Reports from the National Academy of Sciences indicate that the earth's ozone layer is still seriously threatened by the chemical compounds known as fluorocarbons. The academy found that the ozone layer, a protective shield 15 to 20 miles above the earth, will eventually diminish by about 16 percent unless further controls are imposed on the use of fluorocarbons. As the ozone layer diminishes, more of the sun's ultraviolet rays will reach the earth's surface, causing effects that range from increased numbers of skin cancers to subtle but critical alterations in the ability of plants and animals to survive.

To put matters in perspective, the likely net ozone loss is now more than twice what the academy predicted in its 1976 report that led to a federal ban on the use of fluorocarbon aerosol propellants.

Fluorocarbons are useful chemicals with a wide variety of industrial and commercial applications in addition to their use of aerosol propellants. They are, for example, nearly ideal refrigerants for products such as commercial air conditioners and freezers, and are used widely in the process of manufacturing urethane foams found in products such as mattresses and furniture.

These new academy reports reinforce the need to resolve an important outstanding issue in the control of the production and use of fluorocarbons. That issue concerns the fact that while the United States took prompt action to limit nonessential uses of fluorocarbons, the rest of the world paid little heed to the danger. Only Sweden and Norway have joined us in banning nonessential uses of fluorocarbons. Recently, the environmental ministers of the Common Market agreed to a 30 percent reduction in the aerosol uses of fluorocarbons. But, in the meantime, worldwide fluorocarbon use has grown to such an extent that it has cancelled the effect of the U.S. ban. The world is consuming just as many fluorocarbons as it was before the United States phased out aerosol uses.

The reasons why the rest of the world has taken little action are varied. But the most important seems to be a general sense of skepticism about whether fluorocarbons really diminish the ozone layer as the scientists predict. The skepticism stems, in large part, from the fact that the predictions of ozone loss from fluorocarbon release are based on mathematical models rather than actual measurements.

One way to convince the doubters would be to wait for actual measurements to demonstrate ozone loss. However, there are grave risks in this "seeing is believing" approach. In particular, since natural fluctuations in ozone density are large enough to mask the first small decreases caused by fluorocarbons, only a substantial overall decrease would allay the lack of confidence in current predictions.

Moreover, waiting until such a large decrease can be actually measured adds further risk because there is a significant time lag between the release of fluorocarbons and ozone destruction. Even if all new releases were halted instantly, the ozone layer would continue to decrease for another 15 years before reaching equilibrium and the start of its slow recovery.

New limitations of fluorocarbon use in this country are under study by several federal agencies. But further domestic regulation will be more difficult and less popular because substitutes for industrial uses may not be as readily available as they were for aerosol propellants. Moreover, U.S. regulatory action alone cannot end the threat to the ozone layer. At the peak of fluorocarbon use in this country, the United States controlled only about 50 percent of world use of these chemicals. Our share is now much less.

The rest of the world must be convinced that the threat from fluorocarbons should be taken seriously. It is critical that they look at the available scientific evidence as carefully as we have. Unless they do and take preventive action now, we may all see the day when the density of the ozone layer will decrease to the point where direct measurements can be substituted for predictions from mathematical models. At that point, finally, the whole world will be convinced that the sky is falling. And, at that point, it will be too late.