Senate Republicans delivered a sharp rebuke to President Obama on Thursday when they began a filibuster of Chuck Hagel’s nomination as secretary of defense.

The confirmation process stalled Thursday when GOP senators deprived Hagel of the 60 votes needed to move it to its final stages. Republicans said they were seeking a delay so they could look more closely at the nominee.

Both sides still think the former GOP senator from Nebraska will be confirmed, but the filibuster brought stark condemnations from Obama and Senate Democrats, who decried it as an unprecedented partisan move against a nominee to lead the Pentagon.

The move was one more signal of how times have changed in the once-clubby Senate. Democrats say they think that some senior Republicans facing reelection in 2014 are so fearful of conservative primary challenges that they will ignore the bipartisan traditions of the Senate to be more in line with junior GOP senators elected on the strength of tea party affiliations. The result is that hoped-for bipartisan deals on such issues as immigration and budget matters could be harder to reach.

“It’s just unfortunate that this kind of politics intrudes at a time when I’m still presiding over a war in Afghanistan and I need a secretary of defense who is coordinating with our allies,” Obama said Thursday in an online forum hosted by Google.

“What seems to be happening, and this has been growing over time, is the Republican minority in the Senate seems to think that the rule now is that you need to have 60 votes for everything. Well, that’s not the rule.”

Republicans denied that their actions constituted a filibuster because they expect Hagel to be confirmed, and they insisted they will allow a simple-majority vote on the nomination later this month.

They said they stalled the nomination because they want more information about Hagel’s post-Senate career, including foreign policy speeches he delivered and his work with private investment groups.

The clash marked an escalation in nomination wars dating to the 1980s, crossing into an area that has most retained an aura of bipartisanship on Capitol Hill: national security.

The Hagel fight also demonstrated the depth of ongoing Republican concerns about the Sept. 11 attack on a U.S. diplomatic mission in Benghazi, Libya, that killed four Americans, including Ambassador J. Christopher Stevens. Several GOP senators initially said they wanted more information about the attacks in exchange for approving the nomination.

Such demands are not uncommon, but they usually involve delaying confirmation for lower-level Cabinet posts or deputy secretary positions while senators seek information or rulings on regulations from the White House.

“This isn’t high school, getting ready for a football game or some play that’s being produced at high school. This is — we’re trying to confirm somebody to run the defense of our country, the military of our country,” an angry Senate Majority Leader Harry M. Reid (D-Nev.) said in a floor speech Thursday morning.

Reid accused senior Republicans of being “worried about primary elections” in which tea party conservatives would challenge them for not trying hard enough to block Obama’s Pentagon nominee.

The official tally Thursday was 58 votes to end the filibuster to 40 against doing so, but 59 initially backed Hagel — Reid changed his vote to “no” so he could use parliamentary rules to quickly reconsider the nomination. Four Republicans — Sens. Thad Coch­ran (Miss.), Susan Collins (Maine), Mike Johanns (Neb.) and Lisa Murkowski (Alaska) — joined 54 members of the Democratic caucus in voting to end the filibuster.

Another Hagel vote is scheduled for Feb. 26, when the Senate returns from a 10-day break. That vote is also likely to require 60 votes to move to confirmation.

But senior Republicans said that their Thursday blockade probably will be over by then and that they will allow confirmation at some point.

Minority Leader Mitch Mc­Connell (R-Ky.) — who has gone several days without saying anything publicly about Hagel — has deputized Sen. John McCain (R-Ariz.) as the weather vane by which to judge when Republicans should yield on the filibuster.

That has, at times, made it difficult to discern the party’s position.

On Monday, when some GOP strategists were pondering a walkout of the Armed Services Committee's consideration of Hagel, McCain issued a statement declaring that the nominee “has fulfilled the rigorous requirements that the committee demands” and that he deserves a committee vote.

During Tuesday’s committee hearings, Sen. Ted Cruz (R-Tex.) demanded more information on Hagel’s speeches, suggesting that the nominee could have received money from nefarious sources such as North Korea. That prompted McCain to lecture Cruz that “no one on this committee at any time should impugn his character or his integrity.”

By Tuesday night, after voting against Hagel in committee, McCain joined Sens. Lindsey O. Graham (R-S.C.) and Kelly Ayotte (R-N.H.) in writing the White House, threatening to filibuster unless more information about the Benghazi attack was released.

By Thursday, after receiving that information, McCain and others called Cruz’s demands for more information on speeches “reasonable requests” that might turn up new information. “There are other questions that need to be answered, and we feel that the intervening week and a half, almost, is sufficient time to get those questions answered,” he told reporters just before supporting the filibuster.

Republicans do not know whether anything of note is in the speeches, but additional transcripts have been discovered this week. Others said they just need more time to consider a controversial nominee whose performance at a confirmation hearing was widely considered subpar.

“He came out of the committee two days ago,” said Sen. Lamar Alexander (R-Tenn.). “My own view is that cutting off debate today is premature, and I won’t vote for that. When we come back from the recess 10 days from now, senators should have had sufficient time to consider Senator Hagel’s nomination, and I will vote to have an up-or-down vote.”

Democrats called it unnecessary and pointed to an intense vetting process by the FBI and the Senate Armed Services Committee that has provided senators with thousands of pages of information.

“He’s done everything he possibly can,” said Armed Services Chairman Carl Levin (D-Mich.). He called it “inappropriate to suggest the innuendo” from Cruz that Hagel has received money from estranged foreign governments.

Defense Secretary Leon E. Panetta did little to hide his frustration about Hagel’s beleaguered nomination on Thursday, what was supposed to be his last day on the job.

Hosting former secretary of state Hillary Rodham Clinton at the Pentagon, the secretary said he was counting the days to fly home to California — for good.

After calling Clinton’s visit a “great Valentine’s Day present for all of us here,” Panetta said one additional item was on his wish list.

“The second-best Valentine’s present would be to allow Sylvia and I to get the hell out of town at the end of the day,” he said, referring to his wife and then invoking a Bill Murray movie in which the lead character keeps reliving the same day.

“I feel like it’s ‘Groundhog Day’ around here,” the secretary joked.

Hagel’s nomination has taken a similar path to that of Supreme Court Justice Samuel A. Alito in 2006, when Democrats were unable to find incriminating documents. Republicans mocked Democrats after halting a hearing to review material in the Library of Congress relating to Princeton University, his alma mater, coming up with nothing controversial.

Rank-and-file Democrats pressured their leaders into forcing a filibuster vote, but 19 Democrats joined all Republicans to reject a filibuster — 13 of whom then voted against Alito’s confirmation on a vote of 58 to 42.

Rosalind S. Helderman, Ernesto Londoño, Ed O’Keefe and Felicia Sonmez contributed to this report.