WASHINGTON — Senate Republicans on Thursday blocked President Obama’s nominee to lead the Pentagon, in a defiant move likely to further strain partisan tensions while preventing the White House, at least temporarily, from assembling its second-term national security team.
In a result that broke down almost strictly along party lines, Democratic senators could not muster the support to advance the nomination of Chuck Hagel, a former Republican senator from Nebraska, to a final vote. The vote was 58-40, falling short of the 60 that were needed.
Democrats vowed to try again to save the nomination of Hagel, a decorated Vietnam veteran, when the Senate returns from recess in 10 days. Several Republicans who voted against Hagel said they would not block a final vote.
Democrats accused the opponents of mounting the first-ever filibuster against a Pentagon chief for their own political purposes.
‘‘Just when you thought things couldn’t get worse, it gets worse,’’ said Senator Harry Reid, the Nevada Democrat and majority leader. ‘‘I guess to be able to run for the Senate as a Republican in most places of the country, you need to have a resume that says, ‘I helped filibuster one of the president’s nominees.’ ”
The vote represented the first time in history that the Senate has required that a nominee for secretary of defense clear the 60-vote hurdle before a final, simple majority vote.
Republicans, who took the extraordinary step of rebuffing their former colleague and fellow party member, insisted that Democrats were trying to rush a vote on a crucial Cabinet position that deserved more consideration.
‘‘We didn’t need to have this vote today,’’ said Senator John Cornyn of Texas, the second-ranking Senate Republican. ‘‘But the White House and the majority leader were determined to have this vote in order to try to get a story in the newspaper, one that misrepresents the nature of the objection on this side.’’
All day, a tense standoff played out in the Capitol as one party tried to force the other into a more politically undesirable position. Republicans, calculating that Democrats might want to avoid forcing a vote that could result in an embarrassing setback for the president, had hoped to press Reid to back down and reschedule after the Senate returns from its recess.
Democrats, mindful that Republicans did not want to be blamed for jeopardizing the Pentagon’s stability for political purposes, decided to press ahead and require Republicans to record a vote against Hagel.
While the showdown vote was set for Friday morning, just after 3 p.m. on Thursday Reid came to the Senate floor to move that instead it be called at 4:15. That forced such Republican senators as John McCain of Arizona and Lindsey Graham of South Carolina, both members of the Senate Armed Services Committee who have said that they find the act of filibustering a defense secretary distasteful, to cast votes that had the same result as a filibuster, even if they refused to call it that.
Four Republicans joined Democrats in voting that debate on the nomination should end: Senators Thad Cochran of Mississippi, Susan Collins of Maine, Mike Johanns of Nebraska, and Lisa Murkowski of Alaska. Senator Orrin G. Hatch of Utah voted present because he said he was wary of the precedent a no vote would set, even though anything other than a yes vote had the same practical effect on the outcome.
Because of parliamentary rules, Reid voted with Republicans to allow him to bring the Hagel nomination back for another vote. Counting Reid, Hagel was actually one vote shy of the 60 needed.
Given the outcome, a major matter of concern for the White House over the next 10 days is that Hagel’s opponents — an array of groups that includes conservative and pro-Israel forces — could intensify their campaigns to defeat his nomination.
Leaders of these groups said they expected their efforts to include more phone calls urging conservative voters to tell their senators to vote no; new efforts to unearth embarrassing details from Hagel’s past; and, potentially, a new round of television advertisements pressuring Democrats to drop their support for him.
“My intention is to keep doing what we’re doing, but only to escalate the effort,’’ said David Brog, executive director of the pro-Israel evangelical group Christians United for Israel.
Republicans were moving on other fronts to block Obama as he tries to put together his national security team. Senator Rand Paul of Kentucky has said he will place a hold on the nomination of the director of central intelligence, John O. Brennan, and McCain and Graham also said they intended to use Brennan’s nomination to force the administration to answer questions about the September attack in Benghazi, Libya.
In a statement after Thursday’s vote, the White House accused Republicans of putting ‘‘political posturing ahead of our nation’s security.’’ It added that there were serious matters at hand: ‘‘We have 66,000 men and women deployed in Afghanistan, and we need our new secretary of defense to be a part of significant decisions about how we bring that war to a responsible end.’’
The Pentagon said Defense Secretary Leon E. Panetta will remain in the position.