WASHINGTON – A bipartisan consensus to dramatically alter the U.S. military mission in Iraq began to emerge Wednesday in the Senate, but no specific approach has yet attracted the broad support necessary for a veto-proof majority.

Senate Majority Leader Harry Reid has so far refused to bend on his demand for a firm timeline for troop withdrawals, despite signs that a growing number of Republicans may agree to slightly weaker measures that would still force President Bush to immediately change his Iraq strategy. Potential GOP defectors now number about 10.

Surprising even his colleagues, Reid harshly dismissed the measure with the broadest bipartisan backing – a compilation of Iraq Study Group recommendations offered by freshman Democrat Ken Salazar of Colorado. The Salazar proposal, which as of Wednesday night had attracted six Democratic and six Republican co-sponsors, “won’t change one thing that the president does,” Reid said.

His opposition to anything short of legislation ending U.S. combat operations shows that the chasm between the parties remains fairly wide.

The Senate is focused on four proposals: One is Salazar’s, which would adopt the study group’s plan but gives the president latitude to make withdrawal timetables; another advanced by Sens. Ben Nelson, D-Neb., and Susan Collins, R-Maine, would force an immediate end to the U.S. combat mission without mandating troop withdrawals; another, still in the works by Sens. Richard Lugar, R-Ind., and John Warner, R-Va., that would meld the two; and the main Democratic plan, sponsored by Armed Services Chairman Carl Levin, Mich., and Sen. Jack Reed, R.I., would begin troop reductions no later than 120 days after enactment.

Support for that provision remains far short of the 60 needed for passage much less the two-thirds Senate majority needed to override a presidential veto. But it received a significant boost Wednesday when two Republican senators, Olympia Snowe, Maine, and Chuck Hagel, Neb., signed on. Snowe has long been a critic of the war but had until Wednesday refused to support any mandated troop reductions.

Snowe’s endorsement is a shift for the senator, who in recent months opposed a similar measure. Snowe had said earlier that she’d been considering signing on to the measure because the situation in Iraq was growing worse.

“We have arrived at the crossroads of hope and reality, and we must now address the reality. We need to send a strong message from the United States Congress on behalf of the American people that the current strategy is unacceptable,” she said.

Votes on all the mission-related amendments are expected next week. Meanwhile, the House will debate and vote Thursday on a free-standing bill mandating that troop withdrawals begin in 120 days, with most of them out by April 1, 2008.

Reid’s steadfastness prompted questions by many senators as to whether the Senate leadership actually wanted legislation that could garner the necessary 60 votes – or whether Reid would prefer to keep Republicans on the defensive, for political reasons.

“We’re playing yo-yo, political yo-yo with people’s lives, and the country cannot survive this way of allowing the constitutional balance that has given us freedom for 200-something years to be changed because of the poll of the moment and the next election,” said Sen. Lindsey Graham, R-S.C., a strong Bush ally.

But for now, Democratic unity appears to be forcing Republicans to take firmer stands against the president’s policies.

Wednesday, on the first in a series of Iraq amendments to the annual defense policy bill, seven GOP senators voted with Democrats to break a Republican filibuster of a proposal from Sen. Jim Webb, D-Va., to require longer troop rest periods between combat deployments. Six of the seven Republicans are vulnerable 2008 incumbents. The effort still failed 56-41, with 60 votes needed for passage. But the seven Republican votes were surprising, considering that a similar measure in the House last spring was roundly denounced by Republicans as a “slow bleed strategy.”

Nelson and Collins officially introduced their amendment Wednesday, seeking to drum up support for a measure they say would force a sharp change in the mission in Iraq and a drawdown of forces without timelines.

Under the provision, the president would have to immediately shift U.S. forces from combat roles to protecting U.S. personnel in Iraq, training Iraqi security forces, securing the Iraqi border and fighting terrorism. The amendment sets a goal of completing that mission change by March 31, 2008.

The Democratic plan sponsored by Levin and Reed would begin troop reductions no later than 120 days after enactment. U.S. forces would then shift their efforts to targeted missions such as counterterrorism. The process would have to be completed by April 30, 2008.

Sen. Gordon Smith of Oregon signed on to the Levin-Reed plan earlier this week. Hagel added his support when Democrats agreed to include his proposal that an international mediator be brought in to try to end the war under the auspices of the United Nations.

The Associated Press contributed to this report.