ACID RAIN is a real phenomenon, and a dangerous one. It kills aquatic plants and wildlife, reduces harvests of economically important food and timber crops, corrodes buildings, affects human health, leaches vital nutrients from the soil and causes the release into ground water supplies of poisonous metals such as mercury.

It is a man-made phenomenon; about that also there is little doubt. There is what the National Academy of Sciences called "little probability" that the source of acid rain is something other than the oxides of sulfur and nitrogen that are emitted by power plants, smelters and, in the case of nitrogen, automobiles.

But a direct link between these emissions and acid rain has not yet been conclusively demonstrated. There is only, again in the words of the academy's report, "overwhelming circumstantial evidence." This is because little is known about the complex chemistry and meteorological events that convert these precursors into acid precipitation and can deposit them thousands of miles from their source. It is not known, for example, whether there is a one-for-one connection between an additional ton of emissions and an equivalent amount of acid rain, or whether the relationship is a more complex one.

Because of this uncertainty, the Reagan administration opposes actions to control acid rain. Energy Secretary James Edwards says acid rain is nothing to worry about. Others argue that more research is needed before controls are justified. Environmentalists, many scientists and the Canadian government believe that the damage already being done more than justifies controls, even if they later turn out not to have been the best choice. The National Academy said: "the picture is disturbing enough to merit prompt tightening of restrictions on atmospheric emissions."

In response, the White House has taken the National Academy of Sciences off the case. It has cut off funds to continue the acid rain studies. James McAvoy, a White House environmental adviser now at the Department of Interior, questioned the academy's ability to do an "objective review." And a plan under which the academy and its Canadian counterpart would jointly review technical documents that are to be the basis for a U.S.-Canadian treaty on acid rain has been dropped. Instead, the White House has appointed a different panel of scientists to review the subject, and preparations for the treaty negotiations are proceeding slowly.

The president is certainly entitled to appoint his own panel of experts. But this has been done in a manner that is far from reassuring. Only by setting a prompt deadline for the panel's completion of its work and by taking steps to ensure that the panel's findings are properly and objectively evaluated can the White House hope to allay the anxieties it has created