Legislation to regulate U.S. troop deployment cycles in Iraq was blocked in the U.S. Senate late Wednesday by Republican opponents who argued the measure could undermine the war effort. The action was a blow to Senate Democrats who are seeking to challenge the Bush administration's Iraq war policy. VOA's Deborah Tate reports from Capitol Hill.

The Senate voted 56 to 44, four short of the 60 necessary, to cut off debate and move the measure to a final vote.

The legislation would have ensured that troops returning from Iraq and Afghanistan be allowed to spend at least as much time at their home bases as they spent on their last deployment before returning to the battlefield. Most troops spend about 15 months in combat and 12 months at home.

Senator Jim Webb, a Virginia Democrat and Vietnam veteran who also served as navy secretary under the Republican administration of President Ronald Reagan, was the chief sponsor of the measure. "It is needed for the well being of our troops and family members," he said.

Opponents said the measure would allow Congress to micromanage the war.

Senator John McCain of Arizona, himself a Vietnam veteran who is seeking the Republican nomination for president next year, argued that political - not military - considerations were behind the proposal. With the military stretched thin by the mission in Iraq, McCain said extending troops' time away from the battlefield would amount to a de facto troop withdrawal from Iraq. "This debate is about whether we will force a backdoor approach aimed at influencing the conduct of the war," he said.

Senator John Warner, a Republican of Virginia, who, like Senator Webb, is also a former navy secretary, had initially supported the proposal but changed his mind after talking with senior military officials. "They are absolutely convinced, and have now convinced me that they cannot effectively put into force that amendment at this time without causing severe problems within the existing forces and those that are serving there," he said.

Warner had voted for the legislation when it first came before the Senate in July, when it also fell short of the 60-vote margin.

Senator Webb said he believes Warner's reversal on the measure prompted other Republicans who may have considered supporting the proposal to back away from the plan.

Defense Secretary Robert Gates said he would have recommended that President Bush veto the legislation had it passed, even though Senator Webb said the president could waive the provisions if he deemed it necessary for national security.

Senate Majority Leader Harry Reid, a Nevada Democrat, who has been frustrated by Republican efforts to block legislation aimed at changing the course of the Iraq war, again expressed his disappointment. "To stop the majority of this body from acting shows yet again that most of my Republican colleagues are much more interested in protecting the president than protecting our troops," he said.

Senate Democratic leaders had viewed the Webb proposal as having the best chance of attracting the 60 votes necessary to allow for passage of the measure.

Its defeat calls into question whether Democrats, under pressure from members of their liberal base to end the war quickly, will be able to get any measures aimed at challenging Iraq war policy approved in the coming weeks and months.

Senator Chuck Hagel, a Nebraska Republican and co-sponsor of the legislation, does not see members of his party breaking with the president any time soon.

"Most of the Republicans will stay with the president in his status quo part two or stay the course part two, until probably until after the first of the year. I do not think there will be any meaningful change of votes or switching positions until we get into next year. I just don't think that will happen," he said.

But Senator McCain said many Republicans want to give President Bush's troop surge more time to work following testimony last week by the top commander in Iraq, General David Petraeus, that the surge is working and has resulted in some progress in Iraq.

Debate on troop deployment cycles came as the Senate considered a defense policy bill.