WASHINGTON -- When President Barack Obama nominates Chuck Hagel, the maverick Republican and former senator from Nebraska, to be his next secretary of defense as early as today, he will be turning to a trusted ally whose willingness to defy party loyalty and conventional wisdom won his admiration both in the Senate and on a 2008 tour of war zones in Iraq and Afghanistan.
The choice of Mr. Hagel, the first Vietnam veteran to be nominated for the post, would add a prominent Republican to Mr. Obama's Cabinet, providing some political cover for the president's plans to exit Afghanistan and make cuts to a military budget that has roughly doubled since the 2001 terrorist attacks.
But Republicans made clear Sunday that they will give Mr. Hagel a rough ride on his path to the Pentagon, questioning his support for Israel, his seriousness about the Iranian nuclear threat and his commitment to an adequate defense budget. And Mr. Obama may also face difficulties from some Democrats who are wary of negative comments that Mr. Hagel made more than a decade ago about gays.
Some Obama aides had doubts about the wisdom of the choice, given Mr. Hagel's frosty relationship with members of his own party, but officials said they were confident that they could corral enough votes from both sides of the aisle to win confirmation in the Senate. White House officials confirmed Sunday that Mr. Hagel was Mr. Obama's pick for the job and said the announcement would come today.
Rather than turning to a defense technocrat, Mr. Obama decided on an independent politician whose service in Vietnam gave him a lifelong skepticism about the commitment of U.S. lives in overseas conflicts. Like Mr. Obama, Mr. Hagel supported the war in Afghanistan but opposed the troop surge in Iraq under President George W. Bush.
Mr. Hagel, 66, served as an enlisted man in Vietnam, won two Purple Hearts and still carries bits of shrapnel in his chest. He was the co-founder of a cellular telephone company and headed an investment banking firm before being elected to the Senate in 1996. He retired in 2009 and now teaches at Georgetown University and serves as chairman of the Atlantic Council, a centrist foreign policy group.
In some ways, Mr. Hagel bears a resemblance to Susan Rice, the ambassador to the United Nations and Mr. Obama's first choice for secretary of state. She withdrew her name from consideration, making way for the selection of Sen. John Kerry.
Ms. Rice, like Mr. Hagel, is a trusted Obama ally who spoke up for him during the 2008 presidential campaign and became a lightning rod for Republican attacks.
"The president wants someone whose judgment he respects on the big questions of war and peace," said Philip Zelikow, a senior State Department official under Mr. Bush and now a member of the President's Intelligence Advisory Board. Mr. Hagel is co-chairman of the board.
The White House is calculating that opposition to Mr. Hagel may be loud but not broad and that, in the end, the Senate will confirm him. Administration officials argued that voting against a Republican war hero to run the Defense Department would not be an easy vote for fellow Republicans, and they are confident that disgruntled Democrats will ultimately not deny their president his choice.
When he took office in 2009, Mr. Obama asked Robert Gates, the defense secretary during Mr. Bush's last two years in office, to remain in his job. But Mr. Gates, a former CIA chief and deputy national security adviser, belonged to the mainstream of Republican defense orthodoxy. Mr. Hagel does not, as was evident in harsh comments from Republicans on Sunday.
Sen. Lindsey Graham, R-S.C., said on the CNN program "State of the Union" that he personally liked Mr. Hagel but considered him "out of the mainstream of thinking on most issues regarding foreign policy."
Senate Minority Leader Mitch McConnell, R-Ky., said on the NBC News program "Meet the Press," "I think there will be a lot of tough questions for Sen. Hagel, but he will be treated fairly by Republicans in the Senate."
For weeks, some Jewish groups sought to dissuade Mr. Obama from choosing Mr. Hagel, who once referred to advocates of Israel as "the Jewish lobby."
Mr. Hagel and his supporters have dismissed criticism of his views on Israel, noting that he voted on several occasions to provide billions of dollars in military aid to the country.