In the national debate over air pollution, "acid rain" has special significance. A pollutant that has killed fish in hundreds of lakes in the northeastern United States and Canada, it also falls in the Washington area, but apparently with little effect because the soils and rock formations here contain chemical substances that tend to neutralize the acid.

Acid rain means normal rain or snow containing sulfuric and nitric acids formed in the air mainly from emissions of power plants and factories burning coal and oil. The acid is often blown by winds hundreds of miles from its sources before falling to earth.

This phenomenon wasn't appreciated a decade ago when the nation began seriously cleaning the air. Tall smokestacks -- including some at power plants in the Washington area -- were installed to solve local pollution problems. It wasn't until later that people realized this didn't really help: It merely sent the smoke higher into the air, where wind caught it and transferred the problem elsewhere.

To combat acid rain today, clean air laws set limits to power plant and factory emissions, or require them to burn low-sulfur coal and oil. This costs enormous amounts of money -- the price the country pays for cleaner air and live fish.

In the Washington area, for example, the Potomac Electric Power Co. received variances under one of these laws allowing it to burn dirtier 2 percent sulfur coal instead of the normally required 1 percent in two of its big Maryland generating stations. The company estimates the variances save each of its customers $68 a year.

Rain in the Washington are is more acidic than in many areas of the country, but not as acidic as in New England, the Adirondack Mountains of New York State and eastern Canada, according to John Miller, a deputy director of air resources for the National Oceanic and Aeronautic Administration.

Miller said that acid rain doesn't kill fish here because the limestone bedrock and soils "buffer the lakes" with acid-fighting chemicals.In the northern areas, however, the granite base and shallow soil lack this neutralizing ability.

Miller thinks the acid affects building materials and Washington's statues and monuments. "It does eventually dissolve the stone," he said, adding that in the case of the Washington monument this "would take thousands of years . . ."

The effects of acid rain are not fully understood, even by the experts. The latest report of the President's Council on Environmental Quality said acid rain may be damaging to forests, crops and soils as well as fish. Scholars at Virginia Tech suspect that acid rain from the Ohio River Valley and other heavily industrialized areas may be harming forests and crops in Virginia.

Yet the U.S. Environmental Protection Agency reported early in 1980 that acid rain doesn't hurt yields of most food crops and actually helps many. Tomatoes and strawberries were found to thrive in acidic soil.

Acid rain is a problem in many parts of the world. Acid from the factories of central Europe kills fish in Scandanavia, and much of the acid that falls here and northeast of here comes from the factories and power plants of the Midwest. Researchers suspected acid rain after fish died mysteriously in 14 lakes in Sequoia National Park.

The New York State Bureau of Fisheries estimates that acid rain and snowfall have wiped out all the fish and many plants in half the high mountain lakes in the Adirondacks. The Canadian government estimates fish in 48,000 lakes are in danger of extermination in the next 20 years from acid rain.

The subject is a major diplomatic issue between the United States and Canada. Canada is concerned about U.S. plans to accelerate conversion of oil-burning power plants to coal, fearing this will add to the problem because burning coal produces more pollutants than equivalent amounts of oil.