A Northwest Washington woman has sued the superintendent of St. Elizabeths mental hospital, D.C. Police Chief Maurice Turner and FBI Director William Webster for $20 million, claiming that their negligence resulted in the death of her son.

According to a suit filed Monday in D.C. Superior Court, Alexander Ghebhardt died of exposure and lack of medication on Sept. 14, 1984, six days after he walked off the grounds of St. Elizabeths and went to Maryland.

He had been committed to St. Elizabeths in April 1983 by D.C. Superior Court Judge Richard S. Salzman for being "likely to injure himself and others if allowed to remain at liberty," according to the suit filed by Ghebhardt's mother, Alexandrina Svoronou.

He needed frequent medication for physical and mental disorders, and was in "life-threatening danger" if denied the medication for hours or days, it said.

The suit charges that St. Elizabeths was negligent in allowing Ghebhardt the freedom of the hospital grounds and failing to include information in its missing persons report about Ghebhardt's need for medication that would have upgraded the urgency of his disappearance.

It also charges that the police department and the FBI were negligent in not communicating the urgency of the need to find Ghebhardt.

Spokesmen for St. Elizabeths, the police department and the FBI all declined comment, saying that it would be inappropriate to discuss a pending lawsuit.

The suit contends that, as a result of the alleged negligence, Ghebhardt suffered humiliation by authorities on the Metroliner and in the custody of the Baltimore City police, as well as deprivation of food and drink while in the open countryside night and day, and physical and emotional suffering before his death.