THE SCIENTIFIC case for controlling acid rain grows increasingly strong. That means further reductions in the air pollution generated by coal smoke. The costs will be substantial, and they will fall chiefly on people's electricity bills, since most of that smoke comes from utilities' power plants. Those costs, and the uncertainty over some of the scientific issues, had made the Reagan administration reluctant to do anything about acid rain. But two reports this week give the administration little choice but to begin moving toward much more stringent controls.

A special committee of scientists appointed by the White House warned it on Monday that waiting for further evidence would risk irreversible damage. Two days later the National Research Council concluded that there is a direct relationship between emissions of sulfur dioxide--which comes mainly from burning coal--and the acidity of the rain that falls in the northeastern United States and southeastern Canada. To cut the acidity of that rain in half, as the NRC urged two years ago, requires cutting sulfur dioxide emissions in half.

Nothing is simple in the chemistry of air pollution, and by no means all of the mysteries of acid rain have been resolved. Why, for example, is the damage from acid rain increasing while sulfur dioxide emissions have been decreasing since the early 1970s? One possibility is that other pollutants from other sources affect the process. Another is that there may be a loading process in the chain of causation, in which pollution's effects become cumulative.

The National Research Council's report draws attention to the disparity between the importance of the scientific choices to be made and the paucity of reliable scientific data on which to make them. For all the controversy over acid rain in the past decade, there is only one place in North America--at the Hubbard Brook Experimental Forest in New Hampshire--where anyone has actually taken accurate measurements over a period of time to track acidity. It is worth noting that recent cuts in the budget of the Environmental Protection Agency have resulted in discontinuing many pollution indicators. Once again the country is about to spend billions of dollars to combat pollution that it has been unwilling to spend a few millions to investigate systematically. That is a familiar theme in the politics of environmental improvement.

Another familiar theme also turns up in these recent reports. Americans tend to regard coal as familiar and therefore safe. But the pollutants in coal smoke carry many risks to human health and to the country's ecology. As Americans burn more of it, they are going to have to do it under increasingly tight rules. Acid rain is only one example of the costs of handling coal carelessly.