File Photo: US President Barack Obama at the White House in Washington. (AP Photo)
President Barack Obama will announce his choice to replace Chuck Hagel as Pentagon chief on Friday, the White House said.
Favored for the post is Ashton Carter, a former deputy defense secretary under Leon Panetta from October 2011 to December 2013.
While stopping short of confirming the pick, the White House has hailed Carter's "detailed understanding" of the Pentagon's inner workings, and recalled that the Senate had unanimously confirmed his nomination as the Defense Department's number two in 2011.
However, said White House spokesman Josh Earnest: "It's actually the president's nominee, and he will announce it tomorrow."
Hagel, the outgoing Pentagon chief, announced his resignation last week. Officials privately said he was forced out after losing the confidence of the White House, as the United States wages an air war against Islamic State jihadists in Iraq and Syria.
Carter, 60, has gained a reputation as an expert on hi-tech weapons and military budgets, portraying himself as a reformer intent on making the vast Pentagon bureaucracy more efficient.
While Carter is fluent with weapons programs and technological trends, he has less experience overseeing war strategy and has never served in uniform -- unlike his predecessor, Hagel, who was wounded in the Vietnam War.
When Carter stepped down last year, officials denied reports he had clashed with Hagel.
Former number three Pentagon official Michele Flournoy has taken herself out of the running for a post that would have made her the first woman to lead America's military. She cited family reasons.