Efforts to bring a faster end to U.S. involvement in the Iraq War were dealt a potential setback Thursday when a majority of the Senate, including two key moderate Democrats, voted against Senate Majority Leader Harry Reid’s (D-Nev.) proposal to require a redeployment of troops from Iraq by March 2008.

Democratic Sens. Ben Nelson of Nebraska and Mark Pryor of Arkansas joined 47 Republicans and Independent Democratic Sen. Joe Lieberman (Conn.) in opposing the Reid resolution. Although Sen. Gordon Smith (R-Ore.) did join with the bulk of Democrats in voting for the measure, Reid narrowly avoided loosing a third Member from his own party during the vote.

Sen. Ken Salazar (D-Colo.) — originally a co-sponsor of the resolution who later withdrew his name — appeared set to vote against the measure. But Reid and Democratic Senatorial Campaign Committee Chairman Sen. Charles Schumer (N.Y.) flanked Salazar, urging him to vote with the party. Salazar, who cast the last vote on the measure, eventually sided with Reid.

The Senate also approved by wide margins two largely symbolic resolutions supporting troops in the field, one by Sen. Judd Gregg (R-N.H.) and the other by Sen. Patty Murray (D-Wash.). Democratic aides prior to the vote had said they hoped the Murray resolution — which closely resembled the Gregg measure — would siphon off enough votes to keep Gregg from reaching the 60-vote mark needed for passage.

Republicans hailed the votes as proof that a majority of the Senate is not ready to formally break with President Bush’s plans for Iraq, and warned that it was a signal that likely future efforts to end the war would continue to fail. Senate Republican Conference Chairman Jon Kyl (Ariz.) argued the vote should give Reid pause if he plans to attach the language to the upcoming military supplemental spending bill, saying the vote shows “an overwhelming number of Senators want to see appropriate funding” levels in the bill and that “it is now clear that a majority do not support the Reid language.”

In fact, while Reid has previously said he would definitely look to attach the resolution to the supplemental, following today’s vote he seemed less certain, saying he would meet with Speaker Nancy Pelosi (D-Calif.) and Senate chairmen to discuss how to proceed.

Should Reid decide to make a pass at attaching the Iraq language to the supplemental, he could face renewed challenges from the right and left. Nelson and Sen. John Warner (R-Va.) are working with other moderate members on an alternative that would give Bush until September to show his new plans for the Iraq War are working. And aides said today that liberal members led by Sen. Russ Feingold (D-Wis.) could look to include provisions forcing a much more rapid redeployment of troops than is envisioned in the Reid language.