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By Richard Cowan

WASHINGTON, Nov 14 (Reuters) - The Democratic-led U.S. House of Representatives on Wednesday approved a timetable for withdrawing troops from Iraq, defying President George W. Bush by tying the measure to $50 billion in new war funds.

By a vote of 218-203, the House sent the controversial plan to the Senate, where it faced an uphill fight as Republicans have vowed to block it.

White House spokeswoman Dana Perino called on Congress to send Bush a "clean" emergency funding bill, without withdrawal dates.

"If legislation comes to the president in this form, he will certainly veto it," Perino said in a statement after the House vote.

The House vote came on the same day that an explosion in Baghdad brought more U.S. casualties, adding to what already was the Iraq war's bloodiest year for American forces.

The House bill, backed by four Republicans, is similar to a plan Bush vetoed in May that would have begun the immediate withdrawal of some U.S. combat troops from Iraq, who have been fighting there since March 2003.

By Dec. 15, 2008, all American combat soldiers would be out. In a disappointment to liberal Democrats, that date would be a nonbinding goal.

"It will set parameters and it will say, 'Mr. President, we need to change policies,'" said House Majority Leader Steny Hoyer, a Maryland Democrat.

Anti-war Democrats increasingly are challenging their leaders to withhold any more money for the war unless new conditions are placed on Bush, who has talked about a long-term military commitment in Iraq.

In warning of a presidential veto, the administration said it opposes setting any "arbitrary date" for withdrawal. The Democrats' bill "unwisely abandons the cause of freedom and stability in the Middle East," it said.

The $50 billion in new funds, far below the $196 billion Bush has requested for the wars in Iraq and Afghanistan, would last an estimated four months. Democrats hope the money would be used to start changing the U.S. mission from one of combat to protecting U.S. facilities there, training Iraqis and conducting counter-terrorism operations.

The measure also would prohibit U.S. officials from using torture in interrogations. Bush says that already is prohibited. But he refuses to disclose interrogation methods and there have been reports of the CIA using "waterboarding," or simulated drowning on some detainees.

House Speaker Nancy Pelosi, a California Democrat and vocal war opponent, told her colleagues this would be the final vote on war funding this year -- even if Bush were to veto the bill, according to sources.

Republicans have mocked the succession of unsuccessful votes that Democrats have held this year in the House and Senate to put an end-date on the Iraq war. Many bills were advanced since January, when Democrats claimed a slim majority in Congress, knowing they lacked enough votes to overcome opposition from Bush and congressional Republicans.

Senate Majority Leader Harry Reid has indicated he will try to corral enough votes for passage this week in the more troublesome Senate. (Additional reporting by Thomas Ferraro, editing by Doina Chiacu)

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