Speaking privately, U.S. officials deny that President Reagan is spoiling for a swipe at training camps for Salvadoran rebel hit teams in Nicaragua. You can forget the rumors that he is itching to offset the impression of weakness conveyed by failure to retaliate for the bombing of the U.S. Marine compound in Lebanon, or slaying of Americans in El Salvador last June, or the hijacking of TWA Flight 847.

Quite the contrary, we are told. The recent stiff note to the Sandinista government in Managua means simply what it says: the United States has good reason to think the Sandinistas are schooling "terrorists" for attacks on "U.S. personnel" in Honduras and that it had at least a hand in the shooting of the six Americans, including four Marines, in San Salvador. Any more of that sort of stuff will have "serious repercussions" is all the United States was saying. Deterrence, not stage-setting for a show of strength, is all the administration had in mind.

I believe it -- up to a point. That is, I believe that there is a powerful restraining force at work in the Reagan administration and that it resides in a high place. It was Ronald Reagan, by his own account, who held back after the Marine bombing. His was the loudest voice of prudence at the time of the TWA hijacking. It was his concern for "collateral" loss of innocent lives, I'm told, that weighed most heavily against a plan to strike at suspected Nicaraguan training camps right after the killings in El Salvador.

That said, the possibility that the administration will feel compelled to conduct a "surgical" U.S. air strike at Nicaraguan targets by no means diminishes. Deterrence is a dicey business. It becomes all the more chancy when you take into account the nature of the forces at work against restraint.

The Sandinistas say, in effect: Look, no hands. No matter, we say: The intelligence evidence constitutes a solid case for holding Nicaragua responsible in a general way for future hostile acts against one form or another of the American presence in Central America -- military, diplomatic, civilian. The crucial question then becomes whether the Sandinistas can be convincingly held responsible for even those anti-American terrorists acts that can be traced directly or indirectly to Nicaraguan nests for terrorist training?

Obviously, we are not talking about a court of law. But we are talking about possible acts of war and about the prospects for Nicaraguan responses and U.S. escalation, for which there could be a need at some point for a measure of American public understanding and support. The Nicaraguan provocation, then, must not only be real but as a practical matter it will have to be presentable in a way that will make it look real.

This, in turn, presupposes a level of Nicaraguan regimentation over the dirty tricks it sponsors that the U.S. government disavows for its own activities. Responding to the recent U.S. note, Nicaraguan President Daniel Ortega said: "Nicaragua has neither practiced nor supported terrorism, nor has it been involved in any terrorist act." More specifically, the Sandinista foreign ministry formally declared that, "Nicaragua rejects any suggestion at all of responsibility for what happened . . . in San Salvador or in any other similar situations that occur in that or any other country."

You don't have to believe a word of all that to hear an echo in the disclaimers of CIA Director William Casey in an interview last June with U.S. News and World Report. He was asked about any connection between his agency and a car-bombing by a Lebanese counterterrorist group last March that killed 80 people but missed its target, the leader of an extremist and violence-prone Shiite movement. "We worked to strengthen (the Lebanese government's counter- terrorist) capabilities, (to) train them, give them technical support. But they do any operations themselves. We were not involved, and no one we had trained was involved in the Lebanese car-bombing operation."

Careful words -- careful enough not to rule out what is thought to have happened: the U.S.-trained Lebanese counterterrorist forces subcontracted, so to say, the car-bombing to free- lance terrorists, who did the job. The point is simply that if U.S.-backed Lebanese counterterrorism can get out of U.S. control, it is not too outlandish to believe that, given the nature of terrorism and those who practice it, the same could happen in the case of terrorism, Nicaraguan-style.

It is this possibility -- that the Sandinistas are no more capable of controlling events they set in train than Bill Casey claims to be -- that makes an already precarious game of chicken even more precarious. Going public with previous private warnings to Managua plays into the hands of the hard-liners in the president's midst, the more so since previous threats of retaliation have gone unfulfilled.

The result is that almost any new anti-American terrorist incident in the neighborhood, however remote its connection to Nicaragua, could put Ronald Reagan's prudence-in-practice to its heaviest test.