An Austrian doctor who bicycled each morning to the armed forces medical school in Bethesda has disappeared, and Montgomery County police said yesterday the only clue they have is his bicycle, which was found chained to a park fence miles from the doctor's normal route.

Police said that 35-year-old Rudolph W. Platzer, who had a one-year grant from the National Science Foundation of Switzerland and was studying the effect of poisonous and radioactive drugs on humans, has been missing since May 19.

According to accounts by his wife and a neighbor, Platzer set off that morning on a bicycle from his Maplewood Manor home a half-mile from the medical school on the grounds of Bethesda Naval Hospital. He was carrying a briefcase and wearing tan slacks and a green pullover, police said.

He pedaled a regular half-mile route each morning to get to the medical school, known formally as the Uniformed Services University of the Health Sciences, but that Thursday he never arrived, coworkers told police.

Platzer's bicycle was found five days later chained to a link fence close to a parking lot in Cabin John Regional Park, nearly four miles from his home and in the opposite direction from the hospital.

County police said no trace of Platzer or the briefcase was found during a search of the park by mounted police and dogs. Platzer's wife, a nurse, said he once visited the park but did not know the area, according to police.

Detective Steven Calarco, who is heading the investigation, said police have no explanation for Platzer's disappearance and are looking into the possibility that Platzer may have chosen to vanish.

Calarco said that the wavy-haired, bespectacled doctor was reported to have been depressed recently about his work and his lack of friends in this country and wanted to return to Switzerland.

Platzer's wife told police that her husband had not shown any signs of severe depression that might lead authorities to suspect suicide. The night before his disappearance, the couple had dinner with friends and he appeared to be in good spirits.

"It would be absolutely unlikely for him to leave like this ," Maria Platzer said yesterday. "I just cannot imagine how he could do something like that. He always says what he is going to do and where he is going." She said that relatives in Austria had not heard from him.

"He was simply a nice young physician, and we all liked him," said Lewis Aronow, hospital pharmacology department chairman. "It's true his studies were not going as well as he would have liked, but that is true of a lot of us here. His degree of unhappiness was relatively minor."

Calarco said that police are holding Platzer's passport and have notified the Austrian and Swiss embassies to watch for any requests for a duplicate passport. Calarco also said Platzer's local bank accounts are being watched, but that no large withdrawals had been made recently.

In addition to researching the effects of radioactive and poisonous drugs on the liver, Platzer was studying the use of computers in clinical medicine, a hospital official said.

Calaraco said nothing had been reported missing from the pharmacology department where Platzer was assigned.