WASHINGTON (Reuters) - Timothy Geithner won confirmation as U.S. Treasury secretary on Monday and vowed to act quickly to protect the U.S. economy from the worst financial crisis since the Great Depression. "We are at a moment of maximum challenge for our economy and our country," Geithner said as he was sworn into office shortly after the Senate approved him on a 60-34 vote. Faced with a full-blown crisis, senators largely set aside misgivings about Geithner's failure to pay some taxes earlier this decade in light of his experience in battling the financial storm as head of the New York Federal Reserve Bank, a post he relinquished on Monday. Geithner will immediately start work on a massive overhaul of the $700 billion (501.5 billion pound) U.S. financial rescue program and is expected to propose new efforts to unclogged frozen credit markets within the next two weeks. "At this moment of challenge and crisis, Tim's work and the work of the entire Treasury Department must begin at once," President Barack Obama said as Geithner was sworn in. "We cannot lose a single day because every day the economic picture is darkening, here and across the globe." The new administration, which is already pushing Congress to approve an $825 billion economic stimulus package, may need to go back to lawmakers to ask for more funds to clean up the banking system, possibly through the creation of a government-run "bad bank" to soak up distressed assets. "I don't want to prejudge what the parameters might be or the decisions that might ultimately be made," White House spokesman Robert Gibbs told reporters.