IT IS IMPORTANT to be clear about the report in this newspaper that a counterterror program set up by the United States in Lebanon got out of hand and spawned an unauthorized car-bomb mission in Beirut in which more than 80 persons were killed, many of them innocents; the ostensible target, meanwhile, was spared. This event was an act of terrorism no less horrendous and reprehensible than any the United States intended to counter.

Fixed from the start on the perils of terrorism, the Reagan administration found its darkest fears confirmed by attacks on Americans in Beirut. It responded -- in the doctrine that finally prevailed after a strenuous internal argument -- with repeated public warnings of its intent to preempt and punish the attackers, even if the evidence was not of courtroom quality and even if innocents were endangered.

The administration also responded, it now turns out, with a CIA program to set up several foreign- manned counterterror teams in Lebanon. The members of one blew up a car bomb March 8 outside the Beirut house of Mohammed Hussein Fadlallah, leader of a fundamentalist Shiite group called Hezballah. It was reportedly an unauthorized mission. But one wonders whether the killers felt they were unauthorized. The hit squads were then reportedly disbanded.

What remains so distressing is the utter predictability of the whole sequence. It took no crystal ball to imagine that the operation made the United States hostage to people with their own ways and priorities. Nor is it a surprise that word of a calamity of these dimensions eventually leaked.

The United States has lost a major part of the moral advantage it claimed as a victim and enemy of terrorism. It is exposed now to the consequences of being seen to have had some of its chosen associates attempt an assassination and kill many people. American officials link the intended victim, with a good deal less than courtroom evidence, to a series of terrible attacks. But he is known to many Lebanese as their spiritual leader. And his help has been sought to trace Americans kidnapped in Lebanon.

Disclosure of the Beirut bombing finds the CIA's congressional overseers caught -- not for the first time -- between sharing responsibility for a fiasco and acknowledging that their oversight was casual. They should have known better. The principal responsibility, nonetheless, falls on a president captivated by thoughts of fighting fire with fire. Terrorism is a menace, but, even in its extreme Lebanese form, it is not the ultimate menace, and a democracy must be prepared to accept restraints on its fight against it. To think that the United States carelessly contributed to the general slaughter is a source of shame.