Many of the abuses the report describes have previously been disclosed, but it was not known that F.B.I. agents had gone so far as to document accusations of abuse in a “war crimes file” at Guantánamo. The report does not say how many incidents were included in the file after it was started in 2002, but the “war crimes” label showed just how seriously F.B.I. agents took the accusations. Sometime in 2003, however, an F.B.I. official ordered the file closed because “investigating detainee allegations of abuse was not the F.B.I.’s mission,” the report said.

The inspector general, Glenn A. Fine, found that in a few instances, F.B.I. agents participated in interrogations using pressure tactics that would not have been permitted inside the United States. But the “vast majority” of agents followed F.B.I. legal guidelines and “separated themselves” from harsh treatment, the report says.

The report says that the F.B.I. “had not provided sufficient guidance to its agents on how to respond when confronted with military interrogators” who used interrogation techniques that were not permitted by the F.B.I., and that fueled confusion and dissension. But it also says that “the F.B.I. should be credited for its conduct and professionalism in detainee interrogations in the military zones.”

Jameel Jaffer, who tracks detainee issues for the American Civil Liberties Union, took a more critical stance, saying the report shows “the F.B.I.’s leadership failed to act aggressively to end the abuse.” Mr. Jaffer said the report “only underscores the pressing need for an independent and comprehensive investigation of prisoner abuse.”

The report documents in greater detail than ever before the conflict between the F.B.I. and the C.I.A. over interrogation methods, which began with the capture of Abu Zubaydah, a senior Qaeda figure, in Pakistan in March 2002. F.B.I. agents began the interrogation using traditional rapport-building methods, and one agent even provided personal care for Mr. Zubaydah, who had been shot three times and grievously wounded, “even to the point of cleaning him up after bowel movements.”

But C.I.A. personnel who took over the case within a few days began to use harsher methods that one F.B.I. agent described as “borderline torture,” and which the C.I.A. has acknowledged included waterboarding, in which water is poured over the prisoner’s mouth and nose to create a feeling of suffocation.

The report describes extensive debate inside the F.B.I. over the next six months over whether it should continue to observe or assist the C.I.A. with interrogations using harsh methods it believed were counterproductive.