The Pentagon papers are being burned, under guard, where they produce a lot more heat and hot water for the Defense Department.

Daily, more than 10 tons of classifeid documents, ones that cannot be pulverized into paper pulp and recycled, are being burned in a small metal barn a coal lump's throw from the eastern most side of the Pentagon.

The new incinerator, beside the Pentagon's coal-fired power plant, not only solves a 20-year-old "secrets" disposal problem for the Pentagon and numerous downtown Washington military offices, but provides nearly 25 per cent of the heat and hot water needed for more than 22000 Pentagon employees. It will save the Defense Department an estimated $250.000 a year.

A similar but much larger trash-to-heat system is being studied by Pepco and District of Columbia officials in which steam would be produced at the city's huge Benning Road incinerator and pumped next door to help make electricity at Pepco's generating plant.

The six-months-old incinerator already is a roaring success with Defense officials, not only because it saves money evaporating secrets, but because it creates virtually no air pollution.

"EPA (the Enviromental Protection Agency) checked it and it far surpassed their greatest expectations," Pentagon security cheif Sam Carmell proudly pro-claimed claimed. "There are no visible emissions. You can't see a thing coming from the two stacks execpt occasional heat waves."

It's also more secure to truck secret documents 100 yards to a guarded incinerator than to haul them around town said Carmell.

Remember that Air Force truck that crashed on 14th Street Bridge and spilled classfied documents all over the bridge and floating down the Potomac?" he said.

For the paset 20 years the Defense Deoartment daliy has been trucking up to 10 tons of classified computer print outs, typewriter ribbons, films, plastic tapes and other non-recyclable paper products to assorted incinerators around Washington, and guarding them until they were burned. Officials became desperate last year because most of the incinerators are being closed by EPA for causing air pollution. Carmell said. "And then we found this."

"This is a 20-ton-a-day incinerator built by a Mechanicsville. Va., company. Air Pollution Control Products Inc. The company has incinerators in 34 U.S. cities "such as Salem, Va.; Orlando, Fla., and Hot Springs, Ark, mostly cities under 150,000 population and most converting trash and garbage into steam that they use or sell," said company vice president Lee Wiles. The incinerators also can be made to produce electricity or even air conditioning, Wiles said.

The Pentagon incinerator, which operates only eight hours a day at half its capacity, produces between .05 and .08 grams of particulate matter per cubic meter of flu gas, according to Wiles. A spokesman for EPA said this week that he believes that the Pentagon plant actually was inspected for EPA by environmental officials of the Army stationed at Edgewood, Md., Arsenal, but that its emission levels appeared to be below the level the EPA requires for large new incinerators - which is no more than .18 grans of particulates per cubic meter.

The $212.000 cost of the incinerator - the building, a security vault and some minor road work cost another $106,000 - should be recouped in the first year since until now it has cost about that much to haul classified trash to nearby incinerators, such as those at Andrews Air Force Base and Alexandria, and to pay incineration fees.

At least an additional $50,000 a year should be saved in coal costs at the Pentagon's heating plant next door, because steam produced by the incinerator saves five tons of coal a day, which costs about $50 a ton. The material burned, primarily computer printouts "which aren't pulpable, " said Camell, is soaked with home-heating fuel oil until combustion temperatures reach up to 1.8000 degrees, when the material - fed continuously into the incinerator - burns itself. The maximun fuel oil use is 12 gallons an hour, said Wiles.