WASHINGTON — The first rhetorical shots of a Republican civil war will be fired Monday when the Senate begins debate on a resolution rebuking the president’s plan to send an additional 21,500 troops to Iraq.

While Republican critics of the surge policy persuaded their Democratic colleagues to tone down a version of the resolution passed nearly along party lines in the Senate Foreign Relations Committee last week, those Republican senators who said they would vote for such a resolution are now under fire from the party’s base.

Yesterday, the Senate minority leader tried to make the best of a bad situation. Senator McConnell, a Republican of Kentucky, hosted meetings with representatives of the anti-surge Republican caucus to at least maintain party unity for procedural votes to retain his option to filibuster the compromise resolution sponsored by Senator Warner, a Republican of Virginia, and Senator Levin, a Democrat of Michigan.

“There is an effort to get an alternative resolution to the floor, and there may be a couple of amendments,” a spokesman for Mr. McConnell, Don Stewart, said, acknowledging that the minority leader is not trying to get a unified “nay” vote on the resolutions. “His main focus is to find a way to get all the different viewpoints in the caucus to get a vote. Doing that will allow the members of his caucus to get votes on the resolutions they want.”

Senator McCain, a Republican of Arizona who complained recently that the president is sending too few troops to Iraq, has floated alternative resolutions that set benchmarks for the Iraqi government but support the military surge.

Complicating the matter for Mr. McConnell is a deliberate strategy by the Democratic majority to peel off as many Republicans as possible for an anti-surge resolution. “If we can get significant numbers of Republicans to repudiate the Republican president’s policy, which is about to — about what’s about to happen, then I think that’s very, very positive,” the chairman of the Democratic National Committee, Howard Dean, said on CNN yesterday.

A nationally syndicated conservative talk radio host, Hugh Hewitt, highlighted Dr. Dean’s remarks on his Web log last night as part of his campaign to shame Republican senators into not voting for any anti-surge resolution.

On January 24, Mr. Hewitt launched a drive to collect signatures for a pledge not to vote for or support any Republican who “criticizes the commitment of additional troops to Iraq.” The pledge also states that the undersigned will withhold contributions to the National Republican Senatorial Committee if its chairman, Senator Ensign of Nevada, does not withhold funding for senators who vote for anti-surge resolutions.

The pledge drive has caught the attention of the Senate leadership and the National Republican Senatorial Committee. A spokesman for the committee, Rebecca Fisher, said via e-mail, “The online pledge has had significant support and we have certainly taken notice. While we respect the online community’s right to petition their government, we also hope they realize that the NRSC has a job to do and that is to elect Republicans to the Senate in order to advance the principles of the party for the American people.”

A former speechwriter for President Bush, David Frum, said he sees shades of Vietnam in the antiwar insurgency within his party. “The reason Vietnam destroyed the Democratic Party was because it shattered the party’s internal consensus,” he said. “It may be that a strong defense of the president’s policy will hurt the Republicans in 2008. But the mutiny against the president’s policy, led by Republicans like Senator Hagel, follows the same path that discredited the Democrats for a generation.”