COURAGE AND STAMINA are qualities that can win great rewards in government. For Italy's government, they have won a historic triumph over the Mafia. The trial in Palermo of 452 defendants, begun 22 months ago, has now ended with the conviction of three-fourths of them and verdicts that include, for 19, life sentences. It would be naive to say that the Mafia has been permanently crippled. But much of its leadership is apparently among those convicted.

All of the judges, prosecutors, jurors and police who took part in this enormously complex proceeding did so at great personal risk. By the late 1970s, Mafia murders were in the range of 500 a year, and political rank was no protection. In 1980 the president of the Sicilian regional government was assassinated for having attempted to interfere with construction racketeering. Two years later the head of the Sicilian Communist Party was similarly shot down. The government then sent to Sicily the Carabinieri general who had run the successful battle against the terrorist Red Brigades, and four months after his arrival, while driving through the center of Palermo, he and his wife were shot dead.

Until then, the Italian government had never taken any very forceful action against the Mafia. Ever since the Fascist experience, Italians have preferred to keep their police organizations weak. Cynics also observed that the Mafia controlled many votes as well as much money. But the murder of the general finally brought a reaction. The government gave the police wider investigative powers, and prosecutors began to move as they had never done before. Three years ago, for the first time, a Mafia chieftain under arrest turned state's evidence. Last week's verdicts were the result.

Italy's struggles with political terrorism in the 1970s attracted enormous attention, and deservedly. But the Red Brigades at their height were never the threat to the integrity of the Italian government, and to the basic decencies of Italian life, that the Mafia had become. These verdicts are an important blow against the worldwide traffic in drugs and will have direct benefits to the United States. More important, Italy has begun to bring to justice a criminal conspiracy swollen to a degree of wealth and arrogance that seemed for a time to challenge the state itself for control of parts of the country.