The Senate Armed Services Committee vote was left open for 10 minutes to allow a Republican senator, David Vitter of Louisiana, who was not present and left no instructions, to return and make his views known. He did not return, but his vote would not have changed the outcome.
Democrats control 14 votes on the committee, including Sen. Angus King, Ind-Maine. Democrats also control a majority in the full Senate, 55.
The committee's ranking member, Sen. James Inhofe, R-Okla., unsuccessfully asked that the vote be delayed until GOP questions are answered.
Sen. Lindsey Graham, R-S.C., was one of Hagel's strongest opponents. "The next secretary of defense will have to deal with a world on fire," Graham said, "and I believe Sen. Hagel's [earlier] testimony was not reassuring."
Republicans have contended Hagel's past statements showed him as soft on Iran and antagonistic toward Israel.
Democrats and Republicans butted heads before the vote in uncharacteristically harsh language.
Sen. Ted Cruz, R-Texas, repeatedly tried to suggest Hagel, a former Republican senator from Nebraska, may have received payments from foreign sources, but said he had no evidence because Hagel refused to answer questions about his income.
"We do not know for example if he received compensation for paid speeches at extremist or radical groups," Cruz said. "It may be that he received extraordinary payments from defense contractors. ... I don't know if Chuck Hagel has received compensation from foreign or extremist sources."
Committee Chairman Carl Levin, D-Mich., pointed out that when asked in writing by the Senate Armed Services committee whether he and his wife had received money from a foreign government or an entity controlled by a foreign government in the last 10 years, he answered "no."
Sen. Bill Nelson, D-Fla., went further, saying, "Senator Cruz has gone over the line. He basically has impugned the patriotism of the nominee."
Cruz denied doing so, saying he had earlier praised Hagel for his service as an enlisted soldier in Vietnam.
"My point is not that he has lied; it is that he has refused to answer reasonable questions," Cruz said.
Sen. John McCain, R-Ariz., who indicated he will vote against confirmation, said Hagel "is an honorable man. No one on this committee should impugn his integrity."
Hagel will almost surely win Senate confirmation as defense secretary, the White House said ahead of the committee vote.
"We believe firmly that Senator Hagel will be confirmed as the next secretary of defense," White House spokesman Jay Carney said.
Hagel, 66, faced sharp and sometimes angry questioning from fellow Republicans, especially former ally McCain, at his confirmation hearing Jan. 31.
McCain and Hagel are both decorated Vietnam veterans and Hagel was co-chairman of McCain's 2000 presidential campaign.
The confirmation hearing focused on past Hagel statements about Iran, the influence of pro-Israel organizations in Washington and the Iraq war, whose surge Hagel did not support.
"Since his hearing, we have seen an increase in the number of senators who have come out and said that they will vote to confirm him," Carney said. "That includes Republicans as well as Democrats. And we look forward to his hearing and to a vote on the floor."
The full Senate vote could come as early as Wednesday, said Senate Majority Leader Harry Reid, D-Nev.
Last week, 25 Republican senators sent Levin a letter demanding Hagel turn over more financial information before they would consider a vote.
They said they wanted to know if he or organizations he has been involved with have received funding from foreign sources.
Levin said in response it would be unprecedented for a nominee to produce more financial information than Hagel already provided.
As action drew closer, Republican opponents, most notably Graham, threatened filibusters and even a walkout from the vote unless their evolving demands were met.
The new demands included more information from the White House about the Sept. 11, 2012, attack on the U.S. Consulate in Benghazi, Libya, and a sexual harassment allegation involving two former staff members but not Hagel himself.
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