The most senior woman to have ever served at the Pentagon, Michele Flournoy, plans to step down from her policy post to spend more time with her family, officials said Monday.

Flournoy, undersecretary of defense for policy, "has today announced her intention to step down and return to private life," Defense Secretary Leon Panetta said in a statement.

Flournoy, who turns 51 this week, "made clear that her decision to leave is motivated by personal and family considerations," the statement said.

Both Flournoy and her husband, who has worked as deputy secretary of veterans affairs, had held demanding jobs in the government since President Barack Obama took office in February 2009 and were ready to restore balance in their life with more time devoted to their three children, spokesman Douglas Wilson told AFP.

Flournoy has agreed to stay on through "early next year" to allow time to find a successor for the number three civilian post in the Pentagon, according to Panetta.

Widely credited with playing an influential role in hammering out defense policy under Obama's presidency, she leaves office as US troops depart Iraq and amid plans to gradually draw down the roughly 97,000 American forces in Afghanistan.

Unlike some controversial figures who have held the job, including Douglas Feith under former president George W. Bush, Flournoy spoke in measured, pragmatic terms in her public appearances and built consensus behind the scenes.

Flournoy has been "an invaluable advisor" and helped guide Obama's approach to the wars in Iraq and Afghanistan as well as a strategy review underway that will shape defense budget cuts, Panetta said.

"Michele has made a strong and lasting positive imprint on this department and on our nation's security," Panetta's statement said.

Flournoy has often been mentioned as a possible candidate for the top job and she may get the chance if Obama wins re-election and Panetta retires as expected.

Flournoy hoped to help with Obama's re-election effort but does not intend to take any formal position in the campaign, officials said.