Deputy Defense Secretary William J. Lynn III is resigning as the second-ranking official at the Pentagon, the Associated Press' Robert Burns reports.
Lynn told brand-new Defense Secretary Leon Panetta of his decision Friday, the day Panetta was sworn in, because Lynn says he doesn't think he can commit to serving until the end of President Obama's first term.
Lynn will stay on until his replacement is picked.
The news comes as Obama continues to reshape his national security team, installing a new defense secretary, CIA chief, and chairman of the Joint Chiefs of Staff.
A Pentagon spokesman said no other senior department officials plan to leave in the near future.
Want to contribute to this story? Share your addition in comments.