US President Barack Obama is considering former Republican senator Chuck Hagel for the job of defense secretary as he moves towards appointing his second-term cabinet, sources said Thursday.

Obama, who has been close to Hagel since they served together in the Senate, has however not made a final decision on whether to send his friend to the Pentagon to succeed Leon Panetta, an administration source said.

A White House official separately also said that no nominations to Obama's cabinet were expected this week, following a report by Bloomberg News that Hagel was the "likely" nominee and had passed a vetting process.

A decision by Obama to pick a Republican to lead the Pentagon would be seen as an attempt to show bipartisanship, although Hagel is seen as a centrist on foreign policy who has broken with his party on several key issues.

Obama is also wrestling with who to choose as his secretary of state, in a wholesale remaking of his national security team in his second term, with a top contender, UN ambassador Susan Rice, under fierce fire from Republicans.

The president must also find a new head of the CIA, after the former director, retired general David Petraeus, resigned after admitting to an extra-marital affair.

Hagel, a decorated combat veteran who branded then President George W. Bush's Iraq troop surge strategy as the worst foreign policy blunder since Vietnam, served two terms as a Nebraska senator before leaving in 2009.