BECAUSE THE United States has gigantic reserves of coal, it has an urgent national interest in finding ways to use it without poisoning the atmosphere. The demand for electricity is rising, and the country has backed uneasily away from nuclear energy to generate it. Conventional coal-fired power plants pump enormous volumes of pollution into the air. But there's an alternative. Pepco has announced that it is going to begin using a better technology -- the first utility in the country to commit itself to a process that turns coal into gas to run its turbines.

The newer coal-burning plants run the smoke through scrubbers that eliminate about 90 percent of the pollutants. But the remaining 10 percent includes a number of dangerous ingredients. Unlike burning, the chemical process of turning coal into gas is essentially a closed system and eliminates the fine particles of ash that are the greatest health hazard in coal smoke. Rather than lofting it into the atmosphere, gasification takes the sulfur out of coal in solid form -- and pure enough that Pepco will be able to sell it commercially. Nitrogen oxides are another component of acid rain, and gasification produces one-third as much nitrogen as burning coal.

Pepco plans to install this equipment on the site of its present plant in Dickerson, Md., beginning, around 1994. At first the turbines will run on natural gas or oil. Then Pepco will step up power by using the turbines' hot exhaust to make steam, and adding steam generators. Finally, sometime around the turn of the century -- the timing depends on the need for electricity in this area -- it will introduce the equipment that turns coal into the gas that will fuel the whole system.

Technology doesn't always move quite as quickly as you'd like. The actual introduction of gasification is still at least a dozen years off. But it's not an experimental process. A pilot plant sponsored by, among others, the Electric Power Research Institute has been in very successful operation in Southern California for three years. The utilities wanted to see it up and running, over an extended period, before any of them was prepared to commit itself to the idea. But now Pepco has decided to go forward with it -- an innovation that deserves attention in a country that's having trouble reconciling its requirements for electric power with its increasing determination to protect the quality of its air