Legislation due to arrive on the U.S. House floor later this month will propose legislation requing the withdrawal of U.S. combat troops from Iraq by the fall of 2008, and even earlier if the Iraqi government does not meet security and other goals, Democratic officials said Wednesday.

The conditions, described as tentative until presented to the Democratic rank and file, would be added to legislation providing nearly 100 billion U.S. dollars the Bush administration has requested for fighting in Iraq and Afghanistan, the officials said.

The legislation would be the most direct challenge the new Democratic-controlled Congress has posed to the president's war policies.

Speaker Nancy Pelosi's office did not provide details, but announced plans for a Thursday morning news conference to unveil the measure. It said she would be joined by Rep. John Murtha, D-Pa., and other key lawmakers. Murtha is chairman of the subcommittee with jurisdiction over the Pentagon's budget and is among the House's most outspoken opponents of the war.

Democrats familiar with the emerging legislation said the bill would require President Bush to certify the government of Iraqi Prime Minister Nouri al-Maliki was making progress toward providing for his country's security, allocating its oil revenues and creating a fair system for amending its constitution.

They said if Bush certified the Iraqis were meeting these so-called benchmarks, U.S. combat troops could remain until September of next year. Otherwise, the deadline would move up to the end of 2007.

The legislation also calls for the Pentagon to adhere to its standards for equipping and training U.S. troops sent overseas and for providing time at home between tours of combat.

At the same time, it permits Bush to issue waivers of these standards. Democrats described the waiver provision as an attempt to embarrass the president, but their effect would be to permit the administration to proceed with plans to deploy five additional combat brigades to the Baghdad area over the next few months.

The measure emerged from days of private talks among Democrats following the repudiation of Murtha's original proposal, which would have required the Pentagon to meet readiness and training standards without the possibility of a waiver.