The Soviet Union has refrained from testing its antisatellite weaponry for almost a year, raising the Carter administration's hopes that the military space race can be slowed through negotiations scheduled to resume in Vienna on Monday.

Defense Secretary Harold Brown told The Washington Post that it "may be feasible to damp down" the antisatellite developments that threaten to push war into outer space.

"Everybody would be better off," Brown added. The Soviet marotorium on antisatellite tests-in effect since last May 19-may mean the Kremlin has come to that same conclusion.

Administration officials freely acknowledged yesterday that they do not know why the Soviets suspended their huntre-killer exercises with satellites in space but are hoping for the best.

One administration idea is to try to negotiate a one-year ban on antisatellite testing, although many other options will be explored in this third round of space warfare talks.

"I don't know if you could stop it," Brown said of the antisatellite efforts of the two superpowers, "but you can damp it down. That's what we're trying to do.

"As usual," the defense secretary continued, "you wind up in a conflict between wanting to damp it down and being afraid that the other side will go ahead."

Pentagon space weapon specialists said negotiators are faced with a "bird-in-the-hand versus bird-in-the-bush" situation.

This time the Soviets have the bird in hand because they have tested-in 17 different exercise s-satellites designed to intercept and destroy other satellites in space.

In contrast, the United States is still working on what the Pentagon considers a far superior satellite killer-one that homes in on the heat of the enemy satellite and flies right into it. But this "flying tomato can" being developed by the Vought Corp. is not expected to be flight tested before 1980.

President Carter, in a secret decision paper circulated last year, said he cannot accept "asymmetry" in space weapons by allowing the Soviet Union to take a commanding lead in that field over the United States.

Some Pentagon and Central Intelligence Agency specialists contend there cannot be symmetry until the United States actually flight tests its newest antisatellite weapon, even if everyon agrees U.S.% technology is superior to the Soviet Union's.

A counterargument is that this is the time to nip the antisatellite effort by both sides, otherwise it will keep escalating to more and more lethal space weapons, as he has been the case with missiles.

President Ford had approved the development, flight testing and deployment of the "flying tomato can." President Carter, sources said, at first decided to stop short of flight testing but then relented last spring and told the Pentagon to plan on at least testing its new antisatellite weapon.

The Soviet antisatellite program has involved launching a target satellite in space and then sending up a "hunter-killer" satellite. Once the hunter-killer gets near the target, the former explodes-apparently relying on explosive force or shrapnel for the kill.

However, so far the Soviets have tested killer satellites that are too low to hit anything but low-flying U.S. spy satellites and old-model navigation satellites.

Specialists credit the Soviet killer satellites with an altitude of about 120 miles-far below the 23,000-mile zone where military communication and warning satellites hang in space.

Still, the threat of having the low-flying U.S. spy satellites blinded in a period of tension is a worrisome one, especially since it is becoming increasingly difficult to keep track of Soviet military activities in the old ways. The loss of CIA monitoring gear in Iran is the latest of such reduced capability from ground stations.

Brown has warned repeatedly that the United States will not sit back and allow the Soviets to take a commanding lead in space warfare weaponry. He believes the United States could win such a race.

"If we're willing to spend the money," Brown told The Post, "we've got the technology to win. But the point" of both sides engaging in such a race "is much less clear to me."

Asked about the prospects of negotiating a one-year freeze on antisatellite activities, Brown replied:

"That may be feasible because neither side has tested during the last year."

The latest Soviet antisatellite flight involved sending Cosmos 1009 against Cosmos 967, the target satellite, on May 19, 1978. In 1977, the Soviets were much more active-launching three target satellites and four hunter-killers.

The United States actually got ahead of the Soviets in the 1960s by deploying an antisatellite, missile-war-head combination on Kwajalein Atoll in the Western Pacific. It also pursued on paper a secret Air Force program called SAINT (for satellite inspection).