Washington ? As the House opened debate Thursday on a proposal that would force the withdrawal of U.S. combat troops from Iraq by September 2008, Democratic leaders scrambled to round up the votes they need in their biggest showdown to date with the White House over the war.

The fate of the legislation, which is expected to come to a vote today, is unclear. Several Democrats chafe at the idea of supporting a measure – a $124 billion spending bill for the Iraq and Afghanistan wars – that gives more money to an increasingly unpopular cause and many Republicans deride the plan as a mandate for failure.

But the Democratic leadership appeared to gain momentum late Thursday when Rep. Maxine Waters, D-Calif., announced that the Out of Iraq Caucus, a group of legislators who support cutting off funding of the war and want the troops home sooner, has released members to vote in favor of the legislation.

Waters would not say how many from the caucus would vote for it, but she said several members would vote with the House Democratic leadership in favor of the measure.

“We told them, ‘If you really feel uncomfortable voting no, you are released to vote yes,'” said Waters, who said she plans to vote against the measure. “We don’t want you to be in a position that you feel you’re undermining your political career.”

Still, the Democrats’ struggles with the bill highlight the divisions within the party on how to rein in the war, despite the widespread belief that anti-war sentiment propelled the Democrats to their takeover of Congress in the November election. Conservatives are concerned about withdrawing troops, and liberals do not want to vote for continued spending.

The September 2008 deadline is part of the spending bill, and the new Democratic majority has added billions in nonmilitary home state appropriations to persuade moderate Republicans and Democratic fence-sitters to vote in favor of it. Meanwhile, the Senate Appropriations Committee passed a similar measure that calls for troops to be pulled out by March 31, 2008.

The White House warned Democrats again Thursday that President Bush would veto the legislation and said Democrats were putting troops in peril by not quickly passing a spending bill to pay for the war. Defense Secretary Robert Gates added that any delay in passing the spending bill would have an “adverse” effect on the troops.

President Bush said, “Congress needs to get their business done quickly, get the monies we’ve requested funded, and let our folks on the ground do the job.”