House Democrats are writing a fiscal 2007 war spending bill that would require President Bush to bring most U.S. troops home from Iraq before his presidency ends, internal Appropriations Committee documents indicate.

The draft legislation would be the first effort by Congress to impose binding and unconditional demands that U.S. combat operations in Iraq largely end by next year. It comes as the contours of how Democrats hope to debate the issue in both the House and Senate took shape Wednesday.

But it is unclear whether the spending bill could pass the House, because it may be too strong for conservatives but not strong enough for liberals. Senate Democrats face similar problems reaching consensus in their fractured caucus.

The House legislation could be altered before the committee marks up the bill next week.

The memo, prepared by the House Appropriations Defense Subcommittee, said the bill would require the president to certify that Iraq meets key political benchmarks. Failure to do so would trigger a withdrawal of U.S. troops within six months.

Additionally, “If Iraq meets all benchmarks, U.S. troops must be out of Iraq (except to perform certain prescribed functions such as Iraq forces’ training or protecting U.S. diplomatic facilities) by the end of calendar year 2008,” the memo says.

The $100 billion-plus war spending bill would be significant in other respects.

It would require the president to adhere to standards for military readiness and limitations on length of deployments, though he could waive them.

It would prohibit “the initiation of offensive military actions against Iran, except when such operations are authorized by the Senate and House of Representatives, and provides certain waivers,” the memo states.

And the bill would add $4 billion to the president’s emergency defense request, including $1 billion for military operations in Afghanistan, in addition to the billions Congress might add for other programs such as pandemic flu preparations, agriculture disaster relief and children’s health insurance.

Wisconsin Democrat David R. Obey, chairman of the Appropriations Committee, said the supplemental bill was intended “to put pressure on the Iraqis to belly up to the bar and start doing what they are supposed to be doing, which is stop the killing. It is going to be very hard to vote against.”

Pennsylvania Democrat John P. Murtha, who chairs the Defense Appropriations Subcommittee, said the bill puts Congress on the right path. “It gets us where we want to go eventually,” he said. “Whether the surge works or doesn’t work is going to be decided on the ground” in Iraq.

The committee language was still being circulated among a small circle of Democrats on Wednesday, so most House members had not yet reviewed it.

Obey said he was meeting separately with freshmen and with the conservative Blue Dog Coalition Wednesday night, and with the House Democratic whips Thursday. Whether the Democrats decide to move forward with the draft plan, “depends on the outcome of these three meetings,” he said.

Also on Wednesday evening, a group of liberals left a meeting in the office of Speaker Nancy Pelosi, D-Calif., vowing to seek a vote on a measure that would fund a full withdrawal of forces, which they plan to unveil Thursday morning.

Their legislation would direct that federal funding go only for the protection of troops “pending and during” their withdrawal by a specified date, which Barbara Lee, D-Calif., chairwoman of the Out of Iraq Caucus, said would be Christmas 2007.

For now, many liberals are inclined to vote against the supplemental, whether or not they get a vote on their measure, said California Democrat Lynn Woolsey, chairwoman of the Progressive Caucus.

Woolsey acknowledged that the talks involved moving toward requiring troops to come home, but said that they want more clarification before signing on. “We are asking to have those teeth defined,” she said.

The progressives want Democratic leaders to incorporate their language into the supplemental, but that is not likely to happen. Instead, it could be offered as an amendment on the floor of the House.

But the extent to which Democratic leaders will allow amendments to their measure is not yet clear.

Republicans, for their part, have signaled their intention to vote against the supplemental because they believe the readiness standards are too restrictive, and many in the GOP object to any deadline. “I believe members will be able to vote against the supplemental if these issues are not cleared up,” said Minority Leader Roy Blunt, R-Mo.

The White House is preparing to amend its $103 billion supplemental spending request by week’s end, aides said, to redirect at least $2.5 billion. Among other needs, Bush wants to fund 4,000-plus additional support troops to back up the increase of 21,500 U.S. soldiers and Marines in Iraq, which the Pentagon said would cost about $1 billion.

The larger part of the amended request would comprise a combination of money for the Afghanistan military campaign and war-related procurement, notably new mine-resistant vehicles.

But Murtha made it clear that if the administration sends up additional requests, the committee will not consider offsetting cuts. “The bill is set,” he said. “If they send any additional money it will either be added on top, or it won’t be on the bill.”

Meanwhile, Senate Majority Leader Harry Reid, D-Nev., said his caucus would discuss a new Iraq resolution Thursday.

“It’s still such a moving train, the language,” Senate Armed Services Chairman Carl Levin, D-Mich., said Wednesday. “There are people who want to keep it simple and [others who] have a lot of ideas.”

The heart of it, according to the latest draft Levin said he had seen, was binding language that would narrow the scope U.S. actions to missions such as training of Iraqi armed forces, countering terror attacks from al Qaeda and guarding the border.

But like their House counterparts, Senate Democrats continue wrestle over the issue of deadlines. “To get some folks they have to have a date, but if they have a date, they begin to lose me, and others,” said Nebraska Democrat Ben Nelson. “That’s a very delicate thing to be able to achieve, and I’m just not sure it can be achieved.”

Wisconsin Democrat Russ Feingold said he was happy with the most recent Senate version he had seen because it “showed real signs of moving in the direction of getting us out of Iraq, not staying in Iraq.”

Tim Starks, Liriel Higa, Steven T. Dennis, Susan Ferrechio and Jonathan Allen contributed to this story.