A new act in what is called here the ''submarine drama'' is alarming both Sweden and Western diplomats. Both are now searching for Soviet diplomatic as well as military objectives.
Only days after a strong Swedish protest against an estimated 40 Soviet submarine intrusions last year, two more sightings have been reported in Sweden and another in Norway.
At this writing, no submarine had surfaced, and two of the searches have been given up.
But evidence seemed stronger May 5 that a minisubmarine may have penetrated to within five miles of a small coastal city on Sweden's east coast.
All over this country of 8.5 million, with a centuries-old tradition of neutrality, people are saying: ''Enough is enough. When are the Russians going to stop this?''
Swedes take it for granted that any alien submarines come from the Soviet Union, especially now that a government commission has openly named the Soviet Union as being responsible for the intrusions.
As the Swedish Navy detonated two fixed seabed mines and dropped depth charges to try to capture the reported submarine on the east coast at Sundsvall, both Swedish and Western sources admitted to considerable concern about Soviet motives and timing.
Commented one senior diplomat: ''It's almost as if the Soviets are saying to Sweden: 'Look, you will just have to accept a certain loss of sovereignty now. We intend to keep on acting as we please, and meanwhile, you'd better keep on good terms with us.' ''
Diplomats see this attitude, if true, as a basic misreading of the Swedish character. Sweden may be neutral in a military sense, but it is firmly part of the Western world in outlook and values.
Sweden's Prime Minister Olof Palme is a Social Democrat, but he is also extremely angry at the wide scope and the effrontery of the Soviet submarine intrusions of the last two years.
When the recent commission issued its report, Mr. Palme made it clear that his government would no longer try to warn off intruding submarines, but if necessary, would shoot to sink them with new types of sophisticated torpedoes which come into service this summer.
In line with this new toughness, which is widely supported within Sweden, it detonated seabed mines off Sundsvall and dropped depth charges much sooner after the initial
sighting than in previous cases.
Each new sighting brings a wave of bold newspaper headlines, page after page of maps and comments, additional television news programs - and rising concern, particularly among older people, that the Soviets might be preparing some kind of strike against Sweden itself.
When the Navy detonated its mines off the Sundsvall coast near the island of Alno, on which many people have summer cottages, residents came into the streets in alarm and half expected to see Russians landing.
Here in Stockholm, Soviet Ambassador to Sweden Boris Pankin appeared unexpectedly at the Cabinet Office amid reports that he had been summoned to receive a new protest.
Western diplomats speculate that Soviet diplomatic objectives might include trying to ''Finlandize'' - render less independent - Swedish foreign policy. This could involve encouraging the Swedish peace movement in its opposition to positioning cruise and Pershing missiles in Western Europe.
Swedish analysts wonder whether the Soviet military might be acting on its own under a general directive from the Kremlin. Some also feel that the Soviets might be trying to strike back at the West because of President Reagan's hard-line rhetoric in recent months. Each new reported sighting makes the Swedish government more determined to spend extra funds on its antisubmarine defenses - a development quietly welcomed by the US and by NATO itself.