Sputnik's anniversary today reminds us that crucial choices must now be made about U.S. activities in space; someare already being made by default. These choices include the exploration of the solar system, the prospects of Soviet-American agreement not to damage or killeach other's satellites, and the possibility of deploying a gigantic stsyem to destroy ballistic missiles in flight.

Various scientific, civil and military functions can be carried out from space -- often but not always better than from the surface or atmosphere of the Earth. Many of the civil and military functions overlap -- in navigation, communication and weather satellites. Acquiring satellite data on Earth resources has something in common with military intelligence-gathering. But the frequency, timing, geography and fineness of detail required are completely different. Early warning of a missile attack by detection of the infrared signal emitted from a missile exhaust is a peculiarly military requirement.

Even when the requirements have much in common, the differences will sometimes dictate separate military systems, though the military often can and should use civil systems, as it does on Earth. U.S. military space activities now outspend civil ones, not because the former are too large -- yet. The latter have shrunk too far.

By and large, the United States is ahead of the U.S.S.R. in these military support uses for space; in general, the Soviets, by virtue of their geographically central position, have less need to rely on space-based systems for such support. There are exceptions to each judgment -- radar surveillance of the oceans is one. But overall there is good reason for the United States to avoid having space become a scene of active combat.

In space, unlike the seas, it may not be too late to limit by agreement the threats to its free use before those threats are fully developed. Greater U.S. reliance on space, and the likelihood that the United States could if necessary bring enough technological abilities to bear in space wars to win, could well provide motives for each side for such an agreement.

The Soviets have spent a decade working on a limited anti-satellite capability, capable of intercepting low-altitude satellites. Their system, which consists of only a few launchers and vehicles and has experienced occasional failures, is now in being. The United States has countered with the development of a system, scheduled for tests at the end of this year, with considerably more capability and flexibility.

In my judgment, the value from the U.S. point of view of a few such vehicles, or even of the development program itself, is to get the Soviets to agree to a rollback to zero anti-satellite (ASAT) capability on both sides, or to deter them from using such a capability in times of crisis.

The ASAT negotiations of 1978 and 1979 made only marginal progress. One difficulty is that vehicles suitable for launch of satellites are also suitable for launch of satellite killers. Moreover, high- energy lasers from the ground or from space can be used for anti-satellite or other military activities. Adequate verification of an anti-satellite agreement is likely to be more difficult than adequate verification of a strategic arms agreement, because a few anti-satellite vehicles can cut a substantial swath in the satellite capabilities at which they are aimed, while a few ballistic missiles more or less make very little difference to the balance.

Thus, it may be that the best that can be hoped for from ASAT negotiations would be 1) a declaration that attacks on satellites are a hostile act prohibited in peacetime and 2) limitation -- for example, to low altitudes -- on development and deployment of anti-satellite capabilities, consistent with what can be adequately verified. The United States should press to resume such negotiations.

In recent years, some enthusiasts for space wars have proposed all sorts of space-based systems involving such ideas as particle beams, lasers and multiple warheads. Many of the individual technologies required for such systems are far from being demonstrated. Most of the proposed schemes require combinations of several such new technologies into a complex system; some would entail enormous costs.

A space-based chemical laser deployed in a satellite to defend the satellite itself is probably feasible within the next five years. A system of such satellites to defend not only themselves but other satellites would cost some billions, but could probably be feasible in a decade. A system of space-based lasers to intercept ballistic missiles would probably not be feasible before the next century, if ever, and would cost on the order of $100 billion. Moreover, by the time it was deployed, countermeasures against it would be possible, at lower cost, to prevent the system from operating as a successful ballistic missile defense.

My expectation is that the financial limitations under which the Defense Department is again laboring will prevent any such system from being mounted. But it is less clear that its enthusiasts can be prevented from spending some billions of dollars in a fruitless attempt.

Finally, a word is in order on the evisceration of the planetary exploration and space science programs. These are human and intellectual adventures for whose achievements U.S. technology and determination will deservedly be remembered a century from now. The potential terrestrial applications of space-based astronomy, from the understanding of planetary atmospheres and geological processes and from the knowledge of the birth and evolution of the universe, are also real, though less predictable.

Both the planetary exploration and space programs have been decreasing in funding at an accelerating rate over the last decade. Under budget now projected, it is like that the ability to carry out such programs will be lost for the rest of the decade. In that case, it would take most of another decade and many billions of dollars to rebuild it.

At a time when U.S. technology is one of the few comparative advantages that this nation has, and one of the few instruments of American prestige and morale, it is foolish to let the space science and planetary exploration programs wither. The contrast with the proposals for technology and militarily dubious multi-billion-dollar space weapons programs is all the more painful.