Soviet carelessness over nuclear safety at the Chernobyl plant has shocked the international community, particularly our European allies. These allies, the same ones President Reagan has tried so hard to recruit for his Strategic Defense Initiative, also face a rude awakening about Soviet nuclear practices in space. The prospect of hundreds of Chernobyls in space may well affect President Reagan's chances for selling them and us on Star Wars defenses.

The president is presenting Star Wars as being nonnuclear, meaning no nuclear weapons will be used in the defense. The administration has glossed over the fact that those energy beam weapons envisioned for a space-based defense would require massive sources of electrical energy, and the prime candidates are nuclear reactors -- big nuclear reactors.

SDI officials, who want to triple the budget for next year for research on space power systems, have told Congress that their energy beam weapons may each need hundreds of megawatts of power in space. (Chernobyl produced 1,000 megawatts.) In addition, the latest SDI plans show energy beams will also be needed to distinguish Soviet warheads from decoys and may actually be used to maneuver our satellites.

Granted, some lasers may be ground-based and their beams bounced off mirrors in space. Also envisioned are ground-based "pop-up" lasers, which are nuclear bombs (contrary to the nonnuclear label) that would be shot into space to emit beams of X-rays when exploded. Nevertheless, our SDI calls for hundreds of satellites in orbit, each of which would have electrical power needs. Nuclear power in space will likely supply that electrical power.

I enthusiastically support our civilian nuclear industry here on the ground. I can calmly contemplate our military launching reactors, even big reactors, on rockets into orbit, although the recent rash of fiery rocket failures gives me pause. (At the moment we cannot confidently launch any large payload into orbit.)

I understand that we encapsulate our nuclear power sources to withstand safely even a rocket's catastrophic explosion on the launch pad. We place nuclear power sources only in high orbits, known as "nuclear-safe orbits," where, even if left untended, it would still take hundreds of years for the satellite's orbit to decay to the point of falling back to earth. Meanwhile, the dangerous radioactivity would have died out.

What makes me uncomfortable is the prospect of the Soviet Union's placing hundreds more nuclear-generating stations in space, some of them massive nuclear reactors supplying power to energy beam weapons. Currently, the Soviets put nuclear power sources on board one type of satellite launched into low-earth orbit, and every few days, if everything works well, the satellite is kicked to a little higher orbit to keep it from falling to earth. At the end of the satellite's mission the nuclear power source is transferred to a "nuclear-safe" orbit.

Unfortunately, malfunctions occur. The Soviets' nuclear power sources have been known to fall out of orbit. That happened in Canada in 1978, and the device broke up in reentry, spilling nuclear contaminants on the ground. In 1983 another Soviet nuclear power source dropped out of the sky in two parts; one fell in the Indian Ocean and the other in the south Atlantic.

Ironically, the really large reactor probably does not pose a severe safety hazard, although officials may find it difficult to convince the public of that if one is about to rain down on their country. It's not the uranium in nuclear reactors that's so radioactive, but rather the products of uranium fission. Serious fission does not begin until the reactor starts up. The big reactors that would power, for example, a neutral particle beam weapon in space wouldn't be run at full power for any length of time, unless we were at war. One important exception might be if satellites were maneuvered by nuclear electric propulsion, in which case the large reactors might be used extensively and become highly radioactive.

It's the smaller, much more numerous, station-keeping nuclear power sources that would be the real headache. These would supply day-to-day power for the satellites for surveillance, tracking of objects and communication, and would become quite radioactive.

If we press for Star Wars defenses, it stands to reason that the Soviets will match our hundreds of satellites with similar Soviet defensive constellations, most, if not all, nuclear powered. When it comes to nuclear reactors in space, you don't want a sloppy adversary or even peacetime can become a nightmare.

The details of President Reagan's vision of Star Wars are only now coming into focus. It remains to be seen whether we and our allies will regard the "nonnuclear" label as a cherished attribute if it means hundreds of Chernobyls in space.