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.

“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 after the vote.

Webb’s 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.