Pinned down by the Afghanistan adventure in the east and Poland's crisis in the west, the Soviet Union has underscored its continued interest in the East-West dialogue by advancing a minimum starting point for its resumption.

The Soviet position -- it includes an offer to reestablish contacts with the United States "at all levels" and seductive measures to reduce tensions in Europe -- appear designed to salvage whatever can be salvaged from the policy of detente that the aging Soviet leadership adopted as its objective in world affairs a decade ago.

Yet these very leaders, with their growing assertiveness in foreign affairs that culminated in the Afghanistan invasion, have not only undermined detente but have also ushered in a climate in which the resumption of the arms race seems a likely prospect.

It is this turn of events that the Kremlin now appears determined to check through diplomatic means. The objective is to counter a truculent new American mood and prevent the Reagan administration from embarking on a new spurt in strategic weapons building that this economically troubled giant would undoubetly match -- but only with enormous sacrifices.

As no Soviet leader before him, President Leonid Brezhnev established the Soviet Union as a superbly armed state and a world power broker with the United States. But the events of the past 14 months, from the moment Soviet troops entered Afghanistan, to the unpredictable process still under way in Poland, have threatened to undo many of those gains.

Militarily more potent than at any time in its history, Russia today faces world fears and outright condemnation from many capitals that it is unable to live in peace with its neighbors and lacks the interior restraints to keep from meddling with the power balance thousands of miles from home. It has been condemned by an overwhelming majority of the United Nations and Islamic countries for the invasion of Afghanistan, and its possible intervention in Poland has sent tremors throughout Europe, including its own Eastern satellites.

Now, Brezhnev and his Politburo are bidding openly for a way to ease the Kremlin's predicament.

These complex, interlocking factors spurred Brezhnev last week to open the Communist Party's 26th Congress with an offer to meet President Reagan at a summit and to bolster that with a package of disarmament initiatives calculated to catch the eye of Western European leaders as well.

Monday's promotion of American affairs specialist Georgy Arbatov to full voting status in the Central Committee was another sign of Moscow's interest in bilateral dialogue. Arbatov, thought to have access to Brezhnev, is a seasoned ideologue who favors improved ties with the United States. As head of the Institute of the U.S.A. and Canada, a Central Committee think tank, Arbatov is a familiar face in Soviet public life. He also has forged impressive contacts with U.S. politicians and policy advisers.

So far, the cautions Western response has irritated Moscow, as Kremlin spokesman Leonid Zamyatin made clear in a series of press conferences he held during the Congress. But the plain fact is that Western diplomats seeking substance beneath the symbol that Brezhnev's gambit represents have been hard put to find anything new in his proposals.

The principal concrete initatives that have drawn the most study from foreign analysts and been most heavily touted by Soviet journalists and other party sources are Brezhnev's renewed call for a freeze on deploying new medium-range nuclear missiles in Europe pending talks on a permanent moratorium and a reciprocal expansion of the zone for notifying foreign governments of major troop maneuvers.

Brezhnev first made the freeze proposal on theater nuclear forces in October 1979, before NATO voted to deploy advanced Pershing rockets and Cruise missiles in the face of a Soviet deployment of advanced, multiwarhead SS20s in western Russia targeted on West Europe. The zone of expanded "confidence building measures," which now covers Western Europe, parts of Turkey and most of the Soviet European frontier 155 miles deep, first was proposed by French President Valery Giscard d'Estaing.

On Monday, spokesman Zamyatin criticized the West Germans, who have indicated they see little new in the arms proposal. "It is a freeze both in number and in quality, and this is a new factor," Zamyatin insisted. "This would freeze the modernization process."

Well-informed Western analysts agree that the emphasis on freezing "quality" is a distinct new ingredient not previously publicly stressed by Moscow. A qualitative ban would stop replacement of older missiles of shorter range and less accuracy with new missiles, a major goal of general arms limitation talks.

However, the sources say, the Soviets have already deployed more than 150 SS20 missiles and could stop short of replacing the older SS4s and SS5s and still retain supremacy in this area so long as NATO suspends its plan to deploy the new Pershings and Cruises.

Brezhnev offered to extend the zone of confidence building measures all the way to the Urals, effectively taking in the bulk of Soviet ground units, but did not specify what reciprocal Western expansion the Soviets may want. There has been no further exploration of this through diplomatic channels here. But Western military sources believe the Soviet goal is to include part of the United States as the quid pro quo, since Western Europe is already within the existing zone.

The other Brezhnev proposals include willingness "to continue without delay" all bilateral arms negotiations, willingness to participate in a separate settlement of Afghanistan or include it in a general Persian Gulf security conference, bilateral talks to limit deployment of giant missile-firing submarines and a new call for a Middle East peace conference.

Any sign of positive reaction from Washington or Western Europe to these proposals would encourage Moscow as it seeks ways to ease its Afghan and Polish troubles. For this reason, Western diplomats here have been extremely cautious in talking about them in the firm belief Moscow would use any East-West opening as leverage in its test of wills, especially with Pakistan, to gain acceptance of the Afghan regime its troops keep in power.

At the same time, a number of West European diplomats are increasingly unhappy with the Reagan administration's decision to step up U.S. involvement in El Salvador. In their eyes, this only eases Moscow's diplomatic predicament over Afghanistan.

Meanwhile, the Polish crisis offers major internal and external problems for the Kremlin. Emergence of the independent unions has narrowed party authority in ways that worry East Bloc capitals, whose economies are lagging in the face of rising expectations. Yesterday's meeting here of Soviet and Polish leaders reaffirmed that the threat of an eventual direct intervention in Poland has not faded. The two countries' top officials jointly made clear that the "Brezhnev doctrine" of intervention to preserve a communist government in power is still very much alive.

As the Congress showed, Moscow has more than enough to occupy itself in the next five years simply trying to meet its own reduced economic expansion plans.