President Tito's successors are moving cautiously to improve Yugoslavia's strained relations with the Soviet Union. At the same time, they are attempting to foil what they regard as a Soviet-masterminded propaganada campaign designed to justify possible future Kremlin interference here.

Both strands of Yugoslav policy toward Moscow have been evident during the visit here this week of a Soviet parliamentary delegation headed by First Vice President Vasiliy Kuznetsov. While welcoming Kuznetsov's presence as a first step toward putting Soviet-Yugoslav relations on a stable basis for the post-Tito era, Yugoslav officials made it clear that serious disagreements remain, particularly over Afghanistan.

Symbolically, Kuznetsov's arrival in Belgrade coincided with the lastest round of a continuing skirmish between the Yugoslav and Soviet Bloc news media. The latest broadside was fired by the Yugoslav side in the person of Milika Sundic, Radio Zagreb's top foreign policy commentator and an expert on Soviet propaganda techniques.

In a commentary that was also carried by the official Yugoslav news agency Tanug, Sundic replied for the first time to Soviet press attacks on President Carter's visit here last month. The Soviet media objected to Carter's repeated statements of support for Yugoslav independence on the ground that Yugoslavia was not being threatened by anyone and that the United States was trying to foist its protection on a reluctant country.

Yugoslav officials interpreted the Soviet criticism of Carter as an indirect warning to them not to become too close to the West. Sundic, in turn, accused Moscow in a sharply worded commentary of attempting to play the role of Yugoslavia's defender. He added that Yugoslavia was fully capable of looking after itself.

Since president Tito's death two months ago, Yugoslav leaders have pledged to continue his policies of strict nonalignment in world affairs. The Yugoslavs want to be free to determine the nature of their nonalignment for themselves, rather than having it defined for them by Moscow.

To outsiders, it might seem that the Yugoslavs are over-sensitive to every nuance in the Soviet press. Their reply is that it is only through a well-developed sense of paranoia that they have managed to safeguard their independence since becoming the first communist country to break away from the Soviet Bloc in 1948.

As a former senior Yugoslav Foreign Ministry official put it recently in a private conversation, "Taken individually, critical comments in East European news media might seem to you unimportant and best ignored. But we constantly ask ourselves what lies behind them and what is the aim of the people who are writing them."

Yugoslav foreign policy experts believe there is a propaganda until in the Kremlin intelligence apparatus whose role is to coordinate East European press attacks on Yugoslavia. In the Yugoslav view, different roles are assigned to the news media of diffferent Soviet Bloc countries but the ultimate aim is to lay the propaganda groundwork should the Soviet Union decide to move against Yugoslavia in the future.

Beginning with Tito's lengthy illness, which resulted in his death on May 4, Yugoslav experts have detected two complementary threads to Soviet-inspired comment about their country. The first is to bestow lavish praise on Tito himself, sescribing him as a lifelong friend of the Soviet Union and glossing over his acts of defiance to Moscow. This puts the Kremlin in a position later to accuse Tito's successors of departing from his heritage.

The second strand of Soviet stragegy has been to accuse the West, and particularly the United States, of planning to interfere in internal Yugoslav affairs. The implication is that Yugoslav's "socialist friends" reserve the right to come to the country's defense should "Western pressure" become to great.

Arguments about Soviet intentions toward Yugoslavia on the basis of press coment tend to start going in circles quickly. Soviet Block commentators could claim that all they are trying to do is reject unfounded Western allegations of hostile intent toward a nonaligned country. The Yugoslavs, however, are still deeply suspicious of the Kremlin's long-term strategy in the Balkans.

The dilemma facing Yugoslav leaders is that, while remaining on their guard, they also need good relations with Moscow for both economic and political reasons. Apart from anything else, the Soviet Union is Yugoslavia's largest trading partner and an important supplier of oil.

Relations reached a low point at the beginning of this year when Yugoslavia came out strongly against the Soviet invasion of Afghanistan, having already opposed the Vietnamese move into Cambodia and Cuban attempts to tilt the nonaligned movement in Moscow's direction. Since Tito's death, contacts between Belgrade and Moscow again are being stepped up gradually -- but there is little chance of any major rapprochement in the near future.

The Yugoslav tactic is to keep talking, but to reply sharply to any hint of Soviet bullying. This explains the double-edged welcome Kuznetsov received in Belgrade this week.