While much of the world focuses its attention on the distant danger of what "Star Wars" defense technology might bring, there is a threat much closer at hand. It stems from nuclear reactors being launched into space to power satellites. The Soviets are responsible for the most dangerous practices in this area, but our own government agencies are doing little to call attention to the hazards involved.

On Jan. 23, the main body of Cosmos 1402, a Soviet radar ocean reconnaissance satellite (RORSAT) reentered the atmosphere over the Indian Ocean and may actually have fallen into the sea south of the U.S. naval base on Diego Garcia.

American military and civilian space and science agencies detected the satellite's failure to move to its intended higher orbit and tracked the steady deterioration of its original low-Earth orbit.

Because current Soviet RORSATs are powered by nuclear reactors, the federal agencies instituted a watch, assembled contingency response teams and alerted other nations to the danger that radioactive debris from the satellite could reach the Earth's surface, possibly even in inhabited areas. A similar Soviet satellite, Cosmos 954, had scattered radioactive debris over northwestern Canada in 1978.

Several things suggest, however, that the federal agencies may not have done a good job in informing the public of the dangers of accidents involving nuclear spacecraft and in representing U.S. interests with respect to Soviet nuclear activities in space.

While Cosmos 1402 failed to carry out its command to separate and transfer contaminated sections of the spacecraft into higher orbit, the Soviets were successful, as they claimed during the incident, in separating the reactor core from the main satellite structure. Because of this, the nuclear fuel and most contaminated components on Cosmos 1402--which reentered the atmosphere later on Feb. 7, over the South Atlantic, a thousand miles off Brazil--were not shielded by the structure during recovery and probably did not reach the surface of the Earth.

Although the Soviets claimed the reactor core had been successfully separated, the federal agencies persisted in identifying the chief cause of concern as the possibility that contaminated sections of the satellite would reach the surface of the Earth near settled areas.

The Soviets successfully countered these statements in their press releases by stressing that, since the core had been separated, it would be incinerated in the atmosphere. The Soviets also claimed that the probability of the satellite structure's coming to Earth in an inhabited area was very small, and that even if pieces of the satellite landed near humans, the radioactive contamination of the structure was so minor that even prolonged contact would not result in human doses in excess of the limitations specified by the International Commission on Radiological Protection.

The Soviet reply was probably true. Thus, the Soviets were able to deflect U.S. criticism of their nuclear space practices because the U.S. agencies had based their charges on a minimal and improbable hazard--high human radiological exposures resulting from contact with lightly contaminated fragments.

In fact, however, the Soviet claims were nearly irrelevant to the true hazard presented by the reentry of Cosmos 1402: the radiation returned to the Earth's atmosphere from the satellite's nuclear reactor core. It is extremely difficult to estimate the amount of radioactivity that would reach the natural or human environment as a result of disintegration of a reactor core in the upper atmosphere. Such a core contains thousands, if not tens or hundreds of thousands, of curies of radioactivity from uranium, plutonium and fission products. Much of this radioactivity results from extremely long-lived radioisotopes.

Depending on the altitude and latitude at which this material is injected into the atmosphere, and prevailing meteorological conditions --such as wind currents and rainstorm activity --the radioactive matter could either linger in the upper atmosphere or be distributed over the surface of the Earth--possibly in inhabited areas. A government contractor's worst-case analysis of the potential human health consequences is reported to have resulted in a projection of 40,000 fatal cases of lung cancer. In the case of Cosmos 1402, 1 to 3 cases of cancer are said to be probable worldwide, but this is on the average and could change drastically as a result of specific atmospheric conditions.

At any rate, the background radioactivity of the Earth would be substantially increased by the destruction of a reactor core in the upper atmosphere. In 1964, a U.S. Transit navigational satellite powered by a plutonium power pack called SNAP-9A burned up in the atmosphere over the Indian Ocean when it failed to reach orbit after being launched from Vandenberg Air Force Base in California. The approximately 2.2 pounds of plutonium lost into the atmosphere resulted in a trebling of plutonium contamination levels in the Southern Hemisphere over what had resulted from all nuclear tests. By contrast, Cosmos 1402 and its sister RORSATs carry some 100 pounds of enriched uranium fuel.

Why did the federal agencies focus on the improbable harm that could have resulted from the impact of the body of Cosmos 1402 while playing down or ignoring the hazard of reentry of the satellite's reactor core? Well, Earth impact had been experienced before with Cosmos 954, and the effect of reentry of the separated core would admittedly be very difficult to estimate. The agencies nevertheless lost their opportunity to make telling criticisms of Soviet nuclear activities in space--which are necessarily dangerous since they use relatively large reactors in low-Earth orbits.

One reason, perhaps, is that the agencies did not want the finger pointed back at them. Aside from Cosmos 954 and 1402, the Soviets are thought to have lost three other nuclear-powered spacecraft. According to a New York Times report, an early Soviet RORSAT fell into the Pacific Ocean north of Japan in 1973. And high-altitude radioactivity was detected after the failure of two Soviet lunar missions in 1969.

The United States, in addition to SNAP-9A, has lost two space reactors, but the shielding on these devices is thought to have prevented significant radioactive releases. In 1968, a Nimbus meteorological satellite carrying the reactor SNAP-19 was lost into the Santa Barbara Channel, but the reactor was recovered intact. The lunar excursion module (LEM) from the aborted Apollo 13 moon mission was lost into the Pacific in 1970; its reactor, SNAP-27, is assumed to be intact in the Tonga Trench.

But, sadly, the major reason for the agencies' reticence seems to be that they are so fascinated with their own nuclear plans for space that they were unwilling to criticize the Soviets on the inherent dangers of this technology. The need for higher power levels on spacecraft has led American space planners to call for the development of a space shuttle-compatible 100-kilowatt reactor (compare this to about one kilowatt for current solar cells) that could be adapted to a wide variety of potential space missions. Of these, military applications appear to predominate in current thinking.

The higher power levels that nuclear reactors could provide would permit the development of powerful orbital radars with very good ground resolution. High-powered satellites could also be used for jamming or receiving faint electronic signals. They could be used to generate blue-green laser beams that might be able to communicate with or even detect submarines underwater. Ultimately, they could be used to power short-wave length lasers or particle beams for use against other spacecraft or missiles. (Less effective long-wave length lasers would require cumbersome chemical fuel sources.) Civilian applications will also be forthcoming, including improved remote sensing of natural resources and advanced power systems for deep space probes.

By failing to criticize the inherent dangers of Soviet nuclear practices in space, the federal agencies lost a good opportunity to draw world attention to dangerous current Soviet practices. The agencies also revealed their inabilities and biases, however. The public will inevitably become concerned when the federal government begins to implement plans for nuclear development in space, especially for military purposes. Better that the agencies face the issues about nuclear power in space squarely, now and in the future.