Senate Republicans, who have been mostly deferential to Obama's nominees, were blocking efforts to fast-track Geithner's nomination, with at least one Finance Committee member saying the tax questions deserved greater scrutiny.
Obama had hoped for approval by Tuesday, but given the GOP objections, senators scheduled Geithner's confirmation hearing for next Wednesday, with Senate debate and a vote sometime after that.
Two Republicans formally objected to scheduling the hearing this Friday after the panel disclosed that Geithner had failed to pay some taxes he owed between 2001 and 2004.
"Look, is this an embarrassment for him? Yes. He said so himself. But it was an innocent mistake," Obama said. "My expectation is that Tim Geithner will be confirmed."
Obama spoke at his transition office after a meeting with Vice President-elect Joe Biden and Sen. Lindsey Graham, R-S.C., about a recent trip to Afghanistan, Pakistan, Iraq and Kuwait.
A number of Democrats and Republicans on the Finance Committee voiced strong support for Geithner, who was phoning senators individually in an effort to persuade them his tax problems were the result of innocent errors, not deliberate attempts to avoid paying the Internal Revenue Service.
Senators' reactions suggested they viewed his missteps more as embarrassing mistakes than as disqualifying misdeeds. That's despite the fact that tax problems have helped sink other government nominees, including Zoe Baird, Bill Clinton's choice for attorney general, who stepped aside when word leaked that she had hired illegal immigrants as household workers and failed to pay their Social Security taxes.
"It's an honest mistake," said Sen. Max Baucus, the Montana Democrat who chairs the committee, adding that confirmation was "a given" for the man who would move to Washington from his position as president of the New York Federal Reserve.
Geithner is "very, very competent, and add to that the country needs to have an economic team in place immediately to address the dire economic problems," he said.
Sen. Jon S. Kyl of Arizona, the committee's No. 2 Republican, blocked the hearing by insisting on rules that require a full week's notice for scheduling, according to an aide close to the confirmation process. A second committee Republican, Jim Bunning of Kentucky, was also balking.
"Senator Bunning did not feel it was appropriate to rush forward with the hearing this week in light of the late-breaking information," said his spokesman, Mike Reynard. "He wanted more time to carefully consider" the disclosures.
But other Republicans said their party had little appetite for a fight over Geithner at a precarious time for the econom this administration for treasury secretary," he said.
And John Ensign, R-Nev., who said he spoke with Geithner for about a half-hour on Wednesday, said he didn't foresee trouble for the nominee. "It's very, very easy to make honest mistakes," he said.
Pat Roberts, R-Kan., said he probably would vote to confirm Geithner.
Obama's team informed Baucus and Grassley of the problems in early December, and a subsequent investigation by their staffs unearthed another embarrassing detail about Geithner: that a housekeeper he employed in 2005 allowed her legal immigrant work status to lapse for three and a half months.
It was the unpaid taxes, though, that were proving more of a problem. Obama's team says his mistake was a common one for people hired by international organizations and foreign embassies that don't pay the employer share of Social Security taxes. The IRS estimated in 2006 that as many as half those employees had made tax-filing mistakes, and offered a group settlement to let them correct the errors.
But the Finance Committee, in 30 pages of documents released on Tuesday, noted that the IMF issues several clear guidelines each year for its employees detailing their responsibility to pay all their self-employment taxes, and that Geithner had signed annual statements saying that he would do so. He also had experience dealing with such taxes, the panel noted.