Last week members of the worldwide peace movement temporarily had to ease up on their demonstrations against American militarism. These are turbulent and unpredictable times, and last week the world's greatest threat to peace was Sweden. To see Sweden, of all nations, lusting for violent confrontation must have been very distressing for peace activists everywhere. Remember the Stockholm Peace Congress? Remember the Swedes' exemplary neutralism over the past few decades? Yet in Sweden the pendulum has apparently swung back again.

Imaginel A small, obsolescent Soviet submarine runs aground while on a training mission in Sweden's tricky coastal currents, and the Swedish military starts rattling the saber. The Swedish politicos make political hay. Meanwhile, the lives of every youngster on that submarine are endangered, and the Soviets are depicted as warlike and devious -- the same old stereotype. Such primitive political grandstanding was never committed when Olaf Palme and his Social Democrats ruled in Stockholm. However, Palme is now in the minority, and the Swedes are engaging in the same crude anti-Sovietism as the Reagan administration. It will not be good for Europe.

Last week the Swedes followed a very reckless course. Why all the menacing oratory? Why all the fatuous legalism? Why not simply salvage the sub and send Moscow the bill? After all, the Soviets were obviously embarrassed enough. Is it really wise to intensify their deep sense of insecurity? It is prudent to humiliate them when they have so many other worries: their defensive action in Afghanistan, the bellieose Poles, another uncertain wheat crop, and all those malicious charges in the Western press claiming the Soviet Union has developed the ghastly chemical and biological weapons now being used to annihilate Southeast Asians? With the Swedes acting like cowboys, what chance will there be for a nuclear-free zone in Scandinavia?

Actually, through the whole imbroglio, the U.S.S.R. behaved very well -- a point that doubtless has not been missed by such thoughtful American observers as Anthony Lewis of The New York Times and George Kennan, the seasoned student of Kremlin affairs. In the face of every Swedish provocation, the Soviets were restrained, mature and even somewhat droll -- the sub's captain drawing his forefinger across his throat when asked the fate awaiting him back home -- haha, that is good one.

As for the captain's insistence that the sub had foundered owing to a faulty gyro and inclement weather, I find the explanation perfectly reasonable. Surely the Swedes are familiar with the technological wizardry of the Socialist Fatherland. In Russia, a lot of junk wobbles off the production line. How well I remember the adventure of that South Korean Boeing 707 that, while on a commercial flight in April 1978, wangered into Soviet airspace undetected by the Soviet air defense system. Norwegian radar had spotted the plane immediately, but it was not until the airliner lumbered over one of the comrades' heavily guarded, top-secret military installations -- a flight of at least 18 minutes -- that they caught on and scrambled to their Migs. In the ensuing hysteris, they blasted away at the plane killing two civilians and wounding 10 others. Then they lost the plane completely for an hour and a half. The thing flew all over northern Russia before landing on a frozen lake.

I have long held that it was during this chilling episode that the world experienced World War III. The Soviets are worriers. As soon as they lost sight of that damaged airliner, my guess is that they let fly against all their enemies with every missile in their arsenal. It is just that things do not work very well in Russia. We do know that a few days later President Brezhnev looked very haggard during meetings in West Germany. According to the press, he consumed a bottle and a half of vodka.

What should have been borne in mind by everyone last week is the point Kennan recently made in The New Yorker, to wit: the U.S.S.R. is essentially a defensive power. If that sub was indeed gathering intelligence information, let us recall that Russia has been invaded many times. Swedish arthies have fallen upon the Russians as recently as 193 years ago. The Russians have legitimate defense interests in the Baltic, as this frightening display of Swedish chauvinism makes clear.