Superpower space ties. Despite the US-Soviet stalemate over an arms accord, one idea discussed at Reykjavik has borne fruit: joint space research. American and Soviet scientists have now agreed to study the sun.

American and Soviet space officials are developing a new program for space cooperation. It's one of the less publicized fruits of the Iceland summit.

An agreement in principle, which was worked out there, has opened the way for specific agreements on projects. American and Soviet space officials, meeting in Padua, Italy, late last week, said the two countries will cooperate in a major international study of Earth-sun interaction. They're also talking seriously about coordinated surveys of Mars.

``I think you can be quite optimistic about it [US-Soviet space cooperation],'' says Robert Parks, deputy director of NASA's Jet Propulsion Laboratory.

Last September, JPL director Lew Allen led an American delegation to Moscow to explore cooperation with Soviet officials. In late October, Raold Sagdeev, director of the Soviet Institute of Space Research, held post-summit discussions in Washington. NASA officials are saying little about the discussions. But, Mr. Parks notes, it's obvious that ``they're doing some very delicate negotiations.''

The International Solar-Terrestrial Physics (ISTP) program, which the Soviets will now join, ranks high on the list of major missions recommended by the Space Science Board of the US National Academy of Sciences. A dozen satellites will study solar radiation and the solar wind of charged particles and their interaction with our planet in the 1990s. The United States will contribute three satellites.

The European Space Agency (ESA), an ISTP member, is to orbit four to five probes. Japan, also a member, is to orbit one to two. The Soviet Union will contribute two or three craft.

Mr. Sagdeev and Burton I. Edelson, NASA associate administrator for Space Science and Applications, openly discussed the project during the recent meeting of the Inter-Agency Consultation Group (IACG) in Padua. The IACG was formed in 1981 to coordinate Comet Halley missions. It was ``so successful,'' Dr. Edelson says, ``we have decided to continue it.'' Both sides consider it a useful vehicle for ongoing East-West joint efforts.

For their part, the Soviets are continuing the open approach to international space research which characterized the Halley cooperation. Britain and France have concluded individual agreements to join in major projects with the Soviets. British scientists, among other things, now are integrating with the mission team for the Soviet Phobos project that will explore one of the moons of Mars. It's due to launch next year. Meanwhile, France will again send an astronaut to a Soviet space station within a couple of years. This will give France an opportunity to test equipment that would later be used in ESA's planned Hermes space shuttle.

Many space scientists expect some sort of American-Soviet Mars research as well.

After his Washington visit, Sagdeev said it's premature to plan manned Mars missions. But it would be quite feasible to coordinate the Soviet Phobos and a second Mars mission, called Vesta, with NASA's Mars Observer program. The latter will probably launch a spacecraft in 1992 to orbit Mars. Sagdeev pointed out that this initial cooperation could lead to more ambitious joint projects.

Dr. Edelson agrees that such coordination makes sense. He says he hopes that ``IACG will be able to play some coordinating role.''

Mars scientists at JPL would welcome an opportunity to cooperate with Soviet colleagues. ``We see a lot of potential to just try to cooperate in ways that would maximize the return of those two missions,'' Parks says.

At this point, the space science negotiations seem to be progressing in their own right in spite of the divisive issue of American Strategic Defense Initiative research which hampers arms control talks. Sagdeev has indicated that he would like to keep it that way. He told the Associated Press in Padua: ``A peaceful space exploration like this [ISTP] should not be made hostage to differences over the Defense Initiative or any other military enterprise.'' He did add cautiously, ``I would not insist on legal linkage between the two issues, but I certainly would not deny that there is a linkage factor.''

While it's difficult to interpret just what this means, Parks calls Sagdeev's comments ``a positive sign.''