President Reagan's call for a leakproof missile defense will be taken seriously by the Soviet Union and force a reappraisal of Soviet offensive and defensive military programs, according to a wide spectrum of Kremlinologists.

Some of those interviewed said Soviet military leaders will conclude that the United States is moving toward a "first-strike" posture--the ability to fire nuclear weapons first and blunt retaliatory blows--while others saw no such destabilizing reactions.

"They're going to take it very seriously," said William G. Hyland, hitting the middle ground of opinion on how the Soviets will react to Reagan's recent call for "a comprehensive and intensive effort to define a long-term research and development program to begin to achieve our ultimate goal of eliminating the threat posed by strategic nuclear missiles."

Hyland is a Kremlinologist at the Carnegie Endowment for International Peace and formerly worked for the CIA and the National Security Council.

White House science adviser George A. Keyworth Jr. had put a "Star Wars" connotation on Reagan's effort by saying in an interview after the president's speech that "a very promising" concept involves generating laser beams on the ground and reflecting them from mirrors in space into attacking missiles.

"I suspect Soviet leader Yuri V. Andropov has called in his own high-energy people and asked them how come Reagan is so confident about being able to use light beams to destroy missiles," Hyland said.

The Soviets will "step up their own effort" in missile defense, Hyland predicted. "They'll suspect it's part of a new strategy. Andropov has said that the United States is going in the direction of first strike.

"But I think the Russians are going to be careful. I don't think they're going to break out of treaties and that kind of thing. They may fan the flames rhetorically," such as waging "a great propaganda campaign against putting weapons in outer space."

Vladimir Petrov, a native Russian who is professor of international affairs at George Washington University's Institute for Sino-Soviet Studies, said that Reagan's speeches have helped raise "the level of hostile reaction to an all-time high" in the Soviet Union, but that he does not foresee a direct U.S.-Soviet clash outside the propaganda arena.

Looking through the Soviet end of the telescope, Petrov said: "You remember when civil defense in the Soviet Union was interpreted here as preparations for the first strike? The Russians will say: 'The Americans are doing much more than we were planning to do. What is that but preparations for a first strike or at least conditioning the public that nuclear war is indeed possible?' "

Even so, he continued, "I don't see anything spectacular" in Soviet responses to Reagan's anti-ballistic missile proposals. "What bothers me a little bit with this new administration in Moscow is that they might go into higher risk-taking as far as our interests are concerned," he said.

Seweryn Bialer, director of Columbia University's Research Institute on International Change, also contended that Soviet military leaders must assume for planning purposes that Reagan is striving for a first-strike nuclear force that could launch weapons and then stop those launched in retaliation.

"Military men have to deal with capacities, not intentions," he said.

"That's complete nonsense," said Edward N. Luttwak of the contention that the Soviets will assume that Reagan's ABM drive is part of a new first-strike strategy.

"The Soviet marshals may say that, but they know it's not true," said Luttwak, a senior fellow at the Center for Strategic and International Studies.

Reagan would have kept his ABM ambitions secret and then suddenly deployed the defenses if he were going for first-strike capability, Luttwak reasoned. He predicted that the Soviets will step up efforts to steal U.S. technical secrets on missile defense.

Ray S. Cline, a former government intelligence executive and now a senior associate at the Center for Strategic and International Studies, agreed that the Soviets have no credible basis for believing Reagan is doing anything rash or destabilizing in missile defense. He predicted that the Soviet response "will not be much of anything but noise."

The Soviets have no reason to complain about the United States pursuing advanced ABM technologies, said Richard Pipes, formerly a Soviet specialist for Reagan at the National Security Council, "because they have been engaged in laser research for years."

Dismissing the dangers from Soviet counters to the Reagan ABM initiative, Pipes said that if the U.S. effort is not intensified, "one fine day we'll wake up, and they'll be ahead of us."

"What is really new about the president's initiative," said Raymond L. Garthoff, a Soviet specialist at the Brookings Institution, "is his decision to raise it to a major theme to generate substantial support in the United States for the idea" of trying to perfect a defense against nuclear missiles.

The Soviets "obviously see this as part of a bigger package" and find it "disquieting. The Soviets are going to look at this as having an offensive thrust in the sense we are, after all, getting launched at the same time on our offensive programs.

"In the short run, all it does is reconfirm the broad program they have been maintaining," Garthoff continued. "The key decisions are going to be made down the track." The Soviets first "will want to see how the debate develops in the United States" and will try to influence it by emphasizing the dangers of Reagan's course.

Marshall D. Shulman, special adviser on Soviet affairs to the secretary of state during the Carter administration and now director of the W. Averell Harriman Institute for advanced study of the Soviet Union at Columbia University, said Reagan's ABM initiative is "disturbing" to the Soviets because "it does raise questions about what the intentions of the administration are. They've been edgy about the space shuttle" because of its space warfare potential.

Presenting the ABM idea in part of a speech, rather than first consulting our allies, he said, also leads to a question in an already nervous Europe: "Does the United States really know what it's doing?" Reagan's speech "reinforces Europeans' impression that this administration is not serious about arms control," he said.

Marshall I. Goldman, professor of economics at Wellesley College and associate director of the Russian Research Center at Harvard University, said Reagan's ABM call could prove positive "if he follows up with substance and cools the rhetoric. It's an intriguing idea.

"There is an element of reality and objectivity in what he says" about relying on something other than mutual destruction to keep the United States and Soviet Union from firing missiles at each other, Goldman said.

But, he continued, if Reagan wraps the ABM initiative in the "evil empire" rhetoric of past speeches, the Soviets will accelerate military programs and try to reach an accommodation with China so more Soviet forces can be deployed on the European front.

"The Soviets have the thinnest waistlines in the world," Goldman said in dismissing the notion that they could not match U.S. military spending. "There always seems to be another notch in their belts. They have an enormous fear of America. They think that we can do anything we set out to do. All things considered, they're most worried about us beating them to the punch."

Leon Sloss, a former State Department executive on political and military affairs, and director of a Pentagon nuclear targeting study, said, "I've felt for a long time that we've undervalued defense but am distressed by the way it was sprung" by the president.

"I don't think the groundwork was well prepared with the allies or Congress. Somebody should have explored the possibility of talking to the Russians about this," he said.

Sloss rejected the idea that a missile defense must be perfect to be worth building. To have an effective missile defense, he added, "Clearly, arms control has to play a central role to constrain the offense."

He said one question that should be addressed as ABM research is accelerated is whether the Soviets would be likely to deploy a defense effective enough to stop the nuclear forces of Britain and France. Another is whether an effective U.S. missile defense would renew fears in West Germany that the United States was disengaging itself and allowing Europe to become the future battleground.

"The Soviets are in a much better position to deploy an extensive defense than we are. They've got up more of a head of steam. We don't have any fancy ways of penetrating an ABM. That program has been starved. The Soviets could deploy 1,000 interceptors by the end of the decade," Sloss said.

The first thing the Soviets will do, he predicted, is "try to raise opposition" to Reagan's ABM program "by playing on fears in this country and in Europe. The real question is after having been through the propaganda phase, will they feel tempted to do something about their own ballistic missile defense. Doctrinally, they have always been interested in defense.

"They may conclude we have given them the opening to go all out on ballistic missile defense. I don't think they'll do it all out, but creep up on the limits" of the existing ABM treaty.