MUAMMAR QADDAFI of Libya is back in the news, threatening to take war to the streets of America, among other venues, if the United States retaliates for the carnage in Vienna and Rome. It was a typical statement by someone who cannot really claim to be aggrieved, but stands absolutely outside the law. (One of his "diplomats," firing from inside the Libyan embassy in London, killed a British policeman outside.) Col. Qaddafi has tapped a deep vein of anti-Western and anti-Jewish feeling in his part of the world, and seems rarely to be short of killers. There are, he boasts, "millions of Abu Nidals."

But all that is not why Col. Qaddafi, who has been strewing terror since he took power in 1969, is a successful murderer. Set aside the usefulness of his Soviet and other partners hostile to the West. He could not conceivably have had a broad and continuing impact if Western individuals, companies and governments had not been ready to coddle him over the years. These range from the intellectuals who invite "understanding" for him, through the companies that provide his links to foreign services and markets, to the governments that conduct or condone dealings with him. How odd it is to talk of military operations against Libya, Israeli Prime Minister Shimon Peres notes, before political and economic sanctions had been applied.

Smart people chided President Reagan, early on, for denouncing Col. Qaddafi and trying to contain and isolate him. Their theory was that he was unwisely building up the Libyan's ego and image and advertising the inability of a democracy to cope with a criminal state. To judge by Libya's continuing defiance, American policy has failed. Yet Mr. Reagan was entirely right in identifying the Libyan as a scourge. His administration, which has taken steps to diminish American ties with Libya, and the Israelis, who are at war, are entitled to feel that others in the West have comforted a foe.

Will the Rome and Vienna attacks, whose victims were not limited to Americans and Israelis, finally stiffen some of the Europeans and the wayward corporations and make them readier to impose a freeze on the Libyan regime? There is no excuse for doing less.