WASHINGTON - For the eighth time this year, Senate Republicans blocked a Democratic move Wednesday to challenge U.S. policy in Iraq, turning aside a plan to give troops serving in Iraq and Afghanistan more rest between deployments.

The vote marked another victory for the Bush administration, which lobbied hard against the proposal by Sen. Jim Webb, D-Va., and continued to command the allegiance of congressional Republicans despite persistent public unhappiness with the war.

It also punctuated Democrats' struggles to persuade GOP lawmakers to back legislation designed to limit -- even moderately -- the administration's conduct of the war. Democrats fell four votes short of the 60-vote super-majority demanded by Republican leaders for an amendment to the defense authorization bill.

Six Republicans joined 49 Democrats and one independent in voting for the Webb amendment; 43 Republicans and one independent voted against it.

Frustrated Senate Democrats accused Republicans of abdicating their constitutional responsibility to look out for the wellbeing of the military.

"In blocking this bipartisan bill, Republicans have once again demonstrated that they are more committed to protecting the president than protecting our troops," Senate Majority Leader Harry Reid, D-Nev., said in a statement after the vote.

Republican lawmakers, many of whom were backing a nonbinding alternative, rallied against Webb's proposal as a "back-door" attempt to force a precipitous pullout.

"Every one of us care about the men and women who are serving in the military," said Sen. John McCain, R-Ariz., a leading champion of the current U.S. military strategy in Iraq, who said the measure would "emasculate this surge" just as it was showing signs of success.

"Let us win," McCain said.

In recent weeks, senior Democrats considered dropping their insistence on a withdrawal deadline to force the president to bring home troops, which Republicans have opposed.

Many Democrats had viewed Webb's proposal as the best hope for attracting Republican support.

Webb, a Vietnam War veteran, and his supporters have argued that Congress must alleviate the growing strain on service members, many of whom have served multiple tours overseas since the Iraq war began in 2003.

"The humanity of this is lost," said Sen. Chuck Hagel, R-Neb., another Vietnam War veteran and a leading co-sponsor of Webb's proposal. "It's unfair to continue to load this burden on the same people, deployment after deployment. Not only will you ruin your military ... but you will also have an impact on our society, because a democracy cannot continue to function when you ask 1 percent to make all the sacrifices and carry all the burdens."

The proposal would have prevented the redeployment of active-duty troops to Iraq or Afghanistan until they had been home for the same period of time they were in the war zone. It would have mandated three years between overseas tours for Reserve and National Guard forces.

The measure, a version of which passed the House last month, was backed by the Military Officers Association of America. Earlier this week, several dozen veterans joined Democratic leaders at the Capitol to lobby in favor of the proposal.

In recent days, in an effort to attract support, Webb softened the measure's requirements by giving the Pentagon 120 days to enact it. In a nod to critiques from Defense Secretary Robert M. Gates, he also offered a waiver for special-operations forces.

Get $150+ in coupons in every Sunday N&O. Click here for convenient home delivery.