WASHINGTON, June 20 — When Senator John Kerry was their presidential nominee in 2004, Democrats fervently wished he would express himself firmly about the Iraq war.

Mr. Kerry has found his resolve. But it has not made his fellow Democrats any happier. They fear the latest evolution of Mr. Kerry's views on Iraq may now complicate their hopes of taking back a majority in Congress in 2006.

As the Senate prepared for what promises to be a sharp debate starting on Wednesday about whether to begin pulling troops from Iraq, the Democratic leadership wants its members to rally behind a proposal that calls for some troops to move out by the end of this year but does not set a fixed date for complete withdrawal. Mr. Kerry has insisted on setting a date, for American combat troops to pull out in 12 months, saying anything less is too cautious.

In drawing up a schedule for the Wednesday session, the Democratic leadership has arranged for its plan to be debated first, pushing Mr. Kerry and his proposal into the evening, too late for the nightly television news, to starve it of some attention.

Senate Democrats have been loath to express their opinions publicly, determined to emphasize a united front. But interviews suggest a frustration with Mr. Kerry, never popular among the caucus, and still unpopular among many Democrats for failing to defeat a president they considered vulnerable. Privately, some of his Democratic peers complain that he is too focused on the next presidential campaign.

Mr. Kerry now describes the war in Iraq as a mistake, even though he once supported it. His critics say they believe the new stand reflects more politics than principle, and ignores other Democrats' concern that setting a fixed date will leave those in tough re-election fights open to Republican taunts that they are "cutting and running" in Iraq.

The Democrats' exasperation has increased in the last week, as they postponed a vote on Mr. Kerry's amendment to try to fashion a broader consensus among themselves. Democrats up for re-election asked him not to propose a fixed date. But Mr. Kerry, several Democrats said, was unwilling to budge from that idea, even though his co-sponsor, Senator Russell D. Feingold of Wisconsin, seemed willing to compromise for the sake of consensus. In the end, Mr. Kerry agreed only to extend his deadline, from Dec. 31 of this year to July 2007.

Mr. Kerry's insistence on pushing ahead with his own plan has left the Democrats divided, and open to renewed Republican accusations that they are indecisive and weak — the same ridicule that Republicans heaped on Mr. Kerry in 2004, when his "I was for it before I was against it" statement about a vote on money for the war became a punch line.

"There are certain Democrats who think that this is over, that we've lost or that there's nothing constructive the president is going to do," said Senator Joseph R. Biden Jr. of Delaware, who, like Mr. Kerry, is considering running for president and who sat in on the meetings where Democrats searched for consensus. "What it really is, in fairness to them, is a frustration that they see no learning curve on the part of this administration. I can understand that frustration. But setting a date is not a plan."

Stepping into an elevator on Capitol Hill late last week, Mr. Kerry was asked whether he was under pressure in the Democrats' meetings to withdraw his proposal. As he insisted he was not, Senator Christopher J. Dodd, Democrat of Connecticut, standing behind him, raised his eyebrows, then winked.

In an interview, Mr. Dodd, who is also considering a presidential run, said one danger in the November election was in making Democrats look indecisive. "If the argument comes down to, Is it one year or 18 months, I think we're going to confuse people," he said. "I'm not sure what the value is; I think it hurts us rather than helps."

Polls suggest many Americans are eager to see American troops come home from Iraq but are uneasy about leaving too soon. The rival Democratic approaches may reflect that tension, with Mr. Kerry appealing to those who regard the war as a mistake, while the Democratic leaders reflect more caution.

Matt Bennett, a spokesman for Third Way, a group of moderate Democrats, said his organization preferred an approach that did not set a date, proposed by Senators Carl Levin of Michigan and Jack Reed of Rhode Island. Of Mr. Kerry's stance, Mr. Bennett said: "He feels like he needs to sharpen his position. But voters can sense when you're being resolute for convenience sake, or for political advantage."

Some Democrats felt Mr. Kerry allowed Republicans to embarrass them in a vote last week, when the Republicans embraced Mr. Kerry's proposal, certain it would be defeated and allow them to declare themselves the party of unity and strength.

In a telephone interview on Tuesday, Mr. Kerry characterized his statement as the position of strength, and said Democrats had made a mistake not to take a firm stand.

"The Democrats need to be strong and stand up with a clear articulation about how we make the United States stronger," he said. "As far as I'm concerned, we should go right at Karl Rove and his phony tough talk that is calculated purely for the election and not for a successful strategy in Iraq."

"I'm doing what I think is the right thing to do as a policy matter," he said, "for our troops and for the country. Someone else will deal with politics."

Mr. Kerry said he did not want to analyze his campaign mistakes but insisted he had been firm. "What's clear is that I said that it was the wrong war, wrong place, wrong time," he said. "I couldn't have been clearer about the president mishandling the war."

The Democrats tried to minimize their differences. Mr. Levin said differences among Democrats were not as big as the differences between Democrats and Republicans.

"One thing the Democrats agree on is that this war has taken too long, is too expensive and has cost too many lives," said Senator Harry Reid of Nevada, the minority leader.

Senator Charles E. Schumer of New York, chairman of the Democrats' effort to take control of the Senate, minimized the effect the vote would have in November.

"The public and the voters are looking at how George Bush handles Iraq," he said. "They know that he got us in there, they know he's the commander in chief, and they don't believe he has figured out a strategy that will show light at the end of the tunnel. That is the overriding issue in the election, far more than what Democrats are doing."

Mr. Feingold, Mr. Kerry's co-sponsor, said: "There should be no political considerations, there should be only considerations for the security of the American people. I believe the American people, even in conservative states, are willing to see this end."

He said that a year ago he was the only senator calling for a withdrawal. "This is building," he said. "The American people are actually way ahead of the Senate on this."

Although Mr. Kerry's approach is to be debated last, the Democratic leadership has arranged that it be voted on first, before the Levin-Reed proposal. In the interview, Mr. Kerry said that if his amendment failed, he might consider voting for the alternative "as a means of making some statement." But, he said, "My preference is, we take some strong position that's got a date."