President Reagan's decision to press ahead with antisatellite weapons confronts military planners in the United States and the Soviet Union with new complications that will accelerate one part of the arms race.

Both superpowers, given the Reagan administration's opposition to a moratorium on antisatellite (ASAT) tests, will feel compelled to improve their capabilities to attack the opponent's satellites and defend their own.

Prodded by the sophisticated ASAT weapon Reagan said will be shot against a U.S. satellite this fall, the Soviet Union is likely to intensify work on a new generation of satellite killer. The one they have been testing and deploying since 1968 is little better than the ASAT weapons the United States deployed in the Pacific in the 1960s and then abandoned.

The new generation of ASAT weapons the United States has been developing have not been fully flight tested. There have been delays on the version that Reagan said will be shot at an object in space this fall. But this satellite killer, despite technical problems with it and the target vehicle, is far superior to the ASAT weapon the Soviets deployed, according to space specialists.

Military planners must assume the worst as they study what should be done to prepare to do battle in space. They must also recommend to their leaders how to make the ground links to satellites less vulnerable to attack.

Transcending these military preparations is the policy question of whether Washington and Moscow will continue to believe that it is in their mutual interest to allow satellites to continue whirling through space unimpeded, at least in peacetime.

In 1960, the Soviet Union was so incensed by U2 spy planes flying over its territory that it shot one down. A furious Nikita Khrushchev called off the scheduled summit meeting with President Dwight D. Eisenhower as part of his protest. But in the 25 years since, neither the Soviet Union nor the United States has made any move to stop the other's satellites from flying over its territory and snooping on its military establishment.

However, if both sides continue building more sophisticated versions of antisatellite weapons, it will be tempting to test them on the adversary's space vehicles.

The tests need not be any more lethal or provocative than the jamming, near misses and other ploys that the earthbound forces of both superpowers pull on each other. Such shadow boxing in space, where there are no humans to put the confrontation in perspective, is likely to be more nerve-wracking than that closer to the surface.

Space specialists talk about the "residual" capabilities of U.S. satellites already in space to harass Soviet satellites through jamming. It would be easy to build more harassment capability into U.S. satellites if the United States and Soviet Union decide to play chicken in space, as they did with warships in the Mediterranean before signing an agreement in 1972 to stop the game. Ships often bumped during those confrontations.

Navy officers were in touch with their commanders during those incidents at sea. There would be no human reporting on harassment in space. Specialists at radar consoles in the United States and Soviet Union would have to rely on green lines and dots to deduce what happenend to an errant satellite or one that suddenly went silent. Was it wrecked with a laser, jammed or did it just break? Should we respond in kind?

When U.S. and Soviet missile submarines first put to sea, the Pentagon conducted secret studies on how to keep them from interfering with each other or attracting killer submarines. One idea was to set up "exclusionary zones." U.S. subs would keep out of the Soviets' exclusionary zone and vice versa. But nothing of this kind was negotiated.

With Reagan moving ahead with antisatellite weapons and a "Star Wars" missile defense, there is fresh talk of establishing exclusionary zones in space to continue the open-skies arrangement -- this time under written rules.

Two arms-control specialists, Albert Wohlstetter and Brian Chow, proposed in the July 17 edition of The Wall Street Journal that "Self Defense Zones" be established in space where "each side would have the right to inspect, expel or otherwise render harmless any invaders should they exceed a safe number moving through these zones."

The possibility of sneak attacks against satellite links on the ground in the United States has only recently impelled the Air Force to disperse them.

"Before they starting putting their space stuff in Colorado," said one specialist, "all it would have taken was a suitcase full of explosives thrown over the fence at Sunnyvale [Calif., where most ground-links have been located] to knock us out of satellite business."

The Pentagon has commissioned a number of secret studies of ways to protect satellites, such as loading them with decoys which can be launched to confuse an attacker; parking them in deep space out of range of ASAT weapons until needed for low-altitude operations; using smoke screens to foil lasers; rocketing out of the orbital paths of hunter-killer ASATS, and shielding electronics and other vitals against nuclear radiation. The Soviets almost certainly are working on the same kinds of defenses.

The U.S.-Soviet race for dominance in space started with Sputnik in 1957. For years, however, both superpowers showed restraint, apparently because both agreed that space was more useful as an observation post than as a potential battleground. Reagan's determination to pursue both antisatellite weapons and a space-based missile defense seems likely to end that tacit agreement and initiate a new and expensive competition.