David Jackson and Tom Vanden Brook

USA TODAY

WASHINGTON — Former Pentagon official Ashton Carter is the top candidate to replace outgoing Defense Secretary Chuck Hagel and could be nominated this week, officials said Tuesday.

Carter, a physicist, served as deputy Defense secretary, and has extensive knowledge of the Pentagon's inner workings, said the officials, who spoke on condition of anonymity because the decision was not final.

The officials said Carter is the leading candidate but that the vetting process is not complete and that President Obama has not yet made the final sign-off.

White House spokesman Josh Earnest said Carter performed "very, very ably" as deputy secretary of Defense. He also noted that the Senate confirmed Carter in that job by unanimous consent.

"This is an indication that he fulfills some of the criteria that we've discussed in the past" for the Pentagon post, Earnest said. "He is somebody that does have detailed understanding of the way that the Department of Defense works."

A s for when Obama might make an announcement, Earnest said: "I don't have an update."

Rear Adm. John Kirby, the Pentagon spokesman, said Tuesday the announcement of a successor to Hagel is something only the White House can make.

Carter stepped down as the deputy secretary of Defense on Dec. 4, 2013. He had served as the top deputy to Hagel and his predecessor, Leon Panetta.

"Of course there's all kinds of rumors that he's going to be nominated. I've had a long-standing relationship with him, going back to the Clinton years. He is a fine man. He's certainly qualified for the job. But let's wait till the nomination gets here," Senate Majority Leader Harry Reid, D-Nev., told reporters Tuesday.

He had been considered a leading candidate to replace Panetta but Obama opted for Hagel. Carter served as deputy secretary of Defense from October 2011 until his retirement in December 2013. His specialties include science, technology and developing the defense budget in tight economic times.

From 2009 to 2011, Carter — a Yale graduate with a degree in physics — served as undersecretary for acquisition, specializing in procuring equipment to meet emerging threats.

Before he left the Pentagon, Carter was the military's top weapons' buyer and pushed hard for gear that troops needed to stay alive on the battlefields in Iraq and Afghanistan: Mine Resistant Ambush Protected (MRAP) vehicles to protect them from roadside bombs, surveillance equipment to spy on insurgents and bomb-sniffing dogs to find the buried mines that killed and maimed troops on foot patrols.

Regarded as capable, brainy and wonkish, Carter, toward the end of his tenure, led the Pentagon review of its budget as the days of unconstrained spending came to an end. In fiscal year 2001, adopted before the 9/11 terror attacks, the Pentagon's budget was $297 billion. Ten years later, it had ballooned to $687 billion, including funding for the wars in Iraq and Afghanistan.

Carter, in an interview with USA TODAY shortly before retiring in 2013, said that Pentagon budget writers had developed a mind-set prompting them to solve "problems with money rather than using other managerial tools."

Carter pointed to compensation for troops as an area of potential saving. Reforming the Pentagon's pay and retirement systems has been difficult politically. But outside observers, such as Todd Harrison at the Center for Strategic and Budgetary Assessments, say it is vital.

If personnel costs continue growing at the current rate and the overall defense budget remains flat, military personnel costs will eat up the entire defense budget by 2039, Harrison said.

Hagel was charged with overseeing a downsizing at the Pentagon as troops exited Iraq in 2011 and began withdrawing from Afghanistan. Each service has begun trimming troops from the ranks, although the rise of the Islamic State in Iraq and Syria and continued combat in Afghanistan has prompted second thoughts on deep cuts to defense spending. The Republican-led Congress is likely next year to push for greater spending on the military.

Carter would replace Hagel, who resigned under pressure last month.

Carter also worked in the Clinton administration, helping to develop the U.S. nuclear weapons policy after the collapse of the Soviet Union.

Other potential candidates — former undersecretary of Defense Michele Flournoy and Sen. Jack Reed, D-R.I. — withdrew from consideration in the days after Hagel's resignation.

Contributing: Susan Davis