He failed to pay self-employment taxes for money he earned while working for IMF from 2001 to 2003, according to materials released by the Senate committee. In 2006, the IRS notified him that he owed $14,847 in self-employment taxes and $1,885 in interest from 2003 and 2004, which he paid after an audit. The IRS waived penalties for those tax years.

Transition officials discovered last fall that Geithner also had not paid the taxes in 2001 or 2002. He paid $25,970 in back taxes and interest for those years several days before Obama announced his choice, the committee documents showed.

Geithner and his supporters have said his mistake was a common one for people hired by international organizations that don't pay the employer share of Social Security taxes. Geithner told Obama's team and senators that an accountant had reviewed his tax returns after Geithner prepared them and didn't discover the problem.

But some tax experts said the problem is not that common.

Tom Ochsenschlager, vice president of tax for the American Institute of Certified Public Accountants, said it would be difficult for someone preparing a tax return for a self-employed person to skip the Social Security and Medicare tax lines.

"It's such a basic mistake that I kind of wonder if we know all the facts," Ochsenschlager said of Geithner's situation.

Geithner filed amended tax returns for 2001 through 2006 after Obama's team reviewed his records.

The committee's materials said Geithner "has experience with Social Security tax issues." He filed the taxes late for his household employees in 1996 for years 1993 to 1995; he incorrectly calculated Medicare taxes for his household employees in 1998 and received an IRS notice; and he received notices from the Social Security Administration and the IRS after not filing 2003 and 2004 forms for his household employees, the report states.

Geithner also said he didn't realize a housekeeper he paid in 2004 and 2005 did not have current employment documentation as an immigrant for the final three months she worked for him, the documents indicated.

One of his housekeepers' legal authorization to work in the United States expired on July 15, 2005, and the person continued to work for Geithner until October of that year, the committee's report states.

Geithner is the second Obama Cabinet choice to face controversy. New Mexico Gov. Bill Richardson withdrew his name on Jan. 4 as Obama's commerce secretary after questions surfaced about a federal investigation concerning contributions and a state contract.

Geithner's tax problem was at least the second time such a situation has touched an Obama appointee. Nancy Killefer, the management consultant selected last week to become the new administration's chief performance officer, failed to pay unemployment compensation taxes, apparently on household employees. In 2005, the District of Columbia placed a $946.69 tax lien on her home over the unpaid taxes. Over a year and a half, she had failed to pay $298 in taxes plus the rest in interest and penalties, and she cleared up the debt within a few months.