A Democratic proposal to withdraw most U.S. troops from Iraq by next year was not expected to overcome Republican opposition in the Senate on Friday.

But despite the anticipated defeat of the measure and earlier failures to change President Bush’s Iraq policy, the Senate’s Democratic leaders dismissed the idea of considering compromise legislation, leaving the chamber at an impasse over the war.

After the defeat on Thursday of an amendment to the defense authorization bill that also would have drawn down most troops from Iraq by next year, the leaders declared they would not give ground on their demands for a fixed withdrawal date merely to pass what they said would be toothless war legislation with the support of some Republican moderates.

“Compromise,” Majority Leader Harry Reid, D-Nev., said, does not mean Democrats will “give up our principles. Our principle is that we need to change the course of the war in Iraq, not have an amendment that we say could pass [with] bipartisan [support].”

Likewise, the Senate’s Republican leaders, who have kept their caucus solidly behind Bush during this week’s Iraq War debate, dug in their heels in support of the president’s war strategy.

Although a number of centrists from both parties sought middle ground, they appeared to be toiling against the wishes of their leaders. The moderates remained hopeful that Democratic leaders, in particular, would agree to consider several compromise measures on the war next week, by which time the toughest proposals would likely be dead.

But as lawmakers prepared for the Friday vote, there were no signs that party leaders would bend.

The vehicle for the Senate’s Iraq War debate was the $648.3 billion defense authorization bill (HR 1585). Thursday’s most substantive vote was a 28-70 defeat of an amendment by Russ Feingold, D-Wis. It would have required U.S. troops to begin withdrawing from Iraq in 90 days and to complete their pullback by the end of June 2008, with exceptions for limited missions, including troops needed to fight terrorists and train Iraqi forces. After that date, no funding would be allowed for the war.

On Friday, the chamber is scheduled to take up an amendment by Democrats Carl Levin of Michigan, who chairs the Armed Services Committee, and Jack Reed of Rhode Island, a committee member and West Point graduate.

That amendment would require a withdrawal of U.S. forces from Iraq to begin in 90 days and end in nine months, leaving behind a force similar to the one Feingold envisioned.

The Levin-Reed amendment does not carry a funding cutoff, but it was expected to fail to win the 60 votes needed.

The Senate also may vote on a “sense of the Senate” resolution that would say the policy of the United States is to “combat, contain and roll back” Iran and its surrogates in Iraq.

The resolution, by ­Republican Jon Kyl of Arizona and Joseph I. Lieberman of Connecticut, an independent who caucuses with the Democrats, also would express the Senate’s view that Iran’s Revolutionary Guard should be designated a terrorist organization, a move the Bush administration is now considering.

Thursday’s vote on the Feingold measure was the first direct attempt by Democrats to force a withdrawal since July 18, when Reid pulled the defense authorization bill from the floor after failing, 52-47, to limit debate on an earlier Levin-Reed proposal that would have withdrawn U.S. troops from Iraq by April 30, 2008.

Some lawmakers on both sides of the aisle had hoped that Democrats, after appeasing their most ardent anti-war supporters by holding votes on withdrawal measures, might seek more measured approaches in the interest of passing legislation. But that appears unlikely, at least for now.

Levin had hoped to get a vote soon on a version of his amendment that would make the withdrawal date a non-binding goal rather than a requirement. But although Democrats did not rule out that possibility, they also did not sound interested in it Thursday.

“To do something that doesn’t do anything doesn’t do much good,” said Charles E. Schumer of New York, vice chairman of the Democratic Caucus.

“We are not changing our strategy. We feel extremely comfortable with where we are,” Reid said. “Now it’s Bush’s war and the Republican senators’ [war].”

Earlier this month, Reid was more amenable to compromise, saying that “nothing is off the table.” But he told reporters Thursday he had grown frustrated that Republicans would not accept his overtures.

Republican moderates, particularly those facing tough re-election campaigns in states where the Iraq War is unpopular, want Reid to continue to press for a middle ground.

“When we first came back [from the August recess], I thought he really wanted to compromise. Now it seems like that’s changed,” said Republican Susan Collins of Maine. “The question for Democrats is do they really want to force a change in policy in Iraq?”

Gordon H. Smith of Oregon, one of a handful of Republicans who voted for the Levin-Reed amendment in July — and who is among those up for re-election next year — said the mantra of Reid and other Democratic leaders is now, “Tee up the ’08 elections and subordinate honorable compromise and good government.”

Moderate Republicans such as Collins, Smith, John W. Warner of Virginia, George V. Voinovich of Ohio, Lamar Alexander of Tennessee and Norm Coleman of ­Minnesota have been meeting almost daily with Democratic centrists, including Ben Nelson of Nebraska and Ken Salazar of Colorado, to come up with a legislative formula both sides can embrace.

But by all accounts, their negotiations have gone nowhere because proposals that attract members of one party tend to repel members of the other, making a middle ground hard to find.

“That’s been the problem from the very beginning,” said Nelson.

The Bush administration, aware of the decisive role that GOP moderates could play in any war legislation, has continued to lobby them hard. Defense Secretary Robert M. Gates was back on Capitol Hill early Thursday to attend a meeting of two dozen House Republicans, including many centrists, and keep them in line.

Bart Jansen and Alan K. Ota contributed to this story.