Without yet putting on a witness, D.C. Mayor Marion Barry's legal team revealed three significant features yesterday of the mayor's forthcoming defense on drug and perjury charges.

The first, a surprise, was a last-minute request to introduce expert testimony on the effects of crack cocaine on human memory. Defense lawyer R. Kenneth Mundy said the evidence would be relevant to the "accuracy . . . of the government's witnesses."

Some legal strategists saw another, unspoken aim: To suggest a defense against felony charges that the mayor lied "knowingly" to a grand jury about drugs.

The second defense tactic, anticipated by outside strategists, carried subtantially higher risks. After extraordinary efforts by Mundy failed to force prosecutors to put a senior FBI agent on the witness stand, co-counsel Robert W. Mance said that Mundy would call the agent himself as a hostile witness. Mundy plans to use the agent, Ronald Stern, as a foil for defense claims that the government had a vendetta against the mayor.

The third defense disclosure was that James Stays, a member of Barry's security detail, will be the first witness for the mayor.

Prosecutors have gone out of their way throughout the trial to elicit evidence that Stays and other security officers turned a blind eye to drug use by the mayor. The defense will have another view: that three sworn police officers saw no drugs because there were none.

Mundy disclosed nothing yesterday on the most significant decision for Barry: whether he would testify. That, he told U.S. District Judge Thomas Penfield Jackson, is an ongoing question.

Mundy told the judge he had two local experts lined up to describe the impact of long-term cocaine use on "the mind or the power to recall." He did not identify the experts.

It is not uncommon in District courts for the defense to use the cocaine habits of government witnesses to cast doubt on their capacity to observe and recall events. Mundy and Mance both asked questions along those lines in the 20 days of government testimony.

But legal and medical authorities said yesterday that there is additional evidence available from an expert witness, and it centers on a phenomenon known as "confabulation."

Observed among alcoholics since early in the century, the phenomenon apparently was first described in long-term, high-dose cocaine users by Harvard neuropsychiatrist Milton E. Burglass.

Confabulation, Burglass said in a 1985 article, "refers to the unconscious filling in of memory gaps by imagined experiences, fabricated stories, or grossly distorted accounts of recent or remote events."

Burglass said in a telephone interview yesterday that the phenomenon can account both for lapses in memory and invented memories.

"You make up stories," he said. "There's a period of time for which you have no recall or missing pieces, and in order to make ongoing logical sense out of your life's experience, the brain . . . creates stories . . . . It's entirely distinct from lying. People who are confabulating would pass a lie-detector test."

Henry W. Asbill, a defense lawyer who is following the Barry case, said evidence about cocaine confabulation might be tailor-made to clear Barry of perjury. The government must prove not only that Barry made false statements under oath, but that he did so knowingly, Asbill said, and confabulation offers a possible defense.

Assistant U.S. Attorney Judith E. Retchin perceived that potential immediately yesterday, reminding the judge that Mundy had explicitly promised not to use a "mental capacity" defense against the perjury charges. Mundy initially had given prosecutors the legally required notice that he would put on such a defense, but withdrew it when the government sought access to Barry's medical records.

The judge replied that Mundy was not talking about the effect of cocaine on Barry, but on government witnesses.

As for the FBI testimony, Stern is the most visible of the agents involved in the case. It was Stern, for example, who was shown escorting Barry into Barry's home after his release on the night of his arrest.

Although Jackson has limited what Mundy can develop from agents, including questions about the probe's cost and length, there are several ideas the defense would like to plant in jurors' minds.

For example, Mundy is likely to ask Stern why the FBI's public corruption specialists have spent the past 18 months pursuing a drug investigation of Barry. The clear implication for the jurors from such a line of questioning would be that the government had targeted Barry but was unable to bring a case against him based on government fraud, deciding instead to mount a drug investigation.

The danger for Mundy in pursuing such a strategy is that those questions would allow Stern to testify about how the FBI decided to conduct its investigation and could render admissible all of the previous leads that law enforcement agencies had amassed on Barry before the Ramada Inn episode of December 1988.

Before calling Stern, Mundy is expected to call D.C. police officers Stays and Warren Goodwine. Stays is the senior member of Barry's security detail.

Hazel Diane "Rasheeda" Moore testified that on one occasion Stays was assigned to baby-sit for her while she went out to buy drugs for herself and the mayor. Before she left her house, Moore testified, Stays suggested to her that he was aware of her involvement in drugs.

Stays is expected to deny any knowledge that Moore and Barry were involved in drugs.

Stays and Goodwine, who has been transferred to the department's recruitment office, accompanied Barry to the Virgin Islands in 1988, a trip on which Charles Lewis testified that he and Barry used drugs. Goodwine is expected to testify that he saw no drugs and that he, too, was not aware Barry was involved in drugs.