The Army knew there had been a chemical spill at Fort A.P. Hill in Virginia at least three years before 31,000 Boy Scouts camped there for their national jamboree in 1981, an Army deputy assistant secretary said yesterday.

The spill, which is mentioned in Army records as early as 1977, involved leakage from two 55-gallon drums of the herbicide Silvex in a small shed on the 76,000-acre post. It caused little concern at the time because no one realized that Silvex contained dioxin, Army officials said yesterday.

"At the time, no one knew that it was that much of a hazard. We all used herbicides then," said Lewis D. Walker, deputy assistant secretary of the Army for environmental safety and occupational health.

Walker's account of when the Army knew of the spill confirmed a similar report in Tuesday's Dallas Times-Herald. When use of dioxin-contaminated Silvex was banned one year later, Walker said, the spill at the original storage area had been all but forgotten.

Earlier this year, however, the Army tested the soil around the shed as part of its own nationwide hazardous waste cleanup program. Test results released last week showed levels of 228 parts per billion of toxic dioxin in the soil under the shed and about 3 parts per billion 150 feet downhill from the shed.

Those levels, well above the acceptable risk level of 1 part per billion established by the federal Centers for Disease Control and the EPA, have prompted concern among parents of Boy Scouts nationwide since the Army announced the results last week.

The national headquarters of the Boy Scouts of America has logged hundreds of calls. Locally, parents have called individual troop leaders and the National Capital Area scout headquarters.

"I don't even know what dioxin is," said Frances Schreier, a Kensington mother whose 19-year-old son attended the jamboree.

"How is it transmitted? Is it on his sleeping bag? How dangerous is it? I don't know whether to take him to the doctor's or not. And not knowing, and the worry about not knowing, is really starting to make me angry," she said.

Army and Boy Scouts officials said they intend to see that all traces of dioxin are eliminated before the scheduled return of the jamboree to A.P. Hill next year. The organization has begun mailing letters and a map of the site to families of scouts who attended the jamboree.

Yesterday, Boy Scouts and CDC officials said chances of contamination for scouts who attended the jamboree were extremely remote.

"They should be concerned but they should not worry," said national scouting spokesman Raul Chavez. "On the basis of our information, an 84-pound boy would have to eat 264 pounds of dirt to have been contaminated."

Army and Boy Scouts spokesmen said they believe that few if any scouts entered the shed area, which was fenced off during the 1981 jamboree.

They do acknowledge, however, that jamboree staff members slept on cots within that area and that the shed itself was entered by jamboree staff members who were using the shed to store communications equipment.

National Capital Area Boy Scout director Rudy Flythe said yesterday that scouts from the Washington area were billeted more than a mile from the shed where the spill had occurred.

But one local scout who asked not to be named said yesterday that scouts were encouraged to roam over the entire jamboree area and that many scouts could have come in contact with the dioxin. "The average scout covered the whole jamboree area," the scout said, collecting and trading patches.

Officials from the Environmental Protection Agency and the Army are scheduled to meet today at Maryland's Edgewater Army Arsenal northeast of Baltimore to coordinate plans for more extensive testing for contamination of surface and subsurface soil at A.P. Hill, according to EPA officials.