WASHINGTON (Sept. 10) - A lab document that the Justice Department failed to give Congress discloses that the FBI knew within eight months of the fiery end of the Branch Davidian siege that military tear gas projectiles were used, The Associated Press has learned.

A key final page from a 49-page FBI lab report was turned over to the House Government Reform Committee this week, along with an internal Justice Department memo acknowledging it ''was not produced to Congress'' during the 1995 investigations into the tragedy near Waco, Texas.

The first 48 pages of the lab report, dated Dec. 6, 1993, had been turned over to lawmakers years ago, absent the mention of the military-style tear gas that government officials for years had denied using.

The 49th page, obtained Friday by AP, discloses that FBI investigators who examined the scene at Waco found a ''fired US military 40 mm shell casing which originally contained a CS gas round,'' and two ''expended 40mm tear gas projectiles.''

The report is likely to become a key piece of evidence in the independent inquiry ordered by Attorney General Janet Reno and separate congressional investigations into whether government officials tried to cover up the use of potentially incendiary tear gas on the final day of the siege.

Justice Department and FBI officials denied for years that such tear gas grenades were used on April 19, 1993, the day the Davidian compound went up in flames. They abruptly reversed course earlier this month and acknowledged a ''very limited number'' of such devices were fired hours before the fatal fire.

The government continues to maintain that religious sect members set the fire, and federal agents did not contribute to it. They have said the tear gas canisters bounced off a roof of a concrete bunker and into a field. Sect leader David Koresh and some 80 followers perished during a later blaze in a wooden structure away from the bunker.

Justice spokesman Myron Marlin said Friday night that former Republican Sen. John Danforth, who is heading an independent inquiry into Waco, will have to examine why the crucial page of the report did not reach Congress earlier. Marlin noted, however, that the page was properly turned over to lawyers in criminal and civil cases involving Waco survivors.

''Whether it was an adminstrative error is something that the special counsel will have to look at,'' he said. ''But we know that the plaintiff and defendants counsel received it.''

The lab report does not specifically state whether the gas in the shells was incendiary or when they had been fired. But the potentially flammable M651 tear gas canisters that the FBI belatedly acknowledged using on the final day of the siege are 40mm military shells like those described in the lab report.

The FBI has always acknowledged firing one other type of 40 mm round that contained nonflammable tear gas.

A Sept. 2, 1999 Justice Department memo on the history of the lab document notes that the department's document database ''contains multiple copies of this document, most of which contain all 49 pages.'' It said only four copies of the report were missing the last page.

''It appears that the page on which mention is made of a shell casing for a military CS round and the expended tear gas projectiles was not produced to Congress,'' trial attorney James G. Touhey Jr. wrote.

During congressional probes, the FBI would typically forward its documents to the Justice Department, which would then produce the documents to lawmakers.

Danforth, a former Missouri attorney general, was named Thursday to oversee the independent inquiry. He promised to investigate whether government officials were responsible for the fatal fire and tried to cover it up.

Also Friday, congressional aides sifted through documents subpoenaed from the Texas Rangers dealing with the fiery end of the 51-day siege. The documents were subpoenaed last week by the House Government Reform Committee and included a previously unreleased Rangers report on ordnance used by the FBI in the final hours of the siege, a congressional aide said.

Texas Department of Public Safety spokesman Tom Vinger, whose agency oversees the Rangers, said the report represents ''an extremely exhaustive look at some of the controversial evidence.''

''When you get right down to it, it is very narrow in focus,'' Vinger said. He declined to be more specific.

The Rangers, who have stored tons of evidence collected from the Davidians' charred compound, began re-examining their holdings in June after learning that military pyrotechnic tear gas canisters were fired in the siege's waning hours.