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“Why did you mislead me and my colleagues?” Mr. Hatch said.

Acting IRS Commissioner Steven Miller, who has been forced to resign, said he never lied to the Senate.

But Mr. Miller did apologize more than once, adding onto his tour of contrition on Capitol Hill after an appearance on Friday before the House Committee on Ways and Means.

Yet he reiterated his belief that officials in the Cincinnati suffered from a lack of guidance and oversight — not political animus against conservatives.

Sen. Mike Crapo, Idaho Republican, said he does not buy that explanation.

“I think it is almost beyond belief,” he said, that officials had nonpartisan reasons for scrutinizing conservative organizations.

He noted the inspector general had to rely on the word of people implicated in the scandal, and they weren’t under oath when they provided information for the audit.

The turmoil surrounding the IRS broke on Friday, when Lois Lerner, director of exempt organizations for the Internal Revenue Service, apologized for the extra scrutiny during an event with the American Bar Association.

Mr. Miller said the question-and-answer that led to the apology was arranged ahead of time and was intended to get out in front of the story, since the inspector general had finished his report.

Mr. Obama’s spokesman, Jay Carney, said Monday that White House counsel Kathryn Ruemmler learned of audit last month, but had limited detail and kept Mr. Obama out of the loop to insulate him from the investigation.

According to the inspector general’s report: In early 2010, specialists in the Cincinnati field office began to search for applications with terms such as “tea party” or “patriot” in their names. By July of that year, the unit’s manager asked the specialists to “be on the lookout” for tea party cases.

Ms. Lerner ordered the Cincinnati field office in July 2011 to change its criteria to “political, lobbying or advocacy” when deciding which 501(c)(4) applications to flag.

But specialists, viewing her instructions as too broad, again started to use policy-based criteria in January 2012.

Republican lawmakers raised questions about reports of intense and laborious scrutiny of conservative groups seeking tax-exempt status, which prompted the audit. The IRS changed its criteria once more in May 2012 to bring it in line with Treasury Department regulations.

The inspector general concluded the specialists were not motivated by politics, but used inappropriate criteria because of lax oversight.