After years of fire-and-brimstone rhetoric, the Soviets gradually have climbed down from their initial positions on limiting medium-range nuclear weapons.

Their latest offer--described as a "starting one" by knowledgeable Soviet sources--suggests that the Soviets would make additional concessions to prevent the deployment of new U.S. missiles in Western Europe. Thus, one can argue that the Reagan administration has been successful with its unyielding attitude in talks in Geneva on the missiles.

Yet, the Soviets never have been known to be willing to pay for something as long as they expected to obtain it for free some day. At the same time, they are known to have pursued with single-minded persistence security interests that they regard as absolutely essential. The question now is whether Washington can properly assess where the first attitude stops and the second begins.

It is in this context, according to Soviet and western sources here, that one should view a series of recent Soviet proposals ranging from Soviet leader Yuri Andropov's interest in a meeting with President Reagan to the Warsaw Pact leaders' offer to negotiate a nonaggression treaty with the North Atlantic Treaty Organization.

Despite optimistic statements in Washington, this country has entered the new year with a distinct feeling that time is running out slowly for an agreement with the Americans in Geneva.

The two superpowers are involved in two separate arms negotiations in Geneva. One deals with the strategic weapons, or the largest land- and sea-based missiles capable of hitting targets 5,000 or more miles away. The other deals with smaller, or medium-range missiles, deployed or scheduled to be stationed in the European theater. Both sets of the talks are regarded here as deadlocked.

The medium-range missile talks have acquired a greater urgency here in the view of the planned deployment of 464 new U.S. cruise and 108 Pershing II missiles in Western Europe at the end of the year. The heart of the problem is the deployment in West Germany of all the Pershing II missiles.

While the United States contends that Pershing II is a medium-range weapon needed to offset Moscow's force of similar SS20 missiles, the Soviets insist that the Pershings constitute a strategic first-strike force capable of obliterating military and command and control points throughout European Russia.

Well-informed sources here say that the Soviet military would oppose any acceptance of Pershing II missiles in West Germany. This presumably means that the Soviets have resigned themselves to, at a minimum, NATO's deployment of cruise missiles. But cruise is not a first-strike weapon like the Pershing, which could reach Soviet targets within five minutes.

Of all the various Soviet arms-control proposals, the most important was advanced by Andropov on Dec. 21.

The first part of his offer deals with strategic arms and was based on the 1972 Strategic Arms Limitation Talks agreement in which the United States and the Soviet Union accepted the principle of strategic parity. Andropov suggested that both countries cut by one quarter their strategic arsenals. He also proposed agreed cuts in the number of warheads, something not covered by that SALT I agreement.

The second part of the offer was to reduce the number of Soviet medium-range missiles to match the combined deterrent arsenals of France and Britain. This would be done if NATO abandons its planned deployment of medium-range missiles.

Well-informed sources here said the offer of sharp cuts in the number of Soviet medium-range weapons was made to create some "movement" in the Geneva talks. The proposal, in practice, cut almost in half the previous Soviet offer to freeze the number of their medium-range missiles at 300 if the United States would not deploy its cruises and Pershings.

Moscow repeatedly has asserted that in the field of strategic weapons it would not permit Washington to gain advantage and that it would match any new U.S. weapons program. There is no substantive proof that the Soviets have the technological and other resources to do so, but there also is no proof that they do not have them. Officials here point out that in the past the Americans have underestimated Moscow's ability to muster its resources, and they assert that the same miscalculation could be made again.

The main Soviet diplomatic and propaganda objective at the moment is to push the Reagan administration from its "zero option" proposal at the medium-range talks in Geneva. Under this proposal, the deployment plan for the new U.S. missiles would be scrapped in exchange for the dismantling by the Soviets of all their medium-range nuclear forces in the European theater.

One important aspect of the peace initiative is to persuade Western public opinion to resist the deployment of the new American missiles. Since the decision was made three years ago, the new missiles have become a political liability in several key Western European countries where they are to be based. A mass antinuclear movement has emerged in Britain, the Netherlands, Belgium and West Germany, and it has acquired influence within the opposition parties in those areas.

Capitalizing on this development, the Soviets are continuing to play Europe against the United States in the hope that the existing divisions would help foil the NATO decision or, at a minimum, force Washington to abandon its "zero option."

Moscow's appeal also is addressed to the Americans. The Soviets have been heartened by the specter of an antinuclear movement sweeping through the United States, with referendums on a nuclear freeze and the antinuclear activities of prominent church and political leaders.

Looking from Moscow, the peace offensive seemed to have put many western governments on the defensive. This was made clear by cautious and noncommital reaction to last Wednesday's Warsaw Pact political declaration that restated virtually every Soviet peace initiative advanced in the past 10 years.

Western diplomats here believe, and some Soviet sources agree, that little movement is to be expected at the Geneva talks before the situation in West Germany becomes clearer. The proposed deployment is likely to become one of the main issues in West German elections on March 6 and important elements in the opposition Social Democratic Party seem to be edging toward positions against the new missiles.

While playing to the West European and American audiences, the Soviets are making it clear that they would like to reestablish a direct political dialogue with the Reagan administration. Andropov made that explicit in his answers to questions cabled by a U.S. reporter.

In proposing to cut to 162 the number of Soviet medium-range missiles in Europe, Andropov is said to have made the gesture of conciliation and opened the way to a compromise. Yet a compromise is unlikely if relations between the superpowers remain frosty.

There is no indication of what Andropov is willing to pay in Poland, Afghanistan or elswhere to achieve an improvement in relations.