TERRORISM INFLICTS many kinds of burden on a society. There's an illustration of truth in the melancholy circumstances under which Arrigo Levi, the editor of La Stampa of Turin, is leaving his newspaper. Italy's better papers are currently being produced under conditions that amount to siege. The gunmen of the ultra-left have made a special target of people in the news business, and it takes extraordinary courage to keep printing the kind of reporting and commentary that offends the terrorists.

For some time Mr. Levi has worn a bulletproof vest as a matter of course. He moves around his city under police guard. A year ago his deputy editor was shot dead by four young men. Turin has been a center of political violence in recent years, and perhaps La Stampa attracts more attention from the radicals than most papers because its owner is Fiat, the automobile company. The strain of living and working under those conditions wears people down. After five years of it, Mr. Levi has resigned and intends to live in London for the coming year.

The terrorists' gunplay is highly selective, and its effects are rarely visible to the eye of a casual visitor to Italy. But two people have been killed this month alone - a magistrate and an expert on medical evidence. The victims in these murders are always connected one way or another with democratic political life, or the administration of justice, or industry.

The Red Brigades tried to destroy the Italian political system last spring when they kidnapped and killed Aldo Moro. But the same government remains in power. The courts continue to try to convict terrorists. The newspapers continue to publish denunciations of them. The effects of this long series of political assassinations has been far less than you might reasonably have expected. But they have produced an atmosphere of menace in which it requires a continuous display of fortitude for people in many kinds of jobs to meet the normal responsibilities of daily life. That exertion imposes an immeasurable cost on civilized life, and one conspiciuous indication of it is the departure of Mr. Levi.