The Soviet Union has mounted a campaign of heavy pressure on Turkey with a flurry of propaganda assaults on its military government and open expressions of diplomatic support for the new Socialist government of Greece in its dispute with Turkey.

After virtually avoiding criticism of the Turkish military takeover 16 months ago, the Soviet news media have used the strongest language during the past week to denounce what it calls the Turkish junta's "violation of human rights" and "bestial" treatment of political prisoners.

The sudden shift in attitude toward a sensitive neighbor was seen in part as an effort to counter the Western outcry that followed the imposition of military rule in Poland.

But the Soviets also have abandoned their traditionally evenhanded stance toward Greek-Turkish disputes to take a distinctly pro-Greek position.

Soviet sources privately conceded that the shift in Turkish policy was designed to provide support for the new Socialist government of Greek Premier Andreas Papandreou and sustain his independence and assertiveness in foreign policy.

According to the sources, the Reagan administration is seen here to be using Turkey as a "lever" to keep Papandreou from implementing his electoral pledges to negotiate a gradual phase-out of U.S. military installations in Greece and take the country out of the North Atlantic Treaty Organization.

The Kremlin has been looking with satisfaction as Papandreou broke ranks with NATO allies on the question of sanctions against the Soviet Union and Poland over Poland's imposition of martial law. Papandreou also has hinted that he may block procedures to bring Spain into NATO. His demand that NATO should guarantee Greece's borders against an attack by Turkey, also a NATO member, caused an alliance defense ministers' meeting in December to end without a communique, for the first time in the alliance's 33 years.

A series of incidents involving alleged Turkish naval violations of Greek territorial waters in recent weeks has produced a new exchange of insults between Athens and Ankara over the disputed Aegean Sea waters and their rival claims to the continental shelf.

While a member of Greece's opposition, an intensely nationalistic Papandreou had called on the Greek armed forces to take "dynamic action" against a Turkish survey ship prospecting for oil in Aegean areas claimed by Greece. Six years ago the two countries, their relations already disrupted by the Turkish invasion of Cyprus, came to the brink of war over the issues.

Since taking office last October, however, Papandreou has moderated his pronouncements on the question of the continental shelf.

According to diplomatic observers, the Soviets are believed to fear that Papandreou's inability to deal with Turkish pressures could force him into a political dialogue under the auspices of NATO and blunt his independent policies.

The official Soviet news agency Tass asserted last week that the "real threat to Greece" comes from Turkey. The Communist Party newspaper Pravda at the same time endorsed the Greek position on the Aegean issues by saying that the problem should be resolved "according to the principles of international law and established practice."

Under a 1923 pact, Greece gained control over more than 3,000 Aegean islands with the exception of Imvros and Tenedos, which guard the entrance to the Dardanelles. The Turks for decades did not challenge this until the early 1970s, when prospects arose of oil fields in the Aegean.

Should Greece extend its present six-mile territorial limit to 12 miles--as reportedly has been discussed in Athens--the Aegean would practically become a Greek lake, with expanded territories around the many islands.

The Turks, who have adamantly opposed any extension of territorial limits on grounds that it would severely hamper their lines of communications, have argued that the Aegean is a special case that should be resolved by political means.

The question of the continental shelf involves the notion that the many islands have continental shelves of their own. Since Greek islands form an almost uninterrupted string along the Turkish Aegean Coast, this could exclude Turkish claims to a continental shelf.

The Turks contend that their coast has a continental shelf of its own and that this should be extended westward from the Greek islands for reasons of "equity."

Apart from openly endorsing the Greek position, the Soviets for the first time accused Turkey of blocking a settlement in Cyprus. The government newspaper Izvestia said the Turkish side "has not yet shown the good will" necessary to resolve the issue. Cyprus has been effectively partitioned since the 1974 Turkish invasion.

Perhaps the most significant pressure on the Turks is coming from daily press accounts of Ankara's martial-law policies. The Soviet press has reported that as many as 200,000 persons have been arrested in Turkey during the junta's "furious campaign of terror and violence."

News accounts and comments also suggest that the Soviets are attempting to organize a major international campaign on behalf of 52 Marxist trade union leaders on trial in Istanbul.

Earlier this week, the Soviet news media also endorsed the creation of a "broad democratic front" of exiled leftist parties including the Communist Party of Turkey with an attack on new U.S.-Turkish military cooperation and charges that the Turkish junta "with direct American support" is violating democratic rights in Turkey and keeping "tens of thousands of Turkish citizens" in jail for their "progressive views."

Moscow's sudden interest in internal Turkish policies also coincides with what Soviet sources say are Soviet assessments that the Turkish generals, after initially receiving nearly unanimous support for reducing political violence, are facing growing discontent over their hard-line policies.

The thrust of Soviet comments is that the United States is giving full backing to the Turkish junta and that this is a relationship aimed against Greece. In this context, according to these sources, Moscow expects Papandreou to assess Greece's future relationships with NATO and Washington.