The Kremlin appears to be adopting new and tougher strategic plans in Northern Europe to defeat NATO in case of war. Already Moscow's plans are threatening the delicate superpower balance of forces that has kept the Baltic region virtually trouble-free since World War II.
Western diplomatic sources here draw these conclusions from their own analyses and from a study, released last week, by a Swedish commission. The study reported with remarkable frankness about Soviet submarines maneuvering in Swedish waters.
Indications are, the sources say, that Soviet plans possibly include using submarines to land mobile strike forces in Sweden to knock out warning and command centers. Sources speculate that the Soviet aim could well be to open the way for heavier Soviet forces to push westward to airfields in Norway available for NATO use.
The Soviets could also parachute strike forces in, but some Swedish experts believe they are at least experimenting with submarines as stealthy landing platforms. The Soviets would want to try to prevent NATO from flying nuclear weapons to the Norwegian airfields to block Soviet submarines and surface vessels heading westward to the North Atlantic, Western sources say. The Soviet vessels would come from the huge naval base at Murmansk, across the top of Scandinavia, and through the Baltic itself from Leningrad and perhaps Tallinn.
Western and Swedish sources stress that only circumstantial evidence supports their thesis. But they see it as a logical explanation for the increased number of Soviet submarines in Swedish waters since 1981.
The commission reported more than 40 incursions in 1982 alone, probably organized into coordinated operations including six submarines (three of them minisubs) uncomfortably close to Stockholm itself in October.
In a section of its report little noted so far in the West, the Swedish commission set up to examine the incursions specifically pointed to ''the recent phenomenon of military use of special troops for surprise operations.''
The next day commission member Carl Bildt, a conservative member of parliament and a specialist in defense, wrote a newspaper article saying the Soviet aim was not to invade Sweden but to knock out command and control centers , thereby opening the path to both Norway and Denmark.
The commission itself rejected other possible Soviet motives for sending in the submarines, such as training their crews or planning to station missile-carrying submarines in Swedish waters.
Instead it pointed to motives ''of a military operational character.'' Western sources draw the clear inference that the commission believes the Soviets are laying plans against Sweden itself.
The sources underline another commission paragraph noting ''signs indicating an increasing strategic role attached to the Baltic, mainly as part of an increasing importance of the Northern European and North Atlantic area in general. . . .'' Sweden, the commission said, was more exposed as a result, because it has the longest shoreline of any Baltic state.
Western sources also see other Soviet motives for sending submarines close inshore. These include spying electronically on recent tests of three sophisticated Swedish antisubmarine torpedoes that are about to come into operation here.
One of these new torpedoes reportedly punches a small hole in the submarine, forcing it to surface. Another homes in on the propeller and destroys the entire submarine. The third, nonexplosive, clings like a limpet to a submarine hull and emits electronic signals to the surface.
The Soviets are also thought to be eager to try to decipher new defense and commercial technologies Sweden has acquired from the United States and other Western countries.
The center-left Social Democratic government of Olof Palme is more circumspect in public, but its private concern, and the scope and bluntness of the commission report, has sent a stir of alarm throughout Scandinavia.
NATO planners are also studying the new situation intently. One result is that the Soviets have provoked an anti-Soviet backlash that has pleased the Reagan administration in Washington. Sweden, officially neutral but in fact well armed and the linchpin of Baltic defenses, is newly aroused against Moscow. Prime Minister Palme has suspended diplomatic overtures intended to warm relations. Instead he has opened the way for Sweden's Navy to shoot to sink instead of to warn if more submarines are found in inner Swedish waters.
In an interview here May 3, Mr. Palme gave every impression that he was ready to use the torpedoes against Soviet submarines if necessary. His government also intends to spend more on antisubmarine warfare.
The prime minister was late for our interview because he was receiving reports of what was thought to be another submarine sighting on Sweden's west coast, near Gothenburg. Helicopters and patrol boats were also checking a report on the east coast near Sundsvall.
When Mr. Palme arrived, he proceeded to call Soviet strategy both ''intolerably stupid'' and ''extremely unwise.''
Meanwhile, NATO members Norway and Denmark are newly vigilant for Soviet submarines. Norway fired more than a dozen torpedoes at a suspected submarine in the Hardangerfjorden on its northwest coast.
The Soviet submarines have also helped to make even more remote the lingering Swedish and Finnish hopes of banning nuclear weapons from the Nordic area, although Palme said May 3 he remained hopeful.
A closely informed Western diplomat comments: ''Palme wasn't doing at all well on foreign policy until the commission came out naming the Soviet Union and revealing the scope of Soviet activities. Now he has come down hard on the Soviets, and the Americans are watching with approval.''
Mr. Palme said that Sweden had to show a credible defense strength if it was to maintain its policy of nonalliance in peace and neutrality in war. It could not allow (1)the Soviets to gain the impression that Sweden was weak, (2)NATO to think it could use Sweden against the East, or (3)the Soviets to imagine they could use Sweden against NATO.
''That's why it's so important that we chase these submarines,'' he said.