WASHINGTON — Speaker 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 Mr. Bush. It would finance about four months of combat in Iraq, Ms. Pelosi told reporters today.

“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 sets a goal that combat end by December 2008. After that, troops left behind should be restricted to a narrow set of missions, namely counterterrorism, training Iraqi security forces and protecting American assets.

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

Ms. Pelosi said the bill also would require that the government rely on an Army field manual when conducting interrogations.

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.

Ms. 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. They oppose setting a timetable for troop withdrawals.

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.

Today, the House and Senate were on track to approve $460 billion in annual military spending, as well as a stopgap funding measure to keep the rest of the government running through mid-December.

Without the $50 billion for combat operations, the Defense Department would have to transfer money from less urgent spending accounts to keep the wars afloat.

The top Republican on the Senate Defense Appropriations Subcommittee, Senator Stevens of Alaska, predicts the Army would run out of money entirely by January if Congress does not approve some war money.