ASHINGTON, Aug. 27 — A new Senate report on intelligence failures before Sept. 11 has concluded that ignorance and ineptitude of F.B.I. supervisors and lawyers in Washington blocked field agents around the country from pursuing evidence that might have helped provide the bureau with what one of the authors of the report called a "veritable blueprint for 9/11."
The report by the Senate Judiciary Committee, which is expected to be made public next month and is the result of an investigation that began shortly after the terrorist attacks, focuses on the mishandling of the case against Zacarias Moussaoui, the only person charged with involvement in the Sept. 11 attacks.
The report suggests that while the Moussaoui case was particularly egregious, it may be indicative of the bureau's bungling of other sensitive counterterrorism cases before Sept. 11. A draft copy of the report was provided today to The New York Times by Congressional officials on condition that they not be identified.
In the Moussaoui case, the report found, F.B.I. counterterrorism specialists and the bureau's lawyers were so ignorant of federal surveillance laws that they did not understand that they had ample evidence to press for a warrant to search the belongings of Mr. Moussaoui, a French national who was arrested weeks before the attacks after arousing the suspicion of instructors at a Minnesota flight school.
Instead, the report found, the F.B.I. supervisors and lawyers aggressively blocked the search warrant sought by desperate field agents in Minnesota who believed last August that they might have a terrorist on their hands who might use a commercial airplane as a weapon.
The Minnesota agents had sought the warrant under the 1978 Foreign Intelligence Surveillance Act, or FISA, which sets a relatively low standard for the evidence required for searches of suspected spies or terrorists; standard criminal warrants require a much higher standard of evidence.
Officials said a search of Mr. Moussaoui's computer and other belongings after Sept. 11 turned up information on commercial airplanes, crop-dusting and a telephone number in Germany for a suspected member of the Qaeda terrorist network.
That evidence, coupled with other information in the hands of the same F.B.I. counterterrorism supervisors last summer, would have provided a "veritable blueprint for 9/11," said Senator Arlen Specter, Republican of Pennsylvania, who is a member of the Judiciary Committee and an author of the report.
The other information, Mr. Specter said, included a report sent to Washington by a field agent in Phoenix who had warned of a threat posed by an unusual number of young Arab men seeking flight training in the United States, as well as intelligence reports about terrorist meetings in Malaysia that involved some of the Sept. 11 hijackers.
He said the decision by F.B.I. supervisors in Washington to rebuff the Minneapolis agents, and the supervisors' ignorance of the standards of evidence required for a search warrant, were "inexplicable."
F.B.I. spokesmen said the bureau had not seen the Senate report and would have no immediate comment on it. But other law enforcement officials said the F.B.I. supervisors singled out for blame in the report believed that they acted properly last summer and had tried to work with the Minneapolis agents to secure enough evidence to seek a warrant to search Mr. Moussaoui's belongings before Sept. 11.
"Factually, they couldn't link him to a recognized terrorist group, or to any terrorist group," a senior law enforcement official said. "They felt they didn't have the evidence."
The essential elements of the Moussaoui debacle have been known since last spring, when an F.B.I. whistleblower from the bureau's Minneapolis office came forward to complain that Washington supervisors had mishandled the case, and that they might be trying to cover up their mistakes.
The Judiciary Committee's draft report found F.B.I. supervisors in Washington had set "too high a standard" for evidence for counterintelligence search warrants in Mr. Moussaoui's case and others.
The bureau officials, the report said, "impose a higher standard on themselves than that required by the Constitution before seeking to obtain a warrant," with the result that important searches of terrorism suspects are not carried out.
In Mr. Moussaoui's case, the report said, bureau supervisors rejected the search warrant request "despite their strong suspicions with respect to Moussaoui." It added, "Without going into the actual evidence in the Moussaoui case, there was ample evidence to confirm these suspicions."
The Senate report, which is likely to bring further pressure on the F.B.I. director, Robert S. Mueller III, to shake up the bureau's counterterrorism unit and replace or discipline supervisors, does not identify by name the supervisors and lawyers who may have mishandled the Moussaoui case. But some are identified by their title, including supervisors in the bureau's Radical Fundamentalist Unit.
Senate officials involved in the preparation of the Judiciary Committee report said they were eager for its findings to become public in light of last week's disclosure that the nation's secret intelligence court had harshly criticized the F.B.I.'s performance under FISA, and that the court had accused the Justice Department of overreaching in its recent request for broad new powers under the surveillance law.
The court, the Foreign Intelligence Surveillance Court, which was established under the 1978 law, weighs F.B.I. applications for wiretaps and other searches of people suspected of espionage or of terrorism. In an unclassified ruling that it provided last week to the Judiciary Committee, and that the panel subsequently released, the court identified more than 75 cases during the Clinton administration in which the bureau had provided misleading applications.
The ruling also rejected a Bush administration request to tear down the "wall" that for years has prevented criminal investigators from being actively involved in counterintelligence wiretaps. The administration had cited the new authority it received under a sweeping counterterrorism law passed after Sept. 11.
The institutional wall was erected in the 1978 law to prevent prosecutors from using the lower evidentiary standards of the FISA act to eavesdrop on criminal suspects, possibly as an end-run around the Constitution's prohibition on unreasonable searches.
Mr. Specter said the department appeared to have misread the intent of Congress when it passed the antiterrorism bill. He suggested that the F.B.I. and the Justice Department already had ample investigative power under the surveillance law, and that they had failed to use it properly.