President Obama plans to announce his pick Friday to lead the Pentagon amid the threat from Islamic State militants in Syria and Iraq, the White House said.
White House press secretary Josh Earnest would not say whom Obama has selected, but administration officials have said former Pentagon official Ashton Carter is expected to replace Defense Secretary Chuck Hagel.
Hagel resigned last month under pressure from the president. He is staying on until his successor is confirmed by the Senate.
Other tough issues facing the next defense secretary include Russia's continued provocations in Ukraine, tensions between the White House and Defense Department over closing the Guantanamo Bay, Cuba, detention center, concerns at the Pentagon over the impact of deep spending cuts, responding to the Ebola outbreak in Africa and addressing reports of sexual assault in the military.
Carter, 60, was deputy defense secretary from 2011-2013 and previously was the Pentagon's technology and weapons-buying chief. He has extensive knowledge of the inner workings of the U.S. nuclear arsenal. He has bachelor's degrees in physics and medieval history from Yale University and received his doctorate in theoretical physics from Oxford University, where he was a Rhodes Scholar. He has served on the advisory boards of MIT's Lincoln Laboratories and the Draper Laboratory.
Carter moved to the top of the White House's short list after several leading contenders withdrew from consideration for what is typically a much-desired Cabinet spot. Hagel's resignation highlighted ongoing tensions between the White House and the Pentagon, where top officials have complained about West Wing micromanagement.
Earnest said the president is commander in chief and that the next defense secretary "will be very clear about what the chain of command is."