WASHINGTON — FBI investigators do not believe Internal Revenue Service officials committed crimes in the unusually heavy scrutiny of conservative groups that applied for tax-exempt status, a law-enforcement official said Monday.

Prosecutors for the Justice Department who have been overseeing the case have not decided whether to file charges against the officials — although that would seem unlikely given the investigators’ conclusion, according to the official.

Despite an admission by the IRS that it inappropriately targeted conservative organizations, by searching for groups with the words “Tea Party” or “Patriots” in their names, many legal experts and law-enforcement officials say they do not believe the scrutiny broke the law.

Some members of Congress had called for the Justice Department to investigate the tax-collecting agency.

IRS documents show the agency gave the same scrutiny to some liberal groups, using the key words “Progressive” and “Occupy.”

The news that criminal charges are unlikely is not expected to stop the debate over whether politics had motivated the IRS scrutiny.

Last week, two senior House Republicans sent a letter to the Justice Department demanding that the prosecutor overseeing the case be removed because she had donated money to President Obama’s election campaign.

The letter sent by Rep. Darrell Issa of California, the chairman of the House Committee on Oversight and Government Reform, and Rep. Jim Jordan of Ohio, the head of the Regulatory Affairs subcommittee said prosecutor Barbara Bosserman had donated at least $6,750 to Obama and the Democratic National Committee.