A Montgomery County judge reluctantly granted Edward Thomas Mann permission yesterday to be his own lawyer at his trial on charges of murdering three persons and attempting to murder 23 others at the IBM office building in Bethesda last May.

Circuit Court Judge John J. Miller told Mann -- who could be sentenced to death if convicted -- he was making a "bad mistake" by dismissing widely known defense attorney R. Kenneth Mundy and Mundy's associate Joseph Miller, who were to have represented him. Mann's trial, scheduled to begin Dec. 6, is expected to last at least a month.

The judge questioned Mann at length about his education and understanding of the problems in representing himself, trying repeatedly to convince Mann that he should not be without professional assistance.

At one point Miller warned that "these lawyers [Mundy and Gibson] will put up a much better defense than you, and I think you know that."

"That has nothing to do with my rights," Mann responded bluntly.

When Miller asked why Mann feels qualified to represent himself, Mann said that although he has no legal experience he has a strong belief in himself.

He said that when he went to Clifton T. Perkins state mental hospital for pretrial examination, "they brought out that my IQ is 122. My past experience has taught me that I would do better if I represent myself."

Mann, 38, of Mitchellville, who was once employed by IBM, drove his Lincoln Continental through the glass doors of the company's building off Democracy Boulevard near Montgomery Mall on May 28, then went on a 7 1/2-hour shooting spree, according to police accounts.

He has pleaded not guilty by reason of insanity.

Doctors at Perkins concluded that he is competent to stand trial. Assistant Montgomery County prosecutors Michael Mason and Roger Galvin, supporting Mann's request to represent himself, called psychiatrist Michael Spodak to the witness stand yesterday to testify that the defendant is still mentally competent to do so.

Judge Miller granted a request by Galvin that a "standby attorney" be appointed to be called if Mann exhibits "outrageous conduct" during his trial.

Mann said his major dispute with Mundy revolved around Mundy's refusal to file a motion that Mann be released on bond and Mundy's efforts to prevent him from holding interviews with the news media.

"I might agree with your attorneys that filing for a bond might be a futile act," Judge Miller said. "Although you have a right to bail, such a right has usually not been applied to capital cases."

As for statements to the media, Miller warned Mann that any statement he made to anyone might be used against him by the government at trial.

"The members of the media are not the ones who will determine your guilt or innocence," the judge said. "It will be a jury of 12, and that's where your attention should be."

The judge said Mann had asked that his wife, Rosa, be allowed to assist in his defense.

Although his wife could help him with legal research in the case, Miller said, she may not speak for him in the courtroom because she is not an attorney.

Rosa Mann said after the hearing she would have no comment on her husband's decision.

Mann told the judge he wants to be released on bond because the law library at the Montgomery County Detention Center is inadequate and he wants to be free to research his case at other libraries throughout the area.

After the hearing, Mann, wearing dark green prison clothes, held whispered conversations with both his wife and Mundy, then showed little emotion as he was handcuffed by sheriff's deputies and led from the courtroom.

Outside the courthouse, Mundy, who had requested to be released from the case, said that with proper legal representation, he believes Mann "would have an excellent chance" of being found innocent.

He said not aware of any precedent in which a person who has pleaded innocent by reason of insanity to a major criminal offense has successfully represented himself.

In addition to three murder charges and 23 of attempted murder, Mann faces 23 charges of assault with intent to murder and 26 of using a handgun in a violent crime.