Rep. John Murtha predicted Monday that Democrats will not be able to pass any meaningful legislation to end the Iraq war until presidential primary elections are over next year.

Murtha, a Vietnam veteran and war critic who chairs the appropriations subcommittee overseeing defense spending, conceded that not as many Republicans had broken with President Bush as many Democrats had predicted.

"As soon as the primaries are over, you're going to see Republicans jumping ship," Murtha, D-Pa., said in a speech at the National Press Club.

He said it will be difficult to get the 60 votes needed in the Senate to pass a withdrawal measure through Congress. Primaries are scheduled into next June.

"I see what happens to a Republican when they say we ought to start to get out," Murtha said. "They bash them. I mean they attack them viscerally and of course they're the ones that nominate them. Until that plays out we're going to have a problem."

After the speech, Murtha said he's been told privately by some Republicans who publicly support the war that they are opposed to it.

Senate Democrats have expressed confidence that they can pass legislation to give troops more rest between Iraq deployments, a measure aimed at pressing the Bush administration to change its war policy.

Defense Secretary Robert Gates called the proposal by Sen. Jim Webb, D-Va., a dangerous "backdoor way" to draw down additional forces. Gates said he would recommend a veto.

"If we get this next phase wrong — no matter how you feel about how we got to where we are, the consequences of getting this wrong for Iraq, for the region, for us are enormous," he said Sunday.

President Bush last week announced plans for a limited drawdown but indicated combat forces would stay in Iraq well past 2008.

The Senate was scheduled to resume debate this week on anti-war legislation, including Webb's proposal to require that troops have as much time at their home station as they do deployed to Iraq.

Supporters of Webb's measure say it has at least 57 of the 60 votes needed. It would need 67 votes to override a veto.

A separate proposal by Sen. Carl Levin, D-Mich., seeks to restrict troops' mission to fighting terrorists and training the Iraqi security force.

If Webb's amendment were enacted, Gates said it would force him to consider again extending tours in Iraq. Military commanders would be constrained in the use of available forces, creating gaps and forcing greater use of the National Guard and Reserve, he said.

"It would be extremely difficult for us to manage that. It really is a backdoor way to try and force the president to accelerate the drawdown," Gates said. "Again, the drawdowns have to be based on the conditions on the ground."

Active-duty Army units currently are on 15-month deployments with a promise of no more than 12 months rest. Marines who spend seven or more months at war sometimes get six months or less at home.

Bush said last week that he approved a plan by Gen. David Petraeus, the top U.S. commander in Iraq, to withdraw 5,700 troops from Iraq by the holidays and reduce the force from 20 combat brigades to 15 brigades by next July.

The president has ordered Petraeus to make a further assessment and recommendations in March.

There are about 169,000 U.S. troops in Iraq.

Gates on Friday raised the possibility of cutting troop levels to 100,000 or so by the end of next year, well beyond the cuts Bush announced, in what appeared to be a conciliatory gesture to anti-war Democrats and some wary Republicans.

But on Sunday, Gates said he could not say how large the force would be in the coming years, stressing that it would depend on whether the security situation in Iraq had improved dramatically.

Gates spoke on "Fox News Sunday" and "This Week" on ABC. Reed was on ABC and Levin appeared on "Face the Nation" on CBS.