On Dec. 5, I heard on the radio President Reagan saying that what struck him at the summit was the recognition of how beneficial it would be if there suddenly arose a threat to the United States and to the Soviet Union from some other planet in the universe.
It should be brought to the President's attention (and to those of his audience to whom this point of view appeals) that we already have enough common threat to worry about--that posed by the nuclear weapons, which we have together researched, and together developed and together built, just as if our own nuclear weapons were pointed at ourselves and the Soviets at themselves.
Furthermore, we have the urgent threat of understanding and countering AIDS and perhaps other new diseases, and the challenge of understanding and countering old diseases like cancer, Alzheimer's, and circulatory disorders.
And we have very little time to prepare (whether we solve these problems or not) for continued productive life, with freedom, in a world in which high-quality, easy-to-find and exploit, fuel and minerals are being exhausted. These are major responsibilites of U.S. government, which we are not now fulfilling. Not one of us can count on escaping (and having one's family escape) destruction by nuclear war, painful death by AIDS or cancer, and it is well within our power to do something about each of these problems.
Our goal can well be to improve our individual lot by the material and spiritual reward that comes from contributing to improving the lot of our fellows, rather than from helping some of them benefit by exploiting others.
The old joke may be instructive: "One communist to another: 'Do you know the difference between capitalism and communism?' Other communist: 'No.' First communist: 'Well, under capitalism, man exploits man; while under communism it is quite the other way around.' "
Why delay joint efforts against the common dangers? A threat from another planet would be less serious than those we already face.
RICHARD L. GARWIN
Yorktown Heights, N.Y.