VIRGINIA BEACH, Va. - The job of keeping John Allen Muhammad alive, should he be convicted in last year's Washington-area sniper attacks, has become more difficult after his refusal to speak to the prosecution's psychiatrist, legal experts said yesterday.

Judge LeRoy F. Millette Jr. ruled late Monday that the only way Muhammad's attorneys could present expert testimony related to their client's mental health would be if he consented to a meeting with forensic psychiatrist Dr. Park Dietz, a favorite of prosecutors in high-profile cases. When Dietz visited Muhammad in his Manassas, Va., jail cell the week before his trial was to begin, the suspect turned the doctor away.

"That piece of evidence is absolutely crucial for possibly saving Mr. Muhammad from the death penalty," said Michael Greenberger, a law professor and director of the Center for Health and Homeland Security at the University of Maryland. "Are they going to get him off scot-free? No they're not. They're trying to save his life."

Should Muhammad be convicted, the trial would proceed to a penalty phase, where the jury would decide whether to sentence him to death. At that stage, Muhammad's attorneys are free to present what are called mitigating factors - those circumstances that jurors could count in his favor when weighing whether he should live or die.

Defense attorneys told the court Monday they had planned to introduce evidence regarding "abuse and neglect" in Muhammad's childhood that could lessen his "moral culpability" in the crimes. The attorneys did not outline any specifics.

Over the spring and summer, three mental health experts hired by the defense spent more than 60 hours interviewing Muhammad.

Dietz is a well-known California-based doctor who testified for the prosecution in the cases of Jeffrey Dahmer, John Hinckley Jr. and more. He has a reputation for being tough on defendants, several court watchers said.

Douglas L. Colbert, who teaches criminal law at the University of Maryland Law School, said he can understand any apprehension Muhammad may have in encountering Dietz.

"Any reasonable person would have reason to fear Mr. Dietz," he said. "He's as sure a bet to find someone sane and dangerous as an expert witness could be, based upon his past testimony."

But several legal experts following the trial say the judge's ruling to exclude the mental health experts, while fair under the circumstances, are much more detrimental to the defense than to the prosecution - no matter how damning Dietz's findings could be.

"As the defense you want the issue out there," said New York attorney Robert J. Cleary, a former prosecutor who handled the case of Theodore J. Kaczynski, known as the Unabomber.

Greenberger said he suspects that Muhammad's repudiation of Dietz - and a subsequent disagreement about it with his attorneys - could have been what led him to represent himself during the opening two days of the trial last week.

"His refusal to see the psychologist, I'm sure, has led to many, many unhappy discussions with him and his lawyers," he said. "He's tying their hands."

Muhammad's attorneys can still call relatives and friends to the stand to discuss the defendant's background and history. A mental health expert would be better able to connect the dots for the jury than a lay witness would be, legal experts said.

In court, Muhammad has been calm and controlled, a well-dressed man who confers with his attorneys, pays rapt attention to testimony and takes occasional notes.

"This is not a man who is so riddled by mental illness that he is not capable of speaking," said Steven D. Benjamin, a Richmond attorney who is president-elect of the Virginia Association of Criminal Defense Lawyers.

It will be harder for him to suddenly say to the jury, "Yeah, I'm suffering from some sort mental defect," Cleary said. "It's much more difficult for them to switch to accept suffering from some sort of psychological malady."

Leaving out the question of Muhammad's mental health could also have an effect on the community at-large, a public who spent weeks worrying whether it was safe to pump gas or let their children play outside. At the same time, some lawyers wonder if there is any evidence that could be presented to keep Muhammad from facing death.

"If they were to prove Muhammad is the cause of these 10 violent deaths with no purpose other than what was in Muhammad's mind ... how do you possibly mitigate that?" Benjamin asked. "Would any mental health testimony possibly mitigate 10 cold-blooded murders? I think we'll never know."