A chilly new atmosphere has settled over East-West relations as the Soviet leadership seeks to prevent what it regards as the Polish disease from spreading to the rest of Eastern Europe.

With the crisis in Poland far from over, the Kremlin has evidently decided that detente with the West must take second place to the overriding priority of ensuring the stability and cohesion of the Soviet Bloc.

After an interval of some years, the air is again thick with calls for ideological vigilance and warnings of increased activity by antisocialist forces.

Soviet President Leonid Brezhnev last week used language reminiscent of the predetente era when he attacked "American imperialism" at a Kremlin banquet for President Babrak Karmal of Afghanistan. He accused both Democratic and Republican leaders in the United States, together with the news media, of launching "feverish military preparations and unbridled propaganda," which, he said, had reached an unprecedented level.

In Madrid, meanwhile, a deadlock has developed at a preparatory conference called to draft an agenda for a review of the five-year-old Helsinki agreement on security and cooperation in Europe. Soviet Bloc states are seeking to limit any examination of implementation of the agreements, particularly those passages relating to human rights.

But it has been East Germany where the sudden change of course has been most obvious. In an apparent attempt to stem the flow of West German visitors into the country, East Berlin announced that visitors would have to exchange considerably more Western currency for the soft East German currency and it followed this up with sharp attacks on Helmut Schmidt's newly reelected government in Bonn.

The unilateral currency move by East Germany took Western observers by surprise since it contrasted with what appeared to be a longstanding and carefully considered policy of improving relations with the West. As recently as six weeks ago, East German leader Erich Honecker was still speaking optimistically of "broad new horizons for relations with West Germany."

Other senior officials spoke of the good relationship with Bonn, which survived the strains of the Soviet invasion of Afghanistan, as "the only bright spot in the East-West spectrum."

It is widely assumed by Western analysts that the Soviets approved of the East Berlin move in advance, and possibly even instigated it. In a speech, Honecker used the unusual phrase "part of our coordinated policy" to describe the move.

East Berlin officials have tried to explain the new currency regulations in economic terms, arguing that the higher daily rate was designed to combat the black market in West German marks. But the most likely explanation lies in the East German leadership's desire to rebuild the country's ideological defenses to ensure against any repetition of the Polish crisis.

Of all East European countries, East Germany is superficially one of the most vulnerable to outside influence. Because of family ties, East Germany receives as many Western visitors as the rest of the Soviet Bloc combined. In addition, many East Germans were able to watch blow-by-blow coverage of the Polish strikes back in August and September on West German television.

An obvious fear for Soviet leaders is that East Germany might be left sandwiched between a liberalized communist system in Poland and a capitalist West Germany. The result would be idological isolation.

What is not clear, however, is whether the Kremlin's prime concern right now is to immunize other East European countries from the Polish virus or to eradicate the problem at its source -- in Poland itself.

Supported by the East Germans and the Czechoslovaks, the Soviet leaders have not disguised their deep reservations about some of the concessions made to the Polish workers and particularly the establishment of independent trade unions.

In a speech last week, East Germany's Honecker attacked what he called "antisocialist, counterrevolutionary forces" that he said had surfaced in Poland and were threatening the communist system.

He added: "Poland belongs inseparably to the world of socialism. Nobody can turn back the wheel of history. Together with our friends, we will make sure of that."

Meanwhile, a senior Czechoslovak official, Vasil Bilak, accused some of the leaders of Poland's new unions of seeking to weaken the Communist Party and paralyze the country.

Bilak was quoted by a Prague newspaper as saying: "Some people in Poland are making noises that they are not interested in politics and all they want to do is set up independent unions. But the practice shows that it is these very people who want to transform the alleged independent unions into a legal base of opposition activity and the main channel for continuing outside interference in Poland's internal affairs."

Taken together, these two warnings are ominously reminiscent of phrases used to justify the Soviet invasion of Czechoslovakia in 1968. There can be little doubt that the Soviet Union and its allies would be prepared to intervene directly in Poland should widespread disorders break out.

But there is no evidence to suggest that Moscow has lost confidence in the Polish leadership's ability to handle the crisis. Unlike the cases of Czechoslovakia in 1968 and Hungary in 1956, there has been no criticism of the Polish Communist Party so far.