Next month, the Soviets are scheduled to launch two space probes to Phobos, one of Mars' two asteroid-like moonlets. The probes, which will hover just over the moon, will analyze its composition by using lasers and other instruments and by sending landers to the surface.

The Phobos probes are the first in a series of Soviet unmanned Mars expeditions. Future Soviet plans include mobile surface probes, or rovers, that will collect and study soil samples from a wide area on the planet itself, and small rockets that will carry some samples back to Earth for study later."During the coming decade, humanity will learn more about Mars," wrote former astronaut Sally Ride in a 1987 NASA report, "but it will largely be the result of ambitious Soviet, not American, programs." However, the Soviet Mars program may also provide a unique opportunity for NASA to revitalize its struggling space science program through more international cooperation.

As a part of a U.S.-Soviet cooperative space agreement signed in Moscow last year, for example, the Soviets will use NASA's Deep Space Network to help track and communicate with the Phobos probes. In return, U.S. scientists will gain direct access to the Soviet's data. But the United States has limited its role in the probes.

"The basic trouble is that when you're flying hardware on their spacecraft, they can presumably take your hardware apart and understand it," says Samuel Keller, NASA's deputy associate administrator of the office of Space Science and Application. The technology-transfer issue "is something we can live with," he says. "But you have to be very careful and methodical."

Space cooperation was on the agenda at the Moscow summit, but no new joint missions were planned. Nevertheless, as NASA's budget continues to tighten, cooperation may become an economic necessity.

At one time the United States was pre-eminent in the unmanned exploration of the planets, but NASA has not launched a new interplanetary space mission in 10 years. Budget cuts forced NASA to cancel plans of its own probe to Halley's Comet, and other programs have been repeatedly delayed. Several important space probes are stuck without a launcher until the space shuttle resumes operation later this year, but even then, the huge backlog of commercial and military payloads may restrict the number of flights NASA can reserve for scientific missions.

So NASA is using data from its 1975 Viking probes to help the Soviets identify possible landing sites for their rovers and sample-return missions, and the agency's 1992 Mars Observer spacecraft, currently its only scheduled Mars mission, may act as a relay satellite for a Soviet rover mission in 1994.

The issue, then, is not whether to cooperate, but how much, as Soviet space probes continue to grow in sophistication. Complicated cooperative missions involving Mars rovers or sample-return flights would allow the United States to participate in space exploration and science projects at half the cost, but they could expose sensitive technological information.

Cooperation, Keller says, "is technically feasible. It's matter of whether or not the political leaders want to do it that way."