President Barack Obama plans to name White House Chief of Staff Jack Lew tomorrow as his choice for Treasury secretary, replacing Timothy F. Geithner, a person familiar with the process said.

Lew, 57, who also has served as director of the Office of Management and Budget, has been offered the Treasury post by Obama, according to the person, who asked for anonymity to discuss personnel matters.

Geithner, 51, the only remaining member of Obama’s original economic team, has told White House officials he doesn’t want to serve in a second term and intends to leave the job by the end of the month.

Lew’s nomination as Treasury secretary is subject to confirmation by the Senate. While his relations with Republicans have been at times strained, he’s successfully been through the Senate process before.

His prospects for confirmation are “extraordinarily high,” and Lew might get 85 votes in the 100-member chamber, said Stan Collender, a former staff member of the Senate and House budget committees and now a partner at Qorvis Communications in Washington.

Debt Ceiling

The next Treasury secretary will play a leading role in working with Congress to raise the government’s $16.4 trillion debt ceiling. The U.S. reached the statutory limit on Dec. 31, and the Treasury Department began using extraordinary measures to finance the government. It will exhaust that avenue as early as mid-February, the Congressional Budget Office says.

“Your big job is to see the big picture and obviously to protect the president’s behind,” Collender said. “He’s got the big view, he’s got the president’s trust.”

In the next 18-24 months, lawmakers will also consider overhauling the tax code and the entitlement programs that consume hundreds of billions in the budget each year.

“Social Security, Medicare and taxes fall directly into the Treasury secretary’s purview,” Collender said. “You got to look at this job as not just being secretary of the Treasury but being the chief economic policy maker. And that’s what he brings.”