The FBI was asked yesterday to investigate the mysterious delivery of a package containing a videotape and a half-inch stack of documents relating to Texas Gov. George W. Bush's preparation for this fall's presidential debates to a close friend of and adviser to Vice President Gore.

The bizarre episode came a day before representatives of the Bush and Gore campaigns are scheduled to meet with the Commission on Presidential Debates to begin negotiations for the forums between the candidates.

The package, carrying a postmark of Austin, Tex., arrived at 10:28 a.m. at the lobbying firm of former House member Tom Downey, who had been tapped by Gore to play the role of Bush in the vice president's debate training sessions. After briefly viewing the videotape and scanning the documents, Downey called his lawyer, Marc Miller, and asked him to turn them over to the FBI. The FBI took possession of the package yesterday afternoon.

Downey, who has helped Gore with previous debates, said it was quickly clear to him that he was dealing with internal Bush campaign information. "I know what debate books look like," he said. "I knew from looking at it that this was stuff I should not see. This was their most sensitive stuff."

Downey said the videotape showed Bush and Sen. Judd Gregg (R-N.H.), who is playing Gore in Bush's debate preparation, along with a moderator whom Downey did not recognize. Downey said the documents had cover sheets indicating that they were proposed Bush responses to possible questions from Gore. "I watched it for 30 to 60 seconds," Downey said of the videotape. "I shut it off and said I shouldn't be looking at this."

Downey informed Gore campaign officials of his decision to give the material to his lawyer, and Gore chairman William Daley called Bush chairman Don Evans to inform him of what had happened.

Bush campaign officials reacted cautiously to the news. "We do not know what the Gore campaign claims to have in their possession," said spokesman Ari Fleischer. "We take this very seriously and our attorneys are looking into it so we can determine exactly what is on the tape they claim to have."

Fleischer said that until the Bush campaign learns more about what was in the package, "we're not going to jump to any conclusions or make accusations about it or anybody, including the Gore campaign."

Gore spokesman Mark Fabiani said the vice president was informed of the events and approved of Downey's handling of it. "I can tell you the Gore campaign wants nothing to do with any information regarding Bush's debate preparation," Fabiani said.

FBI spokesman John Collingwood, in a statement, said the bureau was "assessing the matter to determine which, if any, federal statutes are applicable."

Downey said the package included a cover letter from an "Amy Smith," which he and his associates concluded was a pseudonym. "The cover letter said: Here's these materials, I'll be back in touch if you need more," Downey said, making clear he was paraphrasing the letter.

The package arrived as Downey was in the midst of a session with three associates to help prepare himself to play Bush in practice debates. The three joined Downey to view the opening seconds of the tape.

After turning the materials over to his lawyer, Downey decided to take no further role in Gore's debate preparation, as a sign of good faith to the Bush campaign. "Al's going to do well in this debate," he said. "There's no reason to sully it by someone sending me something I shouldn't have."

Bush has been preparing for the debates for many weeks, and most of his practice sessions have been videotaped. If the material delivered to Downey proves genuine, the leak would represent a serious security breach inside Bush's campaign.

In 1980, advisers to candidate Ronald Reagan received briefing papers from President Jimmy Carter's campaign and used them in debate preparation. The Justice Department found no evidence of a crime.

Neither the Bush nor the Gore campaign expressed concern that the episode would cloud the opening round of debate negotiations today. Gore will be represented by Daley, Labor Secretary Alexis Herman and former Fannie Mae chairman James Johnson. Bush's team includes Evans, campaign manager Joe Allbaugh and former transportation secretary Andrew Card.

Earlier, Bush had rejected the commission schedule of three presidential debates and one vice presidential debate, seeking to participate in just one of the commission debates while agreeing to two other forums hosted by individual television networks. Gore has said he will consider other forums once Bush agrees to the commission schedule.