A cloud of noxious gas, which eyewitnesses said drifted away from the Bluegrass Army Depot about four miles south of here, sent about 30 to hospital emergency rooms and kept I-75 blocked for nearly two hours early today.

Kentucky state police reported that the victims, including three policemen, complained of nausea and breathing difficulties. Most received oxygen treatment at local hospitals and were released. One person remained hospitalized at the Berea Hospital, 13 miles south of Richmond, but was listed in satisfactory condition after being treated for inhalation of toxic fumes.

The pilot of a state police airplane dispatched to the scene said the cloud was about a quarter of a mile long and 500 feet wide. It hovered over the highway and the rural community of Peytontown for approximately two hours before being dissipated by winds. The cloud also covered a rest stop on I-75 about five miles west of the depot, where several stopped motorists inhaled the fumes.

Concerned that the cloud had been caused by a leaking tank truck, state police kept I-75 between Richmond and Berea closed until the cloud had dispersed some time after 2 a.m.

Col. Tom Munnelly, commander of the Army installation that stores a variety of army ordnance, said this morning that he did not believe the gas originated from the depot. He did say that personnel there were burning smokepots, which are used as tactical smoke screens, during the night.

According to reports Munnelly said he received, "the prevailing winds at the time were from the south and the area affected by the chemical is directly to the west."

At the time Munnelly spoke, no one from the area between the depot and I-75 had reported inhaling the gas, which he said tended to show that it had not come from the depot.

Later in the day Gilbert Ellis of the Kentucky fire marshal's office interviewed several motorists who had been traveling on U.S. 421 and U.S. 25 between the depot and the interstate, who said they had passed through the cloud.

Madison County Attorney Thomas J. Smith II told the fire marshal's investigators that he was traveling south on U.S. 421, which runs adjacent to the depot, shortly after midnight, when his car passed through a dense cloud, which caused him to choke and cough.

Depot officials told the fire marshal investigators that the smokescreen gas is primarily composed of three chemicals, grained aluminum, zinc oxide and hexachloromethane.

Soldiers who pass through such a smokescreen during manuevers are instructed to wear gas masks. Concentrations of the gas above 400 parts per million are considered dangerous, depot officials said.