PRESIDENT CARTER's proposal that the United States and the Soviet Union agree not to put nuclear reactors into orbit around the earth has much popular appeal. The crash of Cosmos 954 has demonstrated the potential dangers that one of these devices can create. That its debris came down in a sparsely inhabited part of the world was pure luck. It might have landed on the White House or the Kremlin. And it might have released substantially more radioactive material than it now appears to have done.

Nevertheless, there is likely to be considerable difficulty in getting the Soviet Union to accept a proposal like the one the President made on Monday.Mr. Carter appears to be suggesting an agreement that would require us to give up nothing we are now using but which would require the Russians to give up a kind of equipment that has been central to their military reconnaissance program.

Cosmos 954 is believed to have been a radar-carrying satellite designed to keep track of the American naval fleet. It is one of a series of such spacecraft that the Russians have used to watch American and NATO military operations. Several of these have been powered by nuclear reactors electricity in space - solar cells, batteries and radioactive isotopes - generate insufficient power to run the equipment the Russians use. The United States has chosen not to use such energy-consuming equipment in space, at least in part because the geography of American outposts makes the same kind of reconnaissance possible by more conventional means.

Thus, the problem presented by Cosmos 954 is more that just a problem of safety. It is also tied to the uses of space for military purposes and to questions of arms control. Satellites that look down on the military operations of other countries and thus give a country some degree of confidence that it knows what an adversary is up to have had a relatively stabilizing effect on world politics; and such satellites will have a role in any inspection system to police a SALT II agreement. It is possible, of course, that technological developments can make obsolete the use of nuclear reactors on such satellites or can create the foolproof satellites of which Mr. Carter also spoke. But the odds are that spacecraft like Cosmos 954 are going to be around for some time.

This being so, it surely is time for some serious thinking about what can be done when satellite - or anything else left in orbit by a space mission - goes out of control. Even nonradioactive pieces of metal could cause considerable damage if they landed in, say, the stands of Kennedy Stadium during a Redskins game. Within a few years it may be possible to prevent crashes like that of Cosmos 954 by corraling or destroying the errant satellite. One of the first missions of our space shuttle will be to change the orbit of Skylab so that it will not tumble down. And the one peaceful use of the satellite-killing weapons that appear to be under development would be to destroy a straying satellite. But before either nation could safely corral or destroy a satellite put in space by the other, there would have to be even more space cooperation than was displayed in recent weeks. Without such cooperation the problems highlighted by the crash of Cosmos 954 are likely to be with us for a long time.