report issued yesterday by the House Committee on Government Reform gave the fullest accounting to date of the F.B.I.'s use of murderers as informants in Boston for three decades and its protection of them even to the point of allowing innocent men to be sentenced to death.

The Federal Bureau of Investigation's policy "must be considered one of the greatest failures in the history of federal law enforcement" and had "disastrous consequences," the report said.

More than 20 people were killed by F.B.I. informants in Boston starting in 1965, often with the help of F.B.I. agents, it said, but no F.B.I. agent or official has ever been disciplined.

Separately, it said William M. Bulger, then the president of the University of Massachusetts, gave "inconsistent" testimony to the committee last June about whether the F.B.I. had contacted him in its search for his fugitive gangster brother, James Bulger, who is on the bureau's most wanted list. James Bulger, known as Whitey, headed an underworld gang in Boston and was one of the F.B.I.'s star informants before he fled in 1995 after being tipped off by a bureau agent to a secret indictment against him.

In his testimony in Washington, Mr. Bulger said the F.B.I. never asked him about his brother's whereabouts, though a retired agent later said he tried to speak to Mr. Bulger but was told that Mr. Bulger would not talk.

While critical of Mr. Bulger, the report stopped short of saying he had committed perjury.

And it said it there was insufficient evidence to find that Mr. Bulger, during his days as president of the Massachusetts Senate, used his influence to punish those who investigated his brother.

Mr. Bulger's lawyer, Thomas R. Kiley, said the committee's findings were "a total vindication on everything that matters" for Mr. Bulger.

The bureau, in a written statement, said, "While the F.B.I. recognizes there have been instances of misconduct by a few F.B.I. employees, it also recognizes the importance of human source information in terrorism, criminal and counter-intelligence investigations."

To avoid future problems, the statement said, "the F.B.I. has taken significant steps in recent years regarding the management and oversight of human sources of intelligence."

The F.B.I.'s policy of using murderers grew out of a belated effort by Director J. Edgar Hoover to go after the Mafia, which Mr. Hoover had earlier denied even existed, the report said. So in the early 1960's the bureau began recruiting underworld informers in its new campaign.

The report focuses heavily on one episode, the 1965 murder of Edward Deegan, a small-time hoodlum, who was killed by Jimmy Flemmi and Joseph Barboza, who had just been recruited by an F.B.I. agent in Boston, H. Paul Rico.

The F.B.I. knew the two men were the killers because it had been using an unauthorized wiretap at the headquarters of the New England Mafia in Providence, R.I., and had heard Mr. Flemmi ask the Mafia boss, Raymond Patriarca, for permission to kill Mr. Deegan. A few days later Mr. Deegan was shot to death.

The F.B.I. was so intent on protecting its new informants, the report said, that it passed up a chance to try Mr. Patriarca for his involvement in the killing. Instead, four men who had nothing to do with the killing were tried and convicted, with two sentenced to death and two to life in prison. Two of the men later died in prison, and two had their sentences commuted and were freed after serving 30 years behind bars.

Mr. Hoover was kept fully informed about this murder and the wrongful convictions, the report said.