The Reagan administration's Strategic Defense Initiative could damage international stability, help encourage a superpower first-strike strategy and lead to a weakening of military ties to the European allies, according to a leading defense think tank here.

In its yearly Strategic Survey, scheduled for release Friday, the International Institute for Strategic Studies said the administration's space-based antimissile defense program, known as "Star Wars," "promises to be the most controversial issue of the coming year."

While this year's survey described 1984 as a time when East-West relations largely "marked time," it said that "neither the course of events in 1984 nor the exchanges in the early months of 1985 raises hopes" that the time was used fruitfully.

Although the Soviet Union appears to have set aside its insistence that western cruise and Pershing II missiles must be removed from Europe before arms control negotiations could proceed, the study said, "considerably more flexibility will be called for" from the Soviets "if there is to be any significant prospect of avoiding the impasse of 1983," when the Soviets walked out of talks.

The report predicts an increase in "the vigor and forthrightness with which Soviet policy is presented" under the new leadership of Mikhail Gorbachev, but notes that "there are as yet no signs that there will be much change in Soviet foreign policy."

Additionally, it said, the Soviets are likely to run into increasing problems of "alliance management" in Eastern Europe.

With no signs that either superpower intends to change policy to "bridge the gap" between them, the institute noted that the Star Wars proposal had opened "a controversy which will run for many years."

The program "goes to the fundamentals of existing strategic policies and postures, because strategic defenses conflict with the logic of assured mutual vulnerability -- the foundation of stability between the superpowers for over 20 years."

Noting that the Star Wars debate would likely cloud ongoing discussions about the defense buildup in the United States, and that "a substantial body of scientific opinion disputes the feasibility of the SDI on technical grounds," the institute said that its entry into the strategic mix necessitated a "reexamination of the foundations" of nuclear defense and deterrence.

Such a reexamination "will call for a major intellectual effort (and much more clarity of thought than has yet been shown) on the part of governments and opinion leaders in East and West."

Echoing concerns expressed by a number of Western European governments, the survey said that "even if strategic defenses were to prove feasible, they could damage stability rather than strengthen it. During the transition period" between deterrence and antimissile defense, "should one side have strategic defenses which the other does not, a first-strike strategy becomes more thinkable."

In addition, it said, "defenses against ballistic missiles may encourage the further development of other means of strategic attack."

Finally, "if strategic defenses were to be as effective as President Reagan hopes and lead eventually to the elimination of nuclear weapons, it is not at all certain that western interests as a whole would be served by having to rely exclusively on conventional forces to protect those interests." The nuclear defense system, the survey said, could lead to a Soviet buildup of conventional forces that would threaten Western Europe and East Asia at a time when the United States might be less willing to help defend them.

It said that little progress had been made last year in resolving regional security problems, and little was expected this year. At the same time, it noted that "the erosion of superpower ability to control regional conflicts has continued," although "many of the more significant regional powers seem to be prepared to play a more active role in attempting to improve security and restore peace."