COAL IS this country's most abundant domestic energy resource--and its greatest source of dirty air. The technologies for using it are among the world's oldest--direct combustion is essentially the same today as it was 700 years ago --and, increasingly, among the newest and most advanced. These paradoxes abound. The most important one is this: with one exception the choices made in the near future, in revisions of the Clean Air Act and in the allocation of scarce energy research funds, will largely determine whether coal can eventually replace oil as the country's dominant energy source.

The exception concerns the buildup of carbon dioxide. If the use of fossil fuels is causing the earth's atmosphere to heat up, and if the consequences of that heating turn out as many scientists are now predicting, there will likely be no technological fix. Then the choice will be between abandoning the use of fossil fuels and restricting their use to what is absolutely necessary.

Coal burning is the largest, or one of the largest, sources of most of the currently controlled forms of air pollution, especially of particulates (ash or soot) and sulfur dioxide. It is also the primary contributor to acid rain, a new and still uncontrolled type of pollution. Nevertheless, coal production grew by 25 percent in the last five years, and the Department of Energy projects that it will double from today's level by the end of the decade. The question that underlies the forthcoming debates over the Clean Air Act is whether the large price difference between coal and oil--now 10 times greater than in 1973--can cover the costs of systems needed to make such heavy use of this dirty fuel environmentally tolerable.

In corporate board rooms and at the Department of Energy the issue is whether to bet on the currently available technologies for making synthetic fuels from coal--many of which date back to the last century--or to concentrate on still highly speculative but potentially far more attractive new methods. These second-generation technologies include possibilities for both increasing the amount of energy that can be extracted and eliminating most of the air pollutants. They range from liquid mixtures of coal that can be transported and burned like oil to underground mining methods capable of converting coal directly to clean-burning gas.

Coal is poised to move from technological backwaters to the forefront of sophisticated technology. But in the long run it will only be able to fulfill its promise as this country's greatest energy resource if its pollution problems are solved first.