In an experiment designed to determine both attack and defense capabilities with biological weapons, a Navy ship blanketed San Francisco and its neighboring communities with a bacteria-laden smog for six days in 1950, according to U.S. military records.

The records concluded that nearly every one of San Francisco's 800,000 residents was exposed to the cloud released by a Navy ship steaming up and down just outside the Golden Gate Bridge.

The aerosol released by the ship contained a bacteria known as serratia, which was thought harmless by the military at the time but which has been found since to cause a type of pneumonia that can be fatal.

The Defense Department documents and related interviews yesterday indicate that the Army, which sponsoed the testing, never revealed the nature of the experiments despite an outbreak in San Francisco at that time of serratia-related pneumonia.

he documents were released recently to the family of Edward Nevins, a retired San Francisco pipefitter who died during the serratia pneumonia outbreak. Eleven other cases of the disease were confirmed at the time, but all those victims survived.

Nevins' children, grandchildren and great-grandchildren are suing the Army for $11 million. The suit charges that Nevins, 75, died as a result of exposure to the bacteria let loose during the military experiment.

The nature and size of the biological warfare experiment in San Francisco raises questions about similar open-air tests that the Army disclosed in 1977 it had conducted on 239 occasions between 1949 and 1969.

In its 1977 testimony to the Senate health subcommittee, the Army said that 80 of the 239 tests included some sort of disease-producing agent. The tests were conducted in Washington, New York City, Key West and Panama City, Fla., and San Francisco.

An Army spokesman said yesterday he could not determine immediately whether the spraying was similar in all the cities to that done off San Francisco.

According to the documents released to the Nevins family, a Navy auxiliary mine-laying vessel spent six days cruising just outside of San Francisco Bay. Crewmen on the ship released an aerosol contaminated with bacillus globigii and serratia marcescens.

A report, which was classified at the time, said the threefold objectives of the tests were:

"To study the offensive possibilities of attacking a seaport city with a BW (biological warfare) aerosol generated from a ship or other source located some distance off shore.

"To attempt to measure the magnitude of the defensive problem presented by (a) above.

"To gain additional data on the behavior of BW aerosol as it is borne downwind."

The report said the spray covered 117 square miles of San Francisco and neighboring areas. "Nearly all of San Francisco received 500 particle minutes per liter," the report said.

"In other words, nearly every one of the 800,000 people in San Francisco exposed to the cloud at normal breathing rate . . . inhaled 5,000 or more fluorescent particles," the report said.

"Any other area," the report continued, "having a steady wind and a degree of atmospheric stability comparable to San Francisco is vulnerable to a similar type of attack and there are many such areas in the U.S. and elsewhere."

The spraying took place between Sept. 20 and Sept. 26, 1950. The 1951 Army report does not mention it but cases of serratia pneumonia, a rare disease, began appearing almost immediately. Nevins died Nov. 1, 1950, at the old Stanford Hospital in San Francisco.

Nevins' grandson James, a San Francisco attorney, said yesterday that the Army did not notify his family of the reason for the death and apparently did not tell officials at Stanford Hospital.

"In 1951 the doctors at the hospital who treated Edward Nevins and the others wrote an article in the archives of internal medicine expressing puzzlement over the outbreak of such a rare disease," said Jerrold Ladar, the attorney for the family in the case.

The Nevins family found out about the experiement in an article in the Long Island newspaper Newsday in 1976, Ladar said. "All they knew before that was that Nevins went into the hospital for a successful hernia operation and ended up dying a very painful death with clear evidence of serratia in his blood and urine samples."