Army agents carrying suitcase atomizers sprayed unsuspecting travelers at National Airport with common bacteria 20 years ago, declassified documents revealed this week, in an experiment designed to gauge the nation's vulnerability to an enemy-launched epidemic of smallpox.

The experiment, one of a series first made public in 1977, was part of the Army's highly secret biological warfare research conducted between 1943 and 1971 at Fort Detrick, Md. and, a microbiologist said yesterday, may have been more potentially harmful to those sprayed than scientists realized at the time.

The bacteria used in the experiment, Bacillus subtilis, "is in the air all around us and won't harm a healthy person," said Dr. Arthur Saz, professor of microbiology at the Georgetown University Medical Center.

But in infirm or elderly persons, whose immune system is impaired, heavy concentrations of the "opportunistic" microorganism can produce potentially complicating infections, Saz said. "We know more about such substances now. You couldn't do such an experiment legally today."

Saz was questioned about the experiment after the Church of Scientology released government documents this week detailing experiments mentioned only sketchily in testimony during intelligence oversight investigations in Congress seven years ago.

Sylvia Stanard, a spokesman for the Scientologists, said the organization obtained the documents under the Freedom of Information Act two years ago and has been studying them ever since.

She said the material was sent to the House subcommittee on investigations and the House committee on science and technology after the Army recently requested funds to expand its biological warfare defense facilities at Dugway Proving Ground in Utah.

Both the United States and the Soviet Union signed a 1972 treaty banning biological weapons, but research continues on both sides. The Soviets are reported to have used poison gas or chemicals in the war in Afghanistan.

"The Pentagon says it is only interested in defensive studies at Dugway, but this was a defensive study at Washington National and it may have been harmful," Stanard said. "We don't want innocent people being used as guinea pigs."

An Army spokesman said yesterday that the tests in question were fully listed in the two-volume report released in February 1977 and declined further comment saying there were "no new developments to report."

Declassified documents made public during the mid-1970s disclosed that the Army and the Central Intelligence Agency triggered mock epidemics during the 1960s by spraying such targets as Chicago and New York subway passengers, and even "assassinated" President Richard M. Nixon with germs via the White House air conditioning system.

Details on the "attacks," however, have been few.

The Army's "Miscellaneous Publication 7" from Fort Detrick, which the Scientologists obtained, sought to prove how relatively simply an enemy agent might scatter smallpox through the United States with less than an hour's work in an urban airport.

Using five suitcase-housed aerosol generators and an equal number of disguised air samplers, the agents sprayed bacteria in the North Terminal and then tested various locations in the terminal for effective dispersal of the germ.

"It is emphasized that the five trials, including the sampling procedures, were completed without challenge or question," the document states. "No terminal employee, passenger or visitor gave any outward indication of suspicion that something unusual was taking place."

Outbound passengers would carry the germs throughout the country, the document says, and "numerous secondary cases of smallpox could be expected from extensive exposure of people to the primary cases before diagnosis was made."

The document, whose authenticity was not challenged by the Pentagon, reports a similar experiment at the District Greyhound bus terminal, and paints similar scenarios for simulated attacks at bus stations in Chicago and San Francisco, though it was unclear whether any sprayings in those cities actually took place.

The Scientologists released with the documents a publication from the Society for General Microbiology, identifying the substance actually sprayed, Bacillus subtilis, as a newly suspected agent in food poisoning and operating-room infections.

Georgetown Medical Center's Saz confirmed that the commonplace organism, once thought benign, has become viewed as a complicating factor for patients "already medically compromised."

At a certain stage in its growth, he said, the bacillus produces an enzyme that is toxic to penicillin.

Healthy scientists or technicians spraying it, he said, would be unaffected, but those walking around with cancer, heart disease or a host of other ailments could be affected, depending on their degree of exposure. He declined to estimate how many such people might populate an average airport, but said "in any thousand people, you know there will be some."

The airport experiment's estimated exposure rate of 560,000 to 837,000 organisms per person "is not a hell of a high exposure rate," he said. But he said were the same number of streptococci sprayed on a healthy throat it might be enough to produce a strep throat.

There was no indication in the documents that anyone ever got sick from the sprayings, but then, Saz pointed out, there was no medical reason for any follow-up study at the time.

As for Fort Detrick, it was closed in 1972 and turned into a center for cancer research and genetic engineering. One of its first guests was Soviet Minister of Health Boris Petrovsky, who was shown the transformation as dramatic evidence of U.S. desire for detente.