FBI Director Louis J. Freeh has told Attorney General Janet Reno that a new investigation of the fiery end to the 51-day siege of the Branch Davidian compound near Waco, Tex., should be conducted by outside investigators and not his agency, FBI officials said yesterday.

The FBI has designated 40 agents to conduct such an investigation and "everyone in the bureau feels that we are perfectly capable of doing a complete, impartial and thorough investigation," said Tron Brekke, an FBI spokesman.

"But the perception is that the FBI cannot investigate itself, that there is an inherent conflict of interest," Brekke added. Because of that, he said, Freeh has urged Reno to appoint an outsider to head a new Waco investigation and have the investigative work done without FBI involvement.

"Whatever this investigation turns up that can help us restore our credibility is welcomed," Brekke said.

A Justice Department official said last night that Reno has not decided how the investigation should be conducted or whether the FBI should play a role. But Freeh's public support for an outside investigation appeared in part a preemptive strike in anticipation of her decision. A law enforcement source said that Reno has not told Freeh how the investigation will be structured but that it is widely assumed in the bureau that it will done by outside investigators.

Reno vowed last week to launch a new investigation and to "get to the truth" about the final assault on the Branch Davidian compound after the disclosure that FBI agents fired at least two incendiary tear gas canisters on the morning of the assault. The FBI has insisted that the fire that engulfed the compound, where 76 people died, was set by Branch Davidian leader David Koresh and his followers, and for six years it denied using weapons that could have sparked a fire.

The agency still maintains that there is no evidence to suggest it had anything to do with the fire. The FBI said last week that the two incendiary tear gas devices were not fired at the wooden compound that burned but at a concrete bunker some distance from the compound and that they were set off several hours before the fire began.

Congressional committees are planning their own investigations into the latest revelation about the Waco incident. The House Government Reform Committee has issued subpoenas for documents that relate to the use of pyrotechnic tear gas canisters and was preparing new subpoenas yesterday.

Meanwhile, the Dallas Morning News reported yesterday that a federal prosecutor who has been deeply involved in the Waco case has told Reno that "individuals or components within the Department of Justice" may have withheld evidence from her. Bill Johnston, an assistant U.S. attorney in Waco, told the newspaper, "I'm very concerned that information which should have been made known to her and to the public has not been."

The Justice Department also filed a brief in federal court in Waco yesterday supporting a request by the Texas Department of Public Safety that it be allowed to turn over Waco-related material to the court. But the Justice Department objected to a court order that broadened this request to include all material "in any way relevant" to the Waco siege held by any agency, including federal agencies. It said the broadened court order imposes "an excessive and unwarranted burden on the government" as it prepares to defend against civil lawsuits that have been filed by relatives of Branch Davidians.

House Judiciary Committee Chairman Henry J. Hyde (R-Ill.), mindful that Waco hearings in 1995 degenerated into partisan bickering, is considering creating a House-Senate commission, the Associated Press reported.

A joint commission would have its own budget and investigative authority. Its members likely would be appointed by House and Senate leaders from both parties but would not necessarily be lawmakers, a Judiciary Committee spokesman said.

Staff writer Richard Leiby contributed to this report.