WASHINGTON — Speaker Nancy Pelosi said the House will vote as early as Friday on legislation that would spend $50 billion on the wars in Iraq and Afghanistan but require that President Bush start bringing troops home.

The money is about a quarter of the $196 billion requested by Bush. It would finance about four months of combat in Iraq, Pelosi told reporters on Thursday.

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

The bill would set the requirement that troop withdrawals begin immediately and that soldiers and Marines spend as much time at home as they do in combat.

The measure also identifies a goal that combat end by December 2008. After that, troops left behind should be restricted to a narrow sets of missions, namely counterterrorism, training Iraqi security forces and protecting U.S. assets, Democrats say.

Bush rejected a similar measure in May, and Democrats lacked the votes to override the veto.

The latest proposal was headed on a similar path, with Republicans immediately sounding their objections.

"It's a proposal so backward and irresponsible that it can only be explained as political stunt," said House Republican Leader John Boehner, R-Ohio.

Pelosi said the bill also would require that the government rely on an Army field manual when conducting interrogations.The field manual was updated in 2006 to specifically ban aggressive interrogation techniques including waterboarding, or simulated drowning, believed to have been used by the CIA.

Since taking control of Congress in January, Democrats have struggled to challenge the president on the war. Holding a shaky majority, they lack the votes to overcome procedural hurdles in the Senate or override a presidential veto.

They also remain divided amongst themselves on how far to go to end the war; many Democrats oppose setting a firm timetable on troop withdrawals, and prefer instead setting a nonbinding goal.

Pelosi's measure will likely scrape by the House but become hamstrung in the Senate over Republican objections. Buoyed by recent progress in Iraq, where enemy attacks have declined but political efforts remain in a stalemate, GOP lawmakers are more hopeful than ever that the war is turning a corner.

"Our troops need all of the resources Congress can provide to seize upon the tactical momentum they've achieved and eliminate al-Qaida from Iraq's communities once and for all," said Boehner.

Republicans also would likely oppose applying Defense Department interrogation standards government-wide because it would limit the CIA's use of aggressive techniques against high-value terrorism suspects.

Some anti-war Democrats were expected to oppose the measure as well, on the grounds that it funded an unpopular war and wouldn't require that Bush end the war. In a private caucus meeting early Thursday, Pelosi sought to shore up support among rank-and-file members by describing the bill as the best shot Democrats had to challenge Bush.

The proposal sets "goals instead of guarantees and that makes it a little soft for me," said Rep. Lynn Woolsey, D-Calif., a leading anti-war liberal.

On Thursday, the House approved $460 billion in annual military spending and $11.6 billion for bomb-resistant vehicles for the war, as well as a stopgap funding measure to keep the rest of the government running through mid-December.

The spending package omits money for the war.

Without money for combat operations, the Defense Department would have to transfer money from less urgent spending accounts to keep the wars afloat.

Sen. Ted Stevens of Alaska, the top Republican on the Senate Appropriations defense subcommittee, said he believes the Army would run out of money entirely by January if Congress does not approve some war money.

Senate Majority Leader Harry Reid said he did not want to approve a spending measure for Iraq unless it forced a change in Bush's policies. When asked whether that was possible, considering the razor-thin majority Democrats hold in the Senate, Reid said it "is up to the White House and up to the Republicans."