WASHINGTON >> Former Pentagon official Ashton Carter is likely to be President Barack Obama’s nominee for defense secretary, according to administration officials, putting him in line to take over a sprawling department that has had an uneasy relationship with the White House.

Obama spokesman Josh Earnest stopped short of confirming the president’s decision, yet praised Carter effusively for serving “very, very ably” at the Pentagon previously and noted he had been easily confirmed by the Senate once before.

“This is an indication that he fulfills some of the criteria that we’ve discussed in the past,” Earnest said. “He is somebody who definitely deserves and has demonstrated strong bipartisan support for his previous service in government.”

Administration officials said Obama could announce his nominee as early as this week, though he was not expected to do so Tuesday. The officials insisted on anonymity because they were not authorized to discuss the president’s decision-making process publicly.

A physicist with deep Pentagon experience, Carter moved to the top of the White House’s short list after several leading contenders pulled their names from consideration for what is typically a highly sought-after Cabinet spot. If Obama moves forward with Carter’s nomination and he is approved by the Senate, the 60-year-old would replace Chuck Hagel, who resigned as Pentagon chief last week under pressure from Obama.

Hagel’s resignation highlighted ongoing tensions between the White House and the Pentagon, where top officials have complained about West Wing micromanagement and a lack of clarity in Obama’s policy-making. Perhaps as a result of those concerns, Obama found himself with a far shorter list of possible replacements for Hagel that the White House may have expected.

Homeland Security Secretary Jeh Johnson was among those considered for the Pentagon post, but told the White House he’d rather stay put, according to people familiar with the process. Michele Flournoy, one of Obama’s top choices, quickly took her name out of contention, in part because of concerns over the tight rein the White House has tried to keep on the Defense Department. And Sen. Jack Reed, a Rhode Island Democrat and West Point graduate, also made clear within hours of Hagel’s resignation that he wasn’t interested.

Sen. Jim Inhofe of Oklahoma, the Senate Armed Services Committee’s top Republican, said he was informed Tuesday morning that Obama was to nominate Carter and that he backs the expected nomination. An aide of Inhofe said later the senator had based his comments on press reports.

“I support it very strongly,” Inhofe said of Carter’s probable nomination. “I’m very pleased he is going to be our secretary of defense. I can’t imagine that he’s going to have opposition to his confirmation.”

Defense analyst Anthony Cordesman said that as Obama approaches the end of his presidency, the Cabinet post is “not particularly desirable” for anyone with broader political ambitions.

“It’s very unlikely you will get political visibility or credit for being the secretary,” said Cordesman, who works at the Center for Strategic and International Studies. “There are just too many problems and uncertainties.”

Among them: questions about the effectiveness of Obama’s military campaign against the Islamic State in Iraq and Syria, Russia’s continued provocations in Ukraine, tensions between the White House and Defense Department over closing the Guantanamo Bay, Cuba, detention center, and concerns at the Pentagon over the impact of deep spending cuts.

Hanging over all of those policy concerns is the uneasy relationship between the White House and the Pentagon throughout Obama’s six years in office. His first two defense secretaries, Robert Gates and Leon Panetta, have been bitingly critical about White House efforts to micromanage the Pentagon. And Hagel is said to have grown frustrated by the White House’s drawn-out policymaking process and lack of clarity in the president’s eventual decisions.

Lawrence Korb, a former assistant defense secretary, said that with just two years left in Obama’s presidency, the next Pentagon chief will be hamstrung in efforts to shape the administration’s policies and the department’s relationship with the White House.

“The clock is ticking in terms of being able to make significant changes,” said Korb, a senior fellow at the Center for American Progress, a think tank closely aligned with the White House.

Carter has extensive experience in the national security arena. Before he served as deputy defense secretary from October 2011 to December 2013 he was the Pentagon’s technology and weapons-buying chief for more than two years.

“He’s a technocrat and a good manager,” said Jane Harman, a former California congresswoman and now president of the Wilson Center. “He knows the acquisitions side of the building and has impressed the military with his commitment to the troops.”

Carter 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. He has extensive knowledge of the inner workings of the U.S. nuclear arsenal.

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AP National Security Writer Robert Burns and AP writer Donna Cassata contributed to this report.