Obama expected to nominate Ashton Carter to lead Pentagon
Ashton Carter walks towards his seat at the start of a meeting with Japanese Senior Vice Defence Minister Shu Watanabe (not pictured) in Tokyo July 20, 2012. REUTERS/Yuriko Nakao

U.S. President Barack Obama is expected to nominate former Pentagon official Ashton Carter as U.S. defense secretary, CNN reported on Tuesday.

Carter, a former deputy secretary at the Department of Defense, had been considered a leading candidate for the job to replace Chuck Hagel, who is resigning.

A Pentagon spokesman said he was unaware of a decision and referred reporters to the White House, which had no immediate comment on the report. A spokeswoman for Carter also had no immediate comment.

Other names have been circulated as a possible replacement for Hagel, including former Navy Secretary Richard Danzig and Kurt Campbell, a former Assistant Secretary of State for East Asian and Pacific Affairs who now heads the Asia Group, a strategy and capitol advisory group.

Homeland Security Secretary Jeh Johnson, a former general counsel at the Pentagon who had been believed to be under active consideration, took himself out of consideration, according to a source familiar with the situation.

Carter was the No. 2 official at the Pentagon from October 2011 to December 2013. Previously, he was the Pentagon's chief arms buyer.

He also served as assistant secretary of defense for international security policy under President Bill Clinton.

Carter has bachelor's degrees in physics and medieval history from Yale, a doctorate in theoretical physics from Oxford University, where he was a Rhodes scholar, according to the Pentagon website.

Hagel resigned under pressure last week after less than two years at the helm of the Defense Department.

(Reporting by Steve Holland, Andrea Shalal and Bill Trott; Writing by Susan Heavey; Editing by Doina Chiacu and Jeffrey Benkoe)