The two huge, concrete stacks setm obsolescent, more a symbol of the past than a present necessity. A nearly invisible exhaust gas is the only substance released through them.

Between the two stacks sits a four story building once at the center of an environmental controversy but now a major element in the city's continuing battle to get rid of its solid waste.

There, a sttady parade of garbage trucks (about 190 a day) are weighed and move slowly up a ramp and into a dumping platform. The air is pungent with the stench of thousands of tons of solid waste.

After unloading their cargo into one of two large bins the trucks move down another ramp and out into the city. What they leave behind accounts for nearly half the gargabe produced in Washington.

The site is Incinerator Plant Number One, whose construction and use was fought for years by critics such as former City Council Prtsident Gilbert Hahn, Jr., who contended that the facility pollutes the air and that there are cheaper ways to dispose of solid waste.

The district has revised its air quality standards so that they art no longer violated by Incinerator Plant Number One, but supporters of the plant such as Edward M. Halley Jr., of the Department of Environmental Services say that there rtmains a major problem in the public perception of incinerators.

"Incinerators just have a bad public connotation, it's awfully hard to convert the public," Halley said.

John Schlif, deputy chief of solid waste disposal for the District, remarked: "Some people have been deadly afraid of incinerators, period. They don't realize that the technology is thtre to control the pollution."

Schlif, a chemical engineer who was in charge of the plant when it first opened in 1972, defended itst air pollution control devices.

"We have air pollution equipment in this incinerator that is no different from what is being put in the most modern plants today," he said.

During a tour of the $23 million dollar facility at 3200 Benning Road NE, Schlif and Richard Moreland of the city's waste disposal office explained that the incinerator can burn about 900 tons of garbage a day or about 250,000 tons a year. They said it takes 95 people to operate that plant on a 24-hour-a-day, five-day-a-week basis.

In addition to the incinerator the city hauls about 1000 tons of solid waste a day to a sanittion landfill in Lorton, Va. Both moreland and Schlif agreed that for the moment it is cheaper to use the waste as Landfill rather than burn it, but they said this was a short term solution which would become less viable in the future as the number of dumping sites decrease.

The incinerator reduces solid waste by 90 per cent through a thermal reduction process that leaves a residue made up of ashes, metal, glass, and particles separated from gases.

Usually this residue is trucked away and dumped, but experiments are under way to find uses for the material.

One such possibility, once the residue has been purified, is to use it as an aggregate in asphalt. The Department of environmental Services plans to test the feasability of this by using the residue as a sub-base in paving 14th Streat between W and Cedar Streets SE.

Solid waste enter the system when the trucks dump garbage into one of two 2000 ton capacity bins. The waste is then scooped up by a bucket with teeth that dangles from an overhead crane and is deposited into one of six hoppers for "fteding" to the furnaces.

The intense fire in the furnaces, which burns the garbage at a rate of 20,000 ibs. per hours, is kept going by an induced draft system from giant fans and by the use of 150 per cent more oxygen than is necessary to start a combustion.

The gases produced by the fire rise and enter various chambers where they are cooled. Particles in the gases are removed in a series of steps by mechanical separators and electrostatic precipitators.

The particles from the gases, along with the ashes produced during burning and other matter such as glass and metal then goes to ash removal system that watercools the material. It is then loaded onto conveyor belts and dumped into a truck for shipment. Conveyor belts are used to remove excess water from the material.

Without this system, all the gases and ashes would be spewed out into the atmosphere through the stacks. As it is, only a few remaining hot exhaust gases are now let off into the air.

Talks have been under way between the Department of Environmental Services and the Potamac Electric Power Company to see if the incinerator can be converted into a steam producing plant. If this can be done at a reasonable cost the steam could be sold to PEPCO, which has a generating plant next door, thus saving the utility the money it now spends on oil to produce its own steam.

Pter H. Henziger, PEPCO vice president for generating, said the success of the project would depend on the quality of steam that can be produced and on its cost to the utility.

"If we could get it for the same total price or less by using their steam it would be a benefit to the electricity customer and to the city," Benziger said.

Halley of the Department of Environmental Services emphasized that the talks with PEPCO were in the preliminary stage and added it was impossible to determine now how much the conversion of the plant would cost. The steam would be produced from the excess heat created in the furnaces, heat that is now wasted.

"We're hoping something productive will come from this that will at least convert a wasted product into an energy source," Halley said.

Halley also said the department plans to hire an outside consultant to make a $250,000 study on the entire issue of solid waste in Washington and alternatives for its disposal.