WASHINGTON, Sept. 26 - The Justice Department's inspector general and the F.B.I. are looking into the demotion of a veteran federal prosecutor whose reassignment nearly three years ago shut down a criminal investigation of the Washington lobbyist Jack Abramoff, current and former department officials report.

They said investigators had questioned whether the demotion of the prosecutor, Frederick A. Black, in November 2002 was related to his alert to Justice Department officials days earlier that he was investigating Mr. Abramoff. The lobbyist is a major Republican Party fund-raiser and a close friend of several Congressional leaders.

Colleagues said the demotion of Mr. Black, the acting United States attorney in Guam, and a subsequent order barring him from pursuing public corruption cases brought an end to his inquiry into Mr. Abramoff's lobbying work for some Guam judges.

Colleagues of Mr. Black, who had run the federal prosecutor's office in Guam for 12 years, spoke on condition of anonymity because of Justice Department rules that bar employees from talking to reporters. They said F.B.I. agents questioned several people in Guam and Washington this summer about whether Mr. Abramoff or his friends in the Bush administration had pushed for Mr. Black's removal. Mr. Abramoff's internal e-mail messages show that he boasted to clients about what he described as his close ties to John Ashcroft, then the attorney general, and others at the department.

Mr. Black's colleagues said that similar questions had been raised by investigators for the Justice Department's inspector general's office, which serves as the department's internal watchdog.

Spokesmen for the department in Washington have said there was nothing unusual about the timing of Mr. Black's reassignment in 2002. They said it was appropriate for the Bush administration to want to replace him with a permanent, Senate-confirmed United States attorney.

Mr. Abramoff, once one of the capital's best-paid lobbyists, is now the subject of a broad corruption investigation by federal prosecutors in Washington focusing on accusations that he defrauded Indian tribes and their gambling operations out of millions of dollars in lobbying fees.

A spokesman for Mr. Abramoff said he had "no recollection of being investigated in Guam in 2002" but would have cooperated if he had been aware of any inquiry at the time. Mr. Abramoff had a lucrative lobbying practice on Guam and the neighboring Northern Mariana Islands, another American territory; his lobbying clients paid for luxurious trips to the islands for several members of Congress.

Justice Department officials said they knew of no evidence to suggest that Mr. Ashcroft was involved in the decision to reassign Mr. Black. A spokesman for Mr. Ashcroft said the former attorney general and his aides at the Justice Department had done nothing to assist Mr. Abramoff and his clients and had had no significant contact with him.

Reached in Guam, Mr. Black, who continues to work as an assistant United States attorney, declined to answer questions about his 2002 reassignment.

The Los Angeles Times and news organizations in Guam have reported on questions about the circumstances of Mr. Black's demotion. The recent inquiries by the F.B.I. and by the Justice Department's inspector general had not been previously reported; nor had Mr. Black's contacts in November 2002 with the department's public integrity section about his investigation of Mr. Abramoff.

In a statement on Monday, the department said it was natural for the Bush administration to replace Mr. Black, whose assignment to run the United States attorney's office was never meant to be permanent, with a White House selection.

The department said the vetting process for Mr. Black's replacement, Leonardo Rapadas, the current United States attorney, was "well under way in November 2002," when the nomination was announced.

Colleagues said they recalled that Mr. Black was distressed when he was notified by the department in November 2002 that he was being replaced.

The announcement came only days after Mr. Black had notified the department's public integrity division in Washington, by telephone and e-mail communication, that he had opened a criminal investigation into Mr. Abramoff's lobbying activities for the Guam judges, the colleague said. The judges had sought Mr. Abramoff's help in blocking a bill in Congress to restructure the island's courts.

The colleagues said that Mr. Black was also surprised when his newly arrived bosses in Guam blocked him from involvement in public corruption cases in 2003. Justice Department officials said Mr. Black was asked instead to focus on terrorism investigations, which had taken on new emphasis after the Sept. 11 attacks.

"Whatever the motivation in replacing Fred, his demotion meant that the investigation of Abramoff died," said a former colleague in Guam.

The Justice Department's public integrity section is responsible for cases involving government corruption. It is now overseeing the larger investigation of Mr. Abramoff in Washington.

Representative George Miller, a California Democrat who has long focused on issues involving American territories in the Pacific, said the disclosures about Mr. Black's demotion raised questions about a possible conflict of interest at the Justice Department in its investigation of Mr. Abramoff.

"What this starts to suggest is that Abramoff's ability to corrupt the system was far more pervasive, certainly than we knew at the time," Mr. Miller said.

Commentary:

Other recent demotions:

Army Contract Official Critical of Halliburton Pact Is Demoted
Bunnatine H. Greenhouse

Lawrence A. Greenfeld: Demoted for doing his job
Lawrence A. Greenfeld

Anyone who supports Bush's nominees for the Supreme Court accepts the basic principle that he can break the law with impunity. IMO, every member of congress who votes for Roberts is an enemy of the United States. One way to stop illegal actions of a president is to strip him of power - including defeating his nominees who refuse to answer basic questions.