WASHINGTON — Former Pentagon official Ashton Carter is likely to be President Barack Obama’s nominee for defense secretary, according to administration officials.

Officials said Obama had not made a final decision on the matter, but Carter had emerged as the top candidate.

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.

Sen. Jim Inhofe of Oklahoma, the Senate Armed Services Committee’s top Republican, said he was told of the decision this morning and backs Carter’s expected nomination.

Administration officials said Obama did not plan to announce his Pentagon pick today and could still go in a different direction.

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.