Sen. Jack Reed, D-R.I., left, accompanied by Sen. Carl Levin, D-Mich., discuss legislation to change the course of the War in Iraq, Tuesday, July 10, 2007, during a news conference on Capitol Hill in Washington. [AP]

In a countermove, President Bush's national security adviser Stephen Hadley and war adviser Lt. Gen. Douglas Lute arrived on Capitol Hill to consult with members.

Sen. Carl Levin, chairman of the Armed Services Committee, proposed legislation with Sen. Jack Reed, D-R.I., that would order President Bush to begin pulling out troops in 120 days 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 U.S. infrastructure.

"There is much too little pressure on Iraqi leaders to do what they have to do," Levin, D-Mich., told reporters.

Democrats are reviving their push for troop withdrawals as a progress report on the war finds Baghdad has not met key targets for security, economic and political reform.

Members said they planned to receive details on the assessment Thursday morning, just as they likely will vote on the Levin proposal.

Rebuffing all such talk, President Bush said he won't succumb 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.

White House spokesman Tony Snow earlier Tuesday confirmed that the coming administration report to Congress would say that Iraq has not met all the benchmarks set for it. The nature of that report was revealed earlier to The Associated Press by a senior administration official, speaking on condition of anonymity.

But Snow argued that the assessment is only "a look at the starting line" of the U.S. troop surge and shouldn't be used by critics to demand withdrawal.

"What Congress will get this week is a snapshot of the beginning of the retooling of the mission in Iraq," he said.

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 a timetable on troop withdrawals.

But in a sign that GOP frustration with the war is growing, Sen. Olympia Snowe of Maine said she was considering switching her position and backing the measure. Also considered likely supporters were Sens. Chuck Hagel of Nebraska and Gordon Smith of Oregon.

Sen. Susan Collins, Ben Nelson, D-Neb., and other moderates said they were considering an alternative proposal that would demand an end to combat and allow U.S. 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 Collins, R-Maine.

Sen. John McCain, upon his return from Iraq, on Tuesday defended Bush's troop build up, contending that 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.

"Make no mistake. Violence in Baghdad remains at unacceptably high levels," McCain added. But the U.S. and Iraq seem to be "moving in the right direction," he said.

Reed of Rhode Island, who also visited Iraq last week, said he did not see enough progress to warrant the U.S. commitment there. Reed said that Gen. David Petraeus, the top commander in Iraq, told him that the limits of U.S. 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," said Reed.

The administration, including Defense Secretary Robert Gates, has stressed a September time frame for a wide-ranging assessment of operational strategy after about 4 1/2 years of battle, and has said such a review would be more appropriate then.

Gates planned to talk to various lawmakers on Tuesday, after abruptly canceling a trip to Latin America this week so he could help shape this week's report to Congress.

Defense Department spokesman Bryan Whitman said that military commanders believe that, "we would be able to be in a better place in September to be able to provide some assessments and make some decisions with respect to the way forward."

So far, he said, commanders are saying the build up ¡ª which brought troops levels to about 157,000 ¡ª has had a "positive" effect.

But concern about continued U.S. troop losses, indications of drift within the government of Prime Minister Nouri al-Maliki in Baghdad and declining public support in this country for the war have driven some key Republicans closer to the position of Democrats demanding withdrawal.

One U.S. official said late Monday that the July report would push the administration to consider its next move. Another senior official, however, said that Bush and his advisers had already decided no change in policy was justified as yet because there was not enough evidence from Iraq.

Whether conditions merited a course shift, such as troop reductions or other scaling back of U.S. operations, would be decided after the September report, said one official, who spoke on condition of anonymity to talk more freely about internal deliberations.

This spring, Congress agreed to continue funding the war through September but demanded that Bush certify on July 15 and again on Sept. 15 that the Iraqis were living up to their political promises or forgo U.S. aid dollars.