TERRORISM TRACING THE INTERNATIONAL NETWORK

Four well-groomed men bearing sawed-off shotguns approach a car on a busy street in Milan; bullets rip through the body of the passenger, chief of one of the city's largest hospitals. The Red Brigades, the nation's most-feared terrorist group, claims responsibility. In Northern Ireland, a band of armed men uses explosives to blast its way into the castle of Sir Norman Stronge, an 86-year-old Protestant leader and longtime speaker of Northern Ireland's Parliament; the bodies of Sir Norman and his son, James, 48 years old, are found later, bullets through their heads, and guerillas of the Irish Republican Army (I.R.A.) say it was their work.

Such incidents -- these two within the last few weeks --are the stuff of everyday headlines. But last month, at his first news conference as Secretary of State, Alexander M. Haig, Jr. made them the focus of diplomatic confrontation. He warned that international terrorism had become "rampant," and he charged the Soviet Union with consciously seeking to "foster, support and expand" terrorists activities around the world. Specifically, he accused Moscow of "training, funding and equipping" those who kill for politcal profit.

The reaction to Secretary Haig's charges was in many ways predictable. The Soviet Union called such talk "a gross and malicious deception" and insisted that the "control center of international terrorism" was, in fact, the Central Intelligence Agency headquarters in Langley, Va. Journalists who interviewed Government intelligence experts -- including some C.I.A. aides -- quoted officials to the effect that there was no hard evidence to support Mr. Haig's accusations. And many Americans shook their heads despairingly at what sounded to them like nothing more than an old cold warrior's refrain, a broadside political attack against a safe and familiar target.

Until a few years ago, I might have been among those head-shakers. Generations of Americans, raised on Depression fare, find it hard to shake off a belief in the aspirations of the political left. But I have spent the last two and a half years researching leftist terrorists groups, talking to government officials and police in 10 countries from Sweden to Lebanon, examining court records and interviews in the public prints. I now know better. There is massive proof that the Soviet Union and its surrogates, over the last decade, have provided the weapons, training and sanctuary for a worldwide terror network aimed at the destabilization of Western democratic society.

The network, as described by dozens of captured terrorists and volumes of courtroom testimony, consists of a multitude of disparate terrorist groups, helping out one another and receiving indispensable aid from not altogether disinterested outsiders.

A few years ago, the C.I.A. reported that more than 140 such terrorist bands from 50-odd countries on four continents were linked in one way or another.