The president has only to send a modest detachment of U.S. Marines to Lebanon as part of a multinational peacekeeping force and senators from Kennedy to Goldwater insist they can stay there only if they are not shot at. No sooner does the Pentagon mount a mammoth military exercise in Honduras than some 50 House members fire off a letter to the chairman of the Armed Services Committee, urging that any "reprogramming" of defense funds for this purpose be denied.

Enough of these "cream-puff" congressional constraints on presidential war-making decisions, cries Rep. Don Edwards. Impeachment is the only way to stop Ronald Reagan's "illegal war" against Nicaragua.

That's what is known as the Vietnam syndrome at work. It's an identifiable political force. But it is by no means a rounded expression of the American mood and mind-set on how, where or when to employ American power around the world. There is another force at work: a positive appetite for instant display of American muscle, for showing the flag at minimal risk and low cost.

As evidence of this confounding ambivalence, I would cite the almost deafening ho-hum that greeted Ronald Reagan's commitment of U.S. armed forces and prestige to the conflict in Chad. 4 That's C-H-A-D, a desolate and destitute northern African country twice the size of Texas with less than one-third the population, no mineral treasure and no real connection with the United States. A former French colony, its security is primarily and properly the responsibility of France. But its landlocked location next to Nigeria, the Sudan and other countries of critical concern to U.S. policymakers makes it "strategic." The aggressor is Libya's rapacious Col. Muammar Qaddafi. If Chad goes, State Department authorities argue, there goes the neighborhood.

So the president, having already rushed $25 million in emergency military supplies, including anti-aircraft weapons and a half-dozen U.S. military trainers, has now deployed two AWACS reconnaissance planes, eight F15 fighters, and some 550 ground personnel to adjoining Sudan.

As required under the War Powers Act, he has formally notified Congress that the AWACS will stay there for a "limited" but undefined time to support the government of Chad "and other friendly governments assisting it." He specified that the U.S. planes "are equipped for combat."

Now, that may sound like no big deal. But if we are talking about places where U.S. forces could get caught up directly in a shooting war, Chad is no less likely a candidate than Lebanon --or Central America. When the president spoke of "other friendly governments," he had in mind that the French would provide fighter planes to counter Qaddafi's bombers and the AWACS would use their warning capability to locate the bombers and their control capability to guide the French planes to their targets.

France's cautious Socialist government has been holding back on its end of the deal. But Chad's fortunes look grim, and even their limited commitments would make it hard for either France or the United States to let Qaddafi win. So you cannot exclude that the AWACS will be called into play or assume that Qaddafi is bluffing when he says he'll try to shoot them down. Enter the American F15s. Enter the United States, not just as a remote-controller but as an active participant in Chad's war.

Yet, you have to strain to hear any alarms from the congressional watchers on the ramparts. True, it's August and Congress is dispersed in recess. Nobody can say how the confrontation in Chad will evolve or how a reassembled Congress may yet react. And, true, some part of the explanation for the early nonreaction has to do with the importance of appearances to public (and political) opinion.

A desert doesn't have the look of a quagmire. If chasing guerrillas in El Salvador evokes "Apocalypse Now," high-altitude, high-speed, high-technology warfare evokes "Star Wars." Chad evokes "Beau Geste." Though Qaddafi has all sorts of Soviet encouragement, he is not some cog in a complicated, Marxist-Leninist, global conspiracy. Qaddafi is the high-profile, homicidal weirdo that you love to hate--and beat.

Remember the unseemly hoopla--Ronald Reagan's in particular--when U.S. planes shot down two Libyan jets over the Gulf of Sidra. Even more to the point, remember the way Gerald Ford's Oval Office resembled the winning team's locker room after the bungled and costly rescue of the crew of the Mayaguez? It was America recovering its pride after its shattering Vietnam loss.

The two are of a piece. And so is the--until now --restrained public response to the particular nature of the American involvement in the war in Chad: swift, surgical and successful, presumably. It is in exactly this sense that the Chad affair helps to define what kinds of projections of American power are likely to be relatively acceptable to American public opinion, in much the way that El Salvador and Nicaragua define what kinds are not.

If there is a Vietnam syndrome working on the public psyche, there is, not far from the surface, a Mayaguez syndrome, as well.