Two European governments are pursuing investigations suggesting that Syria used its diplomatic privilege to plot terrorist acts on their soil. German police suspect Syrian complicity in the bomb that exploded at an Arab-German friendship society in West Berlin on March 29, while British police think Syria tried to plant a bomb on an El Al jet departing London on April 17. Britain expelled three Syrian diplomats over the weekend when they refused to waive diplomatic immunity for questioning.

What is going on? President Hafez Assad's bloody-mindedness is established -- by his slaughter of thousands of Syrians, by his use of terrorism against putative friends as well as declared foes in Lebanon, the West Bank and other Arab places, and by his continuing public defense of terrorism in the name of ''resistance'' against Israel. Still, Hafez Assad has earned a second reputation as someone who does not take foolish risks and who tailors means to long-term policy ends. Why would he expose himself to criticism and worse at a moment when he would have only Libya's company among the Arabs if Israel chose to retaliate against him, when President Reagan has just warned that he, too, would retaliate in certain circumstances, and when the abysmal performance of Libya's anti-aircraft missiles indicates that Syria's own defense may be a sieve?

There is reason to suspect that Damascus sponsored some of the terrorist acts generally attributed to Libya. There is also reason to believe that President Assad is consumed by the notion of striking at his various foes. Could considerations such as these have led him to think he could conduct a deadly policy in Europe -- at least against non-Europeans (Arabs in Germany, Israelis and Israel-bound foreigners on the El Al plane) -- even while he was assuring Europeans that Europe is off limits to terrorism? President Assad lives in a world of violence. He practices it, and his own government has recently been the target of it -- bombs went off in five Syrian cities last month, causing hundreds of casualties. There may be very few moments when defense and revenge are far from his thoughts. But he is a subtle operator, cruel to those who cross him but able to show a kindly face, as with Lt. Robert Goodman, when it is to his tactical advantage.

The Western governments do not go around looking for trouble in the Arab world. Embattled to various degrees already with Libya, they are not eager to join a second confrontation with Syria, which is not the relatively isolated, defenseless and dismissible pariah that Libya is. A self-respecting government, however, cannot avert its gaze from evident acts of terrorism in violation of its laws. The British and Germans, in investigating crimes and acting on their findings, have done the least of what they had to do.