The Justice Department will investigate complaints that federal authorities acted improperly in planning a sting intended to catch then-D.C. Mayor Marion Barry accepting cash in return for providing a city job, Deputy Attorney General Eric H. Holder Jr. said yesterday.

"We have referred that matter to our Office of Professional Responsibility," Holder said at a Justice Department briefing.

The Office of Professional Responsibility investigates allegations of criminal or ethical misconduct by Justice Department employees. The office can impose administrative penalties and recommend criminal prosecutions. The investigations typically entail months of legwork, including interviews with virtually anyone who might have knowledge about a case.

Barry demanded an investigation after news about the proposed FBI sting surfaced two weeks ago. He alleged that FBI agents and federal prosecutors had no reason to believe he would sell a D.C. government job. His attorney, Frederick D. Cooke Jr., followed up with a formal letter to Attorney General Janet Reno that said the tactics were entrapment.

"These agents . . . had no evidence that Mr. Barry was predisposed to commit the criminal offense involved in the 'sting,' " Cooke wrote Reno.

Holder, who headed the U.S. attorney's office in the District from 1993 until 1997, said that he has not been given details about the matter but that the nature of Barry's allegations calls for a thorough investigation.

The sting plans were developed early last year, after the arrest of then-D.C. police Lt. Yong H. Ahn on corruption charges. Hoping to receive a lighter sentence, Ahn secretly pleaded guilty in U.S. District Court and began cooperating with authorities in various investigations. According to Ahn and others, the FBI was most keenly interested in pursuing Barry.

The FBI's plan called for Ahn's wife, Azita Ahn, to meet with Barry at an acquaintance's home in Northern Virginia and give Barry $5,000 in return for a job. The meeting never took place. U.S. Attorney Wilma A. Lewis, Holder's successor, refused to authorize the operation, and the news media learned about Ahn's arrest, ending his undercover work.

Law enforcement sources said prosecutors believed that the FBI lacked a foundation for moving ahead with a sting.

Details about the proposed sting were included in court documents and transcripts recently unsealed in Ahn's case. Ahn was given a four-month prison sentence last month, getting credit for helping investigators.

Barry, who did not seek reelection last year, was the target of numerous federal investigations during his four terms as mayor. He was convicted once, of a misdemeanor drug charge, after his arrest in a 1990 sting at the Vista Hotel. He has contended that the FBI had a vendetta against him.

The Office of Professional Responsibility is headed by H. Marshall Jarrett, a career prosecutor who supervised Barry's drug prosecution while he was working in the U.S. attorney's office. Although Jarrett played no role in last year's sting plans, he has recused himself from taking part in the internal probe because of his previous work, officials said yesterday.