Washington - US President Barack Obama on Monday nominated controversial former Republican senator Chuck Hagel to lead the Pentagon and hard-nosed counter-terrorism czar John Brennan to head the CIA.
The second term revamp to two pillars of Obama's national security team is expected to win ultimate Senate approval, although Hagel has been strongly criticized by fellow Republicans for his previous positions on Israel and Iran.
Obama paid particular tribute to retiring Pentagon chief Leon Panetta before giving ringing endorsements to the "outstanding" Hagel and Brennan and urging the Senate not to dally in confirming the important appointments.
"Chuck Hagel is the leader that our troops deserve. He is an American patriot," the president said, heaping praise on the war hero's record, which includes two Purple Hearts for bravery as a soldier in Vietnam.
"He would be the first person of enlisted rank to serve as secretary of defence. One of the few secretaries who had been wounded in war and the first Vietnam veteran to lead the department," Obama said, calling his appointment "historic".
Administration appointments are often tense affairs in the United States as the confirmation hearings provide senators with opportunities to turn away unwanted candidates or score cheap political points, or both.
Hagel, 66, who is known for a fiercely independent streak and a tendency to speak bluntly, is expected to get particularly rough treatment.
Despite the fact that he is a fellow Republican, heavyweights in his party have accused him of hostility toward Israel and naivety on Iran, auguring a tough nomination process ahead.
The top Republican in the Senate, Mitch McConnell, was fulsome in his praise of Hagel when he gave up his Nebraska Senate seat in 2009.
However, speaking on the eve of his nomination, McConnell was far more circumspect, saying only that he was committed to giving his former colleague "a fair hearing like any other nominee".
Although Hagel had a mostly conservative record as a senator, some Republicans have never forgiven him for his outspoken criticism of ex-president George W Bush's handling of the Iraq war.
Republican Senator Lindsey Graham, pointing to Hagel's calls for direct US negotiations with Iran and for Israel to negotiate with Hamas, said he would be "the most antagonistic defence secretary towards the state of Israel in our nation's history".
Another Republican senator, John Cornyn of Texas, said he would oppose the nomination, charging it would be the "worst possible message we could send to our friend Israel and the rest of our allies in the Middle East".
If confirmed by the Senate, Hagel will have to manage major cuts to military spending while wrapping up the US war effort in Afghanistan and preparing for worst-case scenarios in Iran or Syria.
Brennan, 57, may get an easier ride but is sure to face questions over his support for the use of certain "enhanced interrogation techniques" under the Bush administration and for his masterminding of the US drone programme.
The 25-year Central Intelligence Agency veteran, an Arabic-speaking Middle East expert, replaces David Petraeus, who resigned in November after confessing to an extramarital affair with his biographer Paula Broadwell.
Obama highlighted what he called Brennan's incredible work ethic, saying "John is legendary even in the White House" and reminding everyone of a now-famous quote from August 2010.
Asked if he got any down time or was all work and no play, Brennan replied: "I don't do down time."
Trained as a spy, Brennan rose quickly as a counter-terrorism analyst and manager in the Near East and South Asia branch of the agency's intelligence directorate. By 1995, he was executive assistant to George Tenet, the agency's deputy director at the time who later became the agency's longest-serving director.
He also served as interim director of the National Counter-Terrorism Centre from 2004 to August 2005.
Republicans have already shown their ability to derail Obama's preferred cabinet choices.
Unyielding opposition from Graham and two other top Republicans, senators Kelly Ayotte and John McCain, forced UN envoy Susan Rice to abandon her ambition to become the next secretary of state.
Rice, a longtime member of Obama's inner circle, had been a favourite to succeed Hillary Clinton as the nation's top diplomat.
But her role as administration defender over the attack that killed the US ambassador to Libya in Benghazi on 11 September 2012 drew her into a furious row with Republicans keen to dent Obama after his re-election victory.
Rice folded her bid on 13 December and asked Obama not to pick her. A week later the president nominated Senator John Kerry, who is expected to face little Republican resistance, not least because his Senate seat in Massachusetts will now be up for grabs.