U.S. President Barack Obama on Thursday nominated White House chief of staff Jack Lew to be the nation's new Treasury secretary to replace Timothy Geithner, who had decided to resign after serving in that post for the past four years.

Obama emphasized that Lew, who must be confirmed by the Senate, has substantial experience in budget matters.

Lew also headed the White House Office of Management and Budget between 2010 and early 2012, a post he previously held during Bill Clinton's presidency, where he gained hardcore experience in complex budget negotiations with Congress.

Obama said he trusted that the Senate will confirm Lew in his new post as quickly as possible.

Lew is a "low-key guy who prefers to surround himself with policy experts rather than television cameras," said Obama.

The president thanked Geithner for his work during his first term, when - he said - he had to deal with the financial crisis.

"When the history books are written, Tim Geithner is going to go down as one of our finest secretaries of the Treasury," the president said.

Lew expressed his gratitude and said he was honored by the nomination.

At the relaxed ceremony, Obama joked about Lew's signature, which as that of the Treasury secretary would have to appear on all new currency bills and something that has provoked jokes on the Internet due to his virtually illegible scrawl.

"I had never noticed Jack's signature" and when this was highlighted yesterday in the press, I considered rescinding my offer to appoint him," the president said.

"Jack assures me," Obama added, "that he is going to work to make at least one letter legible in order not to debase our currency, should he be confirmed as secretary of the Treasury." EFE