AP Source: Hagel resigning as Pentagon chief, expected to be announced Monday

FILE - In this Thursday, Oct. 30, 2014, file photo, Defense Secretary Chuck Hagel listens to a question during a briefing at the Pentagon. A senior administration official says Secretary of State Chuck Hagel is resigning from President Barack Obama's Cabinet. (AP Photo/Susan Walsh) (The Associated Press)

FILE In this photo taken Tuesday, Sept. 16, 2014, Defense Secretary Chuck Hagel, left, and Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, appear before the Senate Armed Services Committee, the first in a series of high-profile Capitol Hill hearings. Defense Secretary Hagel resigning from Obama Cabinet Monday. (AP Photo/J. Scott Applewhite/File) (The Associated Press)

FILE - In this Oct. 8, 2014 file photo, President Barack Obama, flanked by Defense Secretary Chuck Hagel, left, and Joint Chiefs Chairman Gen. Martin Dempsey, speaks to the media at the conclusion of a meeting with senior military leadership, at the Pentagon. Defense Secretary Hagel is resigning from the Obama Cabinet Monday. (AP Photo/Jacquelyn Martin) (The Associated Press)