just recently been put in place.

“I believe that our military in cooperation with our Iraqi security forces are making progress in a number of areas,” he said, noting specifically a dramatic drop in attacks in Ramadi in the western Anbar province.

Mr. Reed of Rhode Island, who also visited Iraq last week, said that Mr. Petraeus, the top commander in Iraq, told him the limits of American military resources will factor into his recommendation on what to do next. “Come next spring, the ability to generate 160,000 soldiers and Marines in country virtually comes to an end,” Mr. Reed said.