AT EACH incident of terrorism, as now with the massacres at Israel's airline facilities in Rome and Vienna, civilized people recoil from the spectacle of savagery. The killers are, as the United States said, beyond the pale. Yet the difficulties of combating terrorism and, especially in the Middle East, of combining that task with a pursuit of peace remain formidably high.

In Rome and Vienna, local and Israeli security officers responded bravely once the bombing and shooting began. But the attackers had the advantages of initiative and surprise, and they also had safe places in which to prepare their assaults. These places apparently included Libya, Iran, Syria and Lebanon, each with its own complicity.

There is a certain consensus that a Palestinian group led by Abu Nidal, supportprimarily by Libya, made the two attacks. It is not so clear whether Abu Nidal is, as widely portrayed, a "renegade" opposed to the supposedly more moderate Yasser Arafat, or whether he is a front for the PLO chairman, as Achille Lauro mastermind Mohammed Abbas turned out to be.

What to do? The Israelis seem to be weighing going after this notorious figure if they can hunt him down, and taking another general swipe at the PLO if they cannot. On its part, the United States is caught between maintaining the principle of no free rides for terrorists and heading off an Israeli retaliatory blow so severe and indiscriminate as to collapse its shaky "peace process."

A special tension -- a double calculus of uncertainty -- is at work. First there is the possibility that Israel or the United States may use this particular provocation to hit Libya's Muammar Qaddafi, who has richly earned it for his years of terrorism and subversion directed against American, Israeli and other countries' interests. There is the lesser possibility of Israeli retaliation against targets protected by Syria's newly deployed antiaircraft missiles. Damascus made these deployments after Israel, foolishly breaking the established rules of the road, invaded Syrian airspace and shot down two Syrian planes on Nov. 19.

The United States, in one of its voices, is saying to Israel that the "peace process" will be damaged, perhaps fatally, if it strikes back too hard. Actually and unfortunately, the American initiative was foundering before the terrorists opened fire in Rome and Vienna. The mark of the foundering is King Hussein's turn from his earlier tentative cooperation with American diplomacy to his new cultivation of Syrian President Hafez Assad, who has his own ideas. To overcome his familiar and maddening hesitations and give the American initiative a chance, King Hussein needed extra political help from the United States, Israel and the PLO. He is yet to get it. The New Year, in the Middle East, looks dismal.