THERE IS REASON to believe that the alarm

being raised about a Libyan assassination plot resulted in the first instance from an unauthorized leak, not an authorized one. As seasoned Washington hands would know, any leak would be sure to set off a journalistic scramble to put more information on the public record. Still, the distinction is not trivial. An authorized leak of this kind suggests a casualness toward intelligence sources and a disconcerting readiness to raise public expectations of an official reprisal. By contrast, an unauthorized leak suggests "merely" that the administration inadvertently has lost control of the public play.

The discussion of the authenticity of the alarm should not be allowed to distract attention from the heart of the matter, which is the report of the plot. No one familiar with Col. Muammar Qaddafi's record of murder, subversion and aggression can doubt that it was only prudent for American officials to take seriously whatever they may have learned about his plans. A great power invites a certain mocking when it appears so concerned about a small country's supposed depredations: Col. Qaddafi could be seen on television last Sunday playing a delighted David to the American Goliath. There is all too much evidence of the capacities of dedicated gunmen, however, to indulge complacency and a misplaced pride.

Speculation has been rife that the administration might be contemplating military action--action going beyond the downing of the Libyan airplanes in international airspace last August. But the measured pace at which the administration has chosen to conduct its review of policy toward Libya-- months have gone by--indicates that any such decision is still some time off. At this point, it would be a foolish decision, we think, though some of the administration's political people may still need a little convincing on the point.

The immediate answer to a physical threat against Americans is to protect them. Otherwise, other steps are available, and necessary, to deal with the overall Qaddafi menace: order home the 1,500 American oil people in Libya, stop buying Libyan oil and try to persuade other nations to cut their links with Tripoli. Steps like these won't of themselves bring Col. Qaddafi down. He may even make a certain amount of hay out of them. But they will announce to the world that the United States does not do business as usual with a killer. That's worth a good deal.