Washington ? Under pressure to support the troops but end the war, House Democrats said Thursday they would send President Bush $50 billion for combat operations on the condition that he begin withdrawing troops from Iraq.

The proposal, similar to one Bush vetoed earlier this year, would identify a goal of ending combat entirely by December 2008. It would require that troops spend as much time at home as they do in combat, as well as effectively ban harsh interrogation techniques like waterboarding.

House Speaker Nancy Pelosi had hoped the House would vote as early as today on the bill. But late on Thursday, after meeting with liberal Democrats who were concerned the bill was too soft, she decided to put off debate until next week.

In a private caucus meeting earlier in the day, Pelosi told rank-and-file Democrats that the bill was their best shot at challenging Bush on the war. And if Bush rejected it, she said, she did not intend on sending him another war spending bill for the rest of the year.

“This is not a blank check for the president,” she said at a Capitol Hill news conference following the caucus meeting. “This is providing funding for the troops limited to a particular purpose, for a short time frame.”

White House spokesman Tony Fratto said Bush would veto any bill that sets an “artificial timeline” for troop withdrawals.

“We should be supporting our troops as they are succeeding, not finding ways to undercut their mission,” he said.

Democrats are in a tight spot. Since taking control of Congress in January, catapulted to power by voters frustrated by the war, they remain unable to pass veto-proof legislation demanding troops leave Iraq. Democrats are split on whether to continue paying for the unpopular war, with many saying Congress must provide the military with the money it needs so long as troops are in harm’s way.

Without another spending bill for the war, the Defense Department would have to drain its less urgent accounts to keep the war afloat.

Several anti-war liberals said Thursday they were willing to get behind the measure, so long as Democrats don’t send Bush the money anyway if the bill is vetoed.

“What I don’t want to do is get on this merry-go-round where we try to end this war and negotiate it down to a blank check,” said Rep. Jim McGovern, D-Mass. “It’s time to play hardball.”

The $50 billion included in the bill represents about a quarter of the $196 billion requested by Bush. It would finance about four months of combat, Pelosi said.