Senate Republicans blocked a vote on Chuck Hagel’s nomination as secretary of defense on Thursday, launching an unprecedented filibuster and a severe rebuke to the White House.

Falling one vote shy of the 60 needed to move forward on the nomination, the Hagel filibuster brought stark condemnations from President Obama and Senate Democrats for its precedent-setting nature -- the first time a defense secretary nominee had been filibustered. The setback came during what many believe is a critical period for the Pentagon as it winds down troops from Afghanistan and implements costly budget cuts.

It was also a hard slap to a former colleague and member of the chamber.

Asked about the Senate vote during an online “fireside hangout,” Obama said that he expects that Hagel will be confirmed. But he slammed Senate Republicans for their “unprecedented filibuster” of a defense chief nominee.

“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,” Obama said. “Well, that’s not the rule.”

He added that “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” on U.S. strategy in the region.

Republicans predicted they would relent to a simple majority vote, guaranteeing confirmation, later this month -- but only if they see more information about Hagel’s post-Senate foreign policy speeches and his work in private investment groups. Senior Republicans initially scoffed at those demands, first raised by freshman Sen. Ted Cruz (R-Tex.), as unnecessary, but now party leaders hold them up as the main cause for delay.

Even if Hagel is eventually confirmed, the process marked another escalation in long-running nomination wars dating to the 1980s, now crossing into an area that has long been the most bipartisan on Capitol Hill: national security.

The Hagel fight also demonstrated the Republican fixation on the events surrounding the Sept. 11 attack on the U.S. consulate in Libya that killed four American diplomats. GOP senators have clung to the tragedy as cause for holding Hagel’s nomination hostage in exchange for more details about the attack.

Such demands are commonplace in the Senate but are usually reserved for lower-level Cabinet posts or for deputy-secretary positions, not for the person who is in charge of overseeing more than 2 million service members — 66,000 of them in battle in Afghanistan.

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

The final tally Thursday was 58 votes to end the filibuster to 40 against, but actually 59 backed Hagel because Reid changed his vote to no so that he could use parliamentary rules to quickly reconsider the nomination when the Senate returns from its Presidents Day break Feb 25.

Reid called for the vote Thursday, despite pleas by several Republican senators to delay the vote until after the holiday recess. By calling the vote, Reid set up the Senate to block President Obama’s choice to lead the Pentagon, a stinging slap at a former colleague and member of that chamber.

Reid had initially called for a vote on Friday -- which Democrats and Republicans then agreed should be sped up to Thursday -- to highlight what Reid sees as unprecedented Republican obstruction. Democrats said the Republican push for a delay, even a brief one, was designed to allow more time to bloody the nominee and that, in fact, the GOP will never be satisfied with the amount of information released about Hagel.

Democrats said they also pressed ahead with a vote to fill the Cabinet position quickly, as Defense Secretary Leon E. Panetta steps down and heads to California. But Democrats conceded that if Hagel is blocked, they will try again after the recess.

“If we don’t bring it to an end today, then there will be another vote a week from Tuesday,” Sen. Carl Levin (D-Mich.), chairman of the armed services committee, said before the vote. But, he added, “the world is too dangerous to have this period of uncertainty.”

Earlier Thursday, Reid announced that Republicans had secured enough votes to mount a filibuster on the confirmation.

But a number of Republicans who believe it is bad precedent for a defense secretary nominee to face a 60-vote threshold said they would be willing to vote to end debate on the nomination if the White House provided further answers to several lingering questions.

Democrats can return to the issue after next week’s recess, when a number of leading Republicans have said they will vote to close off debate, allowing the Senate to move ahead to an up-or-down vote on the nomination, requiring only 51 votes for confirmation.

“I think that during the break is sufficient time to get any additional questions answered,” Sen. John McCain (R-Ariz.) said before the vote Thursday. “And I will vote for cloture on the day we get back, and I believe that enough of my colleagues would do the same,”

Sen. Lamar Alexander (R-Tenn.) told reporters that cutting off debate is “premature.”

“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,” Alexander said. “I know of many of my colleagues who think that’s enough time. It would be better for the institution and the country if we had enough time to consider Senator Hagel and then have an up-or-down vote, so we don’t get into a habit of making it look like we’re suing the filibuster to block Cabinet nominees. That’s not the case here.”

Earlier in the day, Democratic aides confirmed that senior Republicans told them late Wednesday that GOP leaders had at least 41 Republicans to block the planned Friday vote. A senior GOP aide confirmed that some Republicans who had publicly opposed filibustering what has traditionally been a key national security post with bipartisan support were now withholding their votes for answers from the White House.

“The members still await the information they want,” the senior aide said, who spoke on the condition of anonymity to discuss Minority Leader Mitch McConnell’s leadership team deliberations.

Speaking immediately after Reid in the morning, McConnell (R-Ky.) ignored mentioning a filibuster and instead focused his remarks on the automatic spending cuts set to hit March 1 — which will include $46 billion slashed from the Pentagon’s 2013 budget.

Leading Republicans, including McCain, have said they would drop the filibuster effort if the White House gives them more information about the actions President Obama took during an eight-hour siege at the U.S. mission in Benghazi, Libya, on Sept. 11. The attack killed the U.S. ambassador to the country and three other Americans.

Democrats, however, have suggested that Republicans are only focusing on Benghazi to slow the confirmation process so that Hagel — known for a mercurial temperament and as an impulsive decision-maker in the past — would withdraw his nomination.

A spokesman for Hagel suggested he would stay and fight, as did a spokesman for the president, who was flying to a domestic policy event in Georgia.

“We urge the Republicans in the Senate to drop their delay,” Obama spokesman Josh Earnest said. “There is a clear majority in the United States Senate for senator Hagel’s confirmation. These delaying tactics are unconscionable, and they should end right away.”

White House counsel Kathryn H. Ruemmler sent McCain a letter Thursday that largely reiterated the facts found by an accountability review board that examined the Benghazi attack. She added that then-Secretary of State Hillary Rodham Clinton was in contact with the Libyan leadership during the attack “to coordinate additional support to protect Americans” there, noting that Obama called the Libyan president the next day to discuss the security situation in the area.

“We continue to urge the full Senate to act swiftly and confirm senator Hagel,” Ruemmeler wrote.

McCain said Thursday that he was satisfied by the White House response to his question but that he believes other senators still have pending inquiries.

“We are working on and having negotiations now, trying to smooth this thing out and get it done,” McCain said. “I have said all along that we had to have the concerns of senators addressed. I’m hopeful that we can get those concerns addressed and still move forward with a 51-vote vote, because we have never required 60 votes on a secretary of defense.”

On the Senate floor Thursday morning, Reid warned forebodingly that if Hagel was not confirmed Friday, the Pentagon would be without an official leader.

“In less than two hours, our country will be without a secretary of defense,” Reid said. “It’s shocking that my Republican colleagues would leave the nation without a fully empowered secretary of defense.”

The Pentagon says otherwise. Defense Secretary Panetta “believes Senator Hagel should be confirmed as quickly as possible, and plans to stay in office until he is confirmed,” Pentagon spokesman George Little said.

Panetta did little to hide his frustration Thursday about Hagel’s embattled nomination. Hosting former secretary of state Hillary Clinton at the Pentagon for what Panetta had hoped would be his last day on the job, he said he was counting the days until he flies home to California— for good.

After calling Clinton’s visit a “great Valentine’s Day present for all of us here,” Panetta joked that there was one more item 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,” Panetta said, referring to his wife. “I feel like it’s “Groundhog Day” around here.”

During his time on the Senate floor Thursday, Reid slammed Republicans for demanding more information on Benghazi from Hagel and the White House, calling claims that Hagel had not been forthcoming in his testimony during his confirmation hearing “outlandish.”

Rachel Weiner, Rosalind S. Helderman, Ernesto Londoño and Felicia Sonmez contributed to this report. Discuss this topic and other political issues in The Post’s Politics Discussion Forums.