Army scientists sprayed "harmless" bacteria directly onto New York subway riders in a 1966 test throughout downtown and midtown Manhattan, according to a Defense Department report made public yesterday.

The commuters paid little attention, the Army said in the study, which concluded that subway systems were ripe targets for "covert biological attack."

Details of the experiment, previously disclosed only in broad outline, were contained in a 71-page report of the Army's Special Operations Division at Fort Detrick, Md. It was released under the Freedom of Information Act in response to a request by the Church of Scientology.

The simulated biological warfare attack in New York, conducted from June 6 to June 10, 1966, included the release of aerosol clouds of a test bacillus into stations along both the Seventh and Eighth Avenue lines.

In these trials, one of the Army's observers reported, small quantities of "a harmless simulant agent," known as "bacillus subtilis var. niger" were inserted through the sidewalk gratings, producing "aerosol clouds" that "were momentarily visible in the station" below.

"When the cloud engulfed people." the observer continued, "they brushed their clothing, looked up at the grating and walked on."

The whoosh of the trains carried the stuff uptown and downtown within a few minutes, the report said. Even more effective, the Army found, was dumping bigger doees in subway tunnels, where light bulbs containing the bacillus were tossed from moving trains.

The tests were conducted without the knowledge of either New York police or the New York City Transit Authority, but the Army's personnel went virtually unchallenged despite their assiduous collection of air samples with portable pumps and other devices.

The closest call, according to the study, came when one of the Army's operatives from Maryland walked into a station smoking a cigarette.Challenged by a police officer, he said he was from out of state and produced a phony letter saying he was employed by an industrial research organization. Copies had been given to all test personnel "as a cover in case they were questioned," the report notes.

According to the report, which cited the existence of subways in the Soviet Union, Europe and South America as well as the United States, the tests were conducted not only to assess the vulnerability of subway systems to covert biological attack, but also to determine "methods of delivery that could be used offensively."

Emphasizing the rapid spread of the test bacillus from the lightbulbs, which were also tossed along the Lexington Avenue line, the study found:

"Dropping an agent package to the roadbed from a rapidly moving train is an easy and effective method for covert contamination of a segment of a subway line with a biological agent. . . . [It] is aerosolized and dispersed rapidly by the movement of trains, penetrating stations and trains in the area and persisting there for one hour or longer."

The Army concluded: "Simultaneous or near-simultaneous deposit of a pathogenic agent in one or more locations in each of the several subway lines operating in midtown Manhattan at a peak workday traffic period would expose a large number of people to infection and cause high casualties among the population working in the area."