WASHINGTON — Michele Flournoy, formerly the Pentagon’s policy chief and among President Obama’s more hawkish advisers, could be in line to become the first woman to lead the U.S. military after Defense Secretary Chuck Hagel’s resignation.

Passed over by Obama for the job 20 months ago, Flournoy heads a short list of candidates to direct the war against the Islamic State in Iraq and Syria, and help Afghanistan fight the Taliban insurgency.

Other contenders include Ashton Carter, until last year the Pentagon’s No. 2-ranked official, and Robert Work, Hagel’s current deputy.

Sen. Jack Reed isn’t interested in the job, a spokesman said Monday. Obama had mentioned Reed on Monday as he recounted a 2008 trip to Afghanistan with the Rhode Island Democrat and Hagel, then a Republican senator from Nebraska.

At the White House, Obama said Hagel would stay on until the Senate confirms a successor. No timeframe was given.

Flournoy, among the most senior female officials in Pentagon history, has a long history with Obama. In 2008, President-elect Obama asked her to co-lead his transition team at the Defense Department.

She then kept a relatively low profile as undersecretary of defense for policy, engaged in efforts to end the war in Iraq, reinvigorate the military campaign in Afghanistan and redesign U.S. defense strategy to deal with severe budget cuts.

Always loyal to the president publicly, Flournoy often played the role of principled objector in closed-doors meetings, differing on matters such as the size and scope of the Afghan surge with Vice President Joe Biden and Tom Donilon, Obama’s former national security adviser.

Her suggestions were often seen as more muscular in approach than those Obama authorized.

When she left office in December 2011, Flournoy cited strains on her family life. She is married and has three children.

At the same time, Flournoy, who is now 53, said she hoped to return to government service one day.

And when Defense Secretary Leon Panetta stepped down after Obama’s re-election, she was among those mentioned for the post. Obama opted for Hagel, however.