WASHINGTON (AP) _ President Barack Obama announced Monday that chief of staff William Daley was quitting and heading home to Chicago, capping a short and rocky tenure that had been expected to last until Election Day in November. Obama budget chief Jack Lew will take over the job.

Daley's run as Obama's chief manager and gatekeeper lasted for all of one consequential year _ filled with notable moments like the killing of al-Qaida terrorist leader Osama bin Laden, but also internal grumbles that the top aide had not turned out to be the right fit to coordinate an intense operation of ideas, offices and egos.

Obama said he took the news reluctantly, initially refusing to accept Daley's resignation letter last week and ordering him to think it over. Daley stood by the decision, expressing a desire to be with his family and return to Chicago.

Yet he offered no explanation on Monday about what accelerated his decision; Daley had committed to Obama that he would stay on through the election. Obama senior adviser Pete Rouse had already taken on more of the day-to-day management of the White House, trimming Daley's portfolio amid West Wing struggles over coordination and communication.

``No one in my administration has had to make more important decisions more quickly than Bill, and that's why I think this decision is difficult for me,'' Obama said to a nearly empty State Dining Room, other than mainly the assembled media.

Lew and Daley stood by the president but did not speak. The White House said neither man was giving interviews.

Obama now plows ahead into an election year with his third chief of staff _ one of the most influential and demanding jobs in U.S. government and politics.

Daley had come aboard last January to replace the colorful and involved-in-everything Rahm Emanuel, who left the job to run for Chicago mayor, a position he now holds.

The transition from Daley to Lew is expected to take place at the end of the month. Just ahead for Obama are two crucial, tone-setting events: his State of the Union speech on Jan. 24 and the release of his budget proposal in early February.