WASHINGTON — The ousted head of the Internal Revenue Service apologized this morning to Congress for his agency’s tougher treatment of tea party and other conservative groups seeking tax-exempt status.

He said they resulted from a misguided effort to handle a flood of applications, not political bias.

“I want to apologize on behalf of the Internal Revenue Service for the mistakes that we made and the poor service we provided,” Steven Miller, who has been acting IRS commissioner, told the House Ways and Means Committee as the panel held Congress’ first hearing on the episode.

“The affected organizations and the American public deserve better. Partisanship and even the perception of partisanship have no place at the Internal Revenue Service.”

At a hearing that saw lawmakers from both parties harshly criticize his agency, Miller conceded that “foolish mistakes were made” by IRS officials trying to handle a flood of groups seeking tax-exempt status. He said the process that resulted in conservatives being targeted, “while intolerable, was a mistake and not an act of partisanship.”

Though Miller and another top IRS official are stepping down, the chairman of the committee said that would not be enough.

“The reality is this is not a personnel problem. This is a problem of the IRS being too large, too powerful, too intrusive and too abusive of honest, hardworking taxpayers,” said Rep. Dave Camp, R-Mich.

Camp also said the tougher examinations that conservative groups encountered seemed to be part of a “culture of cover-ups and intimidation in this administration.” He offered no other examples.

Miller said the IRS struggled to efficiently handle growing numbers of applications for tax-exempt status.

The agency has said between 2008 and 2012, the number of groups applying for tax-exempt status as so-called social welfare groups more than doubled. Along with that was an increase in complaints that such groups were largely engaging in electoral politics, which is not supposed to be their primary activity.

“I do not believe partisanship motivated the people” at the IRS who engaged in the harsher screening for conservative groups, Miller said.