Soviet President Leonid Brezhnev's speech in East Berlin last Saturday, in which he combined conciliatory gestures with threats in an effort to forestall deployment of new U.S. medium-range atomic missiles in Europe, is being seen in allied capitals as a skillful attempt to stir up public opinion and enlist the sympathies of Western Europe's sizable left wing as a way to stop governments from accepting these weapons on their soil.

"that is very definitely the case," says A.B.N. Frinking, spokesman of the parliamentary defense committee in the Netherlands. "we are not blind. We see what is going on," he says of Brezhnev's tactics. Nevertheless, he adds, "the people in Holland want to stop the action-reaction cycle of the arms race so we shouldn't say it is an offer that is not worthwhile until we have more facts."

The question of deploying some 572 new U.S.-built Cruise missiles and Pershing Ii missiles in Western Europe to balance new Soviet SS20 missiles already in place is one of the most significant and politically sensitive issues to confront the North Atlantic Alliance in many years. It has now been made more so by the direct involvement of the Soviet leader. This could drive a wedge between the United States and some of its European allies.

While U.S. officials tend to treat the Brezhnev remarks as mostly propaganda, Europeans, living closer to Soviet power and influence, are scrutinizing them intensely for clues to the future of detente on the continent.sc

Though NATO ministers have already indicated they are likely to authorize going ahead with deployment at the alliance's forthcoming December meeting, that approval will then have to be ratified by parliaments back home.

Diplomats and experienced political observers in some countries where those missiles would be stationed acknowledge, however, that the Kremlin leader's proposals and threats could have an effect on public opinion and on parliamentary approval.

At stake, therefore, are not only questions of modernizing NATO nuclear weapons and the European balance of power, but also cohesion of the alliance on a fundamental question of future defense policy, relations between Western Europe and the Soviet Union, and the atmosphere surrounding future nuclear arms limitations talks and East-West troop reduction talks.

The issue is so sensitive in the Netherlands, say several sources, that the fragile coalition government there could possibly fall if it backs the deployment plan. this, in turn, could influence support for the deployment plan in neighboring Belgium. And, if Belgium waivers, that leaves only West Germany. Bonn has said repeatedly that it will not be the only West European nonnuclear country to provide bases for these new weapons.

At a seminar of the Atlantic Institute in Paris last week, Klaas de Vries, chairman of the defense committee of the Dutch Parliament, said that his country would want to know Belgian intentions before committing itself.

Thus, the issue is probably more fragile than the expected NATO endorsement reflects, and Brezhnev obviously senses that.

The U.S.-NATO plan is to begin, within the next few years, emplacing 108 new pershing land -- based missiles to supplant a similar number of existing shorter range pershings. In addition, about 464 ground -- launched Cruise missiles would also be deployed.

The United States has had atomic weapons in Western Europe for 30 years -- some 9,000 of them are still here, sources say. But the crucial difference -- to the Kremlin as well as the West Europeans -- is that these new missile, for the first time, would be able to fly more than 1,000 miles and thus strike targets in the Western Soviet Union from their European bases.

The missiles would be on U.S. bases, with the Pershings stationed primarily in West Germany and Cruise missiles here as well an in England, the Netherlands, Belgium and possibly Italy. Authoritative sources say they would also be exclusively under U.S. control rather than joint control so as not to force the allies to have a finger on the nuclear trigger aimed at the Soviet Union.

The number of missiles reportedly was arrived at by calculating that the Soviets, who now have more than 120 of the new and mobile SS20 missiles deployed, would eventually have about 200 of these, each armed with three warheads for a total of about 600 individual weapons.

The alliance has nothing to match those Soviet weapons at this point and it is because of the desire to plug that real, or perceived, gap in the West's ability to deter attack at any level and to resist severe political pressure that NATO wants the new missiles.

In his speech, Brezhnev first captured attention by a unilateral pledge to withdraw up to 20,000 Soviet troops from the roughly 400,000 believed stationed in East Germany and 1,000 of the 7,000 tanks there as a gesture of "goodwill and detente."

Then he said the Kremlin was also ready to negotiate reduction of its medium -- range rocket force based in Europe, but only if the West refrained from deploying new weapons. If there was no restraint, he threatened stern Soviet countermeasures.

Officials throughout NATO have reacted with cautious interest to Brezhnev's proposals, seeing some positive elements in them but also seeing attempts to confuse the Western public.

The allied political strategy to get the plan approved has always revolved around finding a partner for West Germany. Britain, whose Conservative government is expected to support the deployment plan, in Bonn's eyes does not count as a partner because it is already a nuclear power.

The effort to gain Dutch backing centers around what is called a "switch" plan in which it is hoped Dutch reservations can be overcome by removing some older U.s. nuclear bombs, artillery and antiaircraft weapons and replacing the missions to be carried out by these forces with the new missiles.

Belgium remains the key. Foreign Minister Henri Simonet is widely viewed as strongly disposed to back the NATO deployment plan. The Belgians are seen as not nearly as sensitive as the Dutch on such questions and as more pragmatic on security issues, like the French. Indeed, some Belgian officials privately say their country is simply "passive" about a lot of things except taxation.

For the West Germans, the conciliatory portions of Brezhnev's speech were seen as a boost to getting SALT II ratified in the United States. Without SALT II, there would be no SALT III and therefore no forum to discuss the European arms control portion of the NATO plan.

The Kremlin has put considerable pressure on Bonn, which highly values its realtionship with the Soviets and which has an active left wing in its ruling Social Democratic Party.

Egon Bahr, a leading figure in the Social Democratic Party here who has close ties to the Soviets and was a strong opponent of U.S. neutron bomb deployment plans, called on Moscow to stop production of the SS20 and said "the way in which the Russians publicly criticize Western plans, which are simply answers to Soviet actions, do not help very much."

In an editorial this week, the influential center-left French newspaper Le Monde also pointed out that the "new phase in the arms race in Europe was not only the fault of NATO militarists but rather more the fault of the Russians, who ensured a Western response by considerably reinforcing their panoply of theater nuclear arms in recent years."