UPDATE 1-Obama to nominate Lew as Treasury chief Thursday-source

WASHINGTON, Jan 9 (Reuters) - U.S. President Barack Obama will nominate White House chief of staff Jack Lew as his next Treasury secretary on Thursday, replacing Timothy Geithner, according to a source familiar with the matter.

Lew had been widely expected to be tapped for the role. He has served as budget director for Obama and for former President Bill Clinton.

The 57-year old policy wonk, who was a State Department deputy early in Obama's first term, will have to confront a host of tricky economic topics if he wins Senate confirmation, ranging from how best to scale back the government's role in the housing market to how to respond to China's growing economic heft.

The White House sees Lew as well-placed to guide U.S. economic policy domestically and internationally after experience as a member of the executive branch and as a congressional staffer.

Lew helped lead budget talks with Congress under Clinton and spearheaded the "Budget Control Act" negotiations under Obama.

Geithner, a key member of Obama's economic team for years who was a top negotiator in the "fiscal cliff" talks with congressional leaders, had made clear he wanted to step down at the end of the president's first term.

That will leave Lew to deal with the next set of fiscal fights, notably a looming battle over the debt ceiling. Congress must raise the $16.4 trillion debt ceiling limiting how much the Treasury cab borrow by the end of February or risk a damaging debt default.

Then on March 1, deep automatic spending cuts to defense and a wide swath of domestic programs start to go into effect unless Congress acts to soften the blow.

And at the end of March, a stop-gap funding measure expires and the government could be forced to shut down if Congress does not approve another bill to fund federal operations.