By deciding to halt Soviet medium-range missile deployment for six months, Mikhail Gorbachev has chosen a timetable that gives the Soviet Union important tactical advantages beyond the more evident public relations gains, leading Kremlinologists said yesterday.

The unilateral freeze, experts on the Soviet Union said, appears to be intended to placate nuclear arms opponents in Western and Eastern Europe, buy Moscow time to redirect its medium-term missile strategy and give the new Soviet leader a positive image before a possible summit with President Reagan.

In each case, they view the Soviets' choice of Nov. 1 as the expiration date for the freeze as key. "The date is tactical," says Arnold Horelick, a Sovietogist at UCLA and the Rand Corp.

The Dutch government's decision on whether to deploy 48 cruise missiles is scheduled for the beginning of November. Last June, the Dutch government sparked controversy in NATO by announcing that it would cancel its planned deployment of medium-range missiles if the Soviets would freeze their arsenal of SS20s, which at that time totaled 378 missiles.

By postponing the deployment of cruise missiles, the Dutch government became the first NATO country not to meet the alliance deployment timetable.

Since then, SS20 deployments are estimated to have climbed to 414.

Dutch Foreign Minister Hans van den Broeck, due to arrive in Moscow today, is expected to discuss the deployment issue with key Soviet officials. He is scheduled to meet Andrei Gromyko, his Soviet counterpart, on Wednesday. "The Soviets clearly want to use these six months to maximize their influence on the Dutch," Horelick said.

Critics of the moratorium think that Moscow will use the next six months to complete construction of SS20s already under way, effectively closing out a cycle of deployment that they think is nearly finished.

In addition, they say, the Soviet government simultaneously could complete plans for the modernization of its missile system, which Soviet specialists in the U.S. Defense Department think is well under way. Western analysts expect ratification of the modernization when the Soviet Communist Party Congress convenes to discuss the five-year defense plan soon after the missile freeze expires.

"It looks as if the SS20 deployment sites are near to completion anyway," said Helmut Sonnenfeldt of the Brookings Institution. "All conceivable SS20 targets are more than adequately covered." Other Kremlinologists agree that the current arsenal of 414 SS20s, each carrying three warheads, covers the 1,200 assumed targets.

Raymond Garthoff, also of Brookings, pointed out that if the Soviet government follows the pattern set in its March 1982 moratorium, it will use the freeze time to "seal the cement" on SS20 sites already started.

Other close watchers of Moscow said that in announcing the moratorium, Gorbachev has begun an image-building campaign that is timed to climax in six months -- at about the time the Soviet leader would be meeting with President Reagan. Although the date and place of the proposed summit between the two remain open, both the United States and the Soviets have agreed to the meeting in principle. And signals from the West suggest that it will take place next fall.

"This moratorium is not a one-dimensional trick," said Dmitri Simes, a Soviet affairs expert at the Carnegie Endowment for International Peace. "Gorbachev is trying to position himself for an encounter with President Reagan."

In that regard, Simes explained, the moratorium is a gesture to give the Soviets a conciliatory image in the eyes of the Western European public, at a time when governments and peace movements in Western Europe will be trying to determine who is approaching the arms talks in Geneva most positively. Gorbachev, said Simes, has begun a string of attempts to look "reasonable" and "flexible."

Most analysts agree that the freeze is only the beginning of Gorbachev's initiatives in the battle for the attention of the public in Western Europe and in the United States.

Seweryn Bialer, a Kremlinologist who has just returned from a visit to Moscow, said, "We should now expect a policy from the Soviet Union that, in regard to the arms race, will be more imaginative and more active. The Gorbachev freeze is the beginning of it."

The Soviet freeze seems designed to respond to the restlessness about Soviet deployments of medium-range missiles in East Germany and Czechoslovakia.

In addition, as Gorbachev's first major policy initiative, it gives him an image of approaching the United States positively. The Gorbachev announcement was covered extensively in the Soviet press, and it included the first public Soviet mention of the proposed summit between Gorbachev and Reagan.