A FAMILIAR THREAD of genuine craziness runs through the recent outbreak of terrorist bombings and assassinations in Western Europe. The targets have been NATO installations and people who make or sell arms -- within the past week, an official of the French Ministry of Defense and a German industrialist. It is pacifist terrorism at work again -- violence by people who kill to protest weapons.

It's wiser not to try to read a great deal of significance into any movement that has as few supporters as this one. But it most frequently turns up in Western Europe when strong governments are in power. The most spectacular case in the postwar years was the Baader-Meinhof group, whose shootings and robberies began at the time when West Germany under Willy Brandt was successfully reestablishing its relations with the communist countries to its east. The next eruption was a series of assassinations in 1977, during Helmut Schmidt's highly competent administration. It's not the politics of confusion or uncertainty that seems to evoke these episodes, but rather the display of assurance.

Perhaps this series of outbursts simultaneously in several countries is an occasion to note the extraordinary stability of European politics currently. Germany and Britain have installed NATO's Pershing missiles without a crisis or anything approaching it. That failure of a legitimate and rational peace movement may well have been the trigger for this very different kind of attack. In France, while President Francois Mitterrand has fallen low in the popularity polls, he is in fact leading his country skillfully through a harsh and difficult period of economic adjustment. West Germany, under the stolid and undramatic leadership of Chancellor Helmut Kohl, worries a lot about a succession of scandals, and worries a lot more about high unemployment. But business is beginning to pick up again, and, as in France, the alternatives to the present policies are neither clear nor terribly inviting. All three of these countries' governments -- the German, the French and the British -- enjoy at the moment the enormous advantage of a badly divided opposition.

It's that atmosphere of settled and rather sedate assurance that the gunmen are trying somehow to overturn. In another time, these people might have been enthusiastic infantrymen in somebody's invading army. But they were born into quiet times, and so they bomb NATO oil lines in Belgium and German servicemen's cars in Portugal. They shoot an unarmed German engineer in his home, in front of his wife, on grounds that his company makes engines for tanks and planes. The gunmen's idea is to generate a panicky sense that the very structure of society is threatened, and its foundations are trembling. But in Europe today, it's just the opposite.