During a week's leave from his job as a navigator at the Naval Research Laboratory in Washington last September, Lt. George M. Prior decided to polish his golf game at the Army Navy Country Club in Arlington a few miles from his home.

But before he played out his customary 36 holes, Prior, 30, complained to his partner that he had a headache, Prior's wife, Liza, said.

Later, the headache developed into what seemed like the flu and then a rash, she said. Four days after his golf game, Prior was in Bethesda Naval Hospital with a 104.5 degree fever and blisters all over his body.

Ten days later--after his kidneys, lungs, liver and heart failed--Prior was dead, his wife said.

This week, Liza Prior filed a $20 million lawsuit in Arlington County Circuit Court, contending that her husband's illness and death resulted from exposure to the fungicide Daconil, which is commonly used to prevent brown spots on lawns.

The lawsuit alleges that the country club was negligent in spraying the chemical on the golf course and that it failed to adequately warn patrons about alleged dangers of exposure to the substance.

It also alleges that the manufacturer, Diamond Shamrock Chemical Co., knew or should have known Daconil "posed a serious and potentially lethal health hazard" and that the company was "negligent and careless" in testing, designing, manufacturing, marketing and selling the chemical.

Ginger Shearburn, a spokeswoman for the chemical company, which is being sued for $16 million, declined to comment on the lawsuit. Robert Bennie, assistant general manager of the Army Navy Country Club, also declined comment, other than to say, "We've never had anything like this before."

Bennie said he did not know if the club, which is being sued for $4 million, is currently using Daconil on its lawns.

The official cause of Prior's death was pneumonia due to a toxic skin syndrome, a burning of the skin caused by exposure to a toxic substance, according to Dr. Jack Lord, a forensic pathologist at the Armed Forces Institute of Pathology at Walter Reed Army Hospital.

Lord, who did an autopsy on Prior, said in a telephone interview recently that through the use of special photographic equipment he has been able to detect the chemical on Prior's golf clubs, golf balls and shoes, as well as on the golf course.

It is also possible, Lord said, that Prior may have inhaled it when swinging the golf club since the action could have caused an aerosol spray effect from the chemical on the tee.

Daconil has been approved by the Environmental Protection Agency, said Henry Jacoby of the EPA's pesticide office.

While it is known to be a "skin sensitizer" because it can cause allergic reactions, Jacoby said, there is "nothing to indicate the use of it would cause any reaction like what happened to the man who died."

Liza Prior, 30, who owns a needlepoint shop in Georgetown, said it was "very devastating" to watch her husband languish in pain for 10 days before his death last Sept. 16.

The couple had married in 1980 and "he was thinking of possibly going to law school. He had just taken his boards and had scored very well. He was very bright and a very good athlete," she said.