Only the people seem to know what President Reagan is up to in Central America.

According to a Gallup Poll, people who never see the cable traffic and/or attend CIA briefings said they think that the president is taking us into a war. They thought so, incidentally, even before the latest bellicose moves: the dispatch of warships to both coasts of Nicaragua; the step-up of subversion against the Sandinistas; the increase in military training personnel, weapons and economic aid and new and enlarged joint maneuvers with the Honduran army.

Seventy-one percent of those interviewed said they believe that the president is leading us into a Vietnam-style involvement in El Salvador.

And why is he doing it? Why is he driving from the front page the good news about the economic recovery? Why, as he seemingly prepares to announce his candidacy for reelection, is he burnishing his warmonger image? Why is he squandering his enormous political capital on a war that nobody, beginning with the generals, wants to fight?

Why would a "nice guy," who after ordering out the fleet uses his Saturday broadcast for an emotional appeal for a liver transplant for a dying child, set in motion events that could cause the death of thousands of people who are barely living as it is?

Two years ago, when Alexander M. Haig Jr., then secretary of state, was fulminating about a blockade against the revolutionary government of Nicaragua, the politically aware types around the president, White House chief of staff James A. Baker III and deputy chief of staff Michael K. Deaver, were winking at reporters and saying, "That's just him. We're not going to war."

Nothing has changed, except the president's approach.

"Our" side in El Salvador has continued to show its lack of will and skill to knock out the rebels.

Our "secret" war in Nicaragua only served to strengthen the Sandinista government. No more proof of massive arms shipments from Nicaragua to El Salvador, the overt reason for the intervention, was offered. And provocative presidential speeches about "fire in our front yard" did not budge the public an inch from its total aversion to the idea of another jungle war. Nothing that was said or done persuaded our Latin American neighbors. Our European allies, who also remember Vietnam, did not rally.

The Linowitz Commission said negotiations, on a grand scale, were the only way out. So did our Latin-American neighbors in the Contadora Group; they offered to mediate.

The Joint Chiefs of Staff, through retiring Gen. Edward C. Myers, conveyed its conviction that it was "not in the national interest" to send U.S. troops into El Salvador without the support of the American public.

Pentagon dissent does not stop at the top.

Sen. Gary Hart (D-Colo.) says that in his capacity as a member of the Senate Armed Services Committee he receives, from middle-level officers, warnings of more drastic schemes afoot to overthrow the Sandinistas and reassert gringo supremacy among the peasants.

But Reagan is listening to other drummers: to such fanatically anti-Soviet counselors as national security affairs adviser William P. Clark and U.N. Ambassador Jeane J. Kirkpatrick, who apparently see nothing wrong with a blockade, or anything else the administration might do, to further the doctrine of "better-dead-than-red."

As he ambles toward the brink, the president is obviously counting on Congress. Even the doves are benumbed by his boldness. They are wary about voting against the illegal war in Nicaragua.

Given a choice between being blamed for acquiescence in starting another jungle war and being blamed for "losing" El Salvador, they flop and moan and wring their hands.

They remember, as Reagan does, how harshly the public can deal with a president who, like Jimmy Carter, does not exert U.S. power. Reagan has usurped the dialogue to the point where, according to Hart, "The Democrats are nervous about voting against a secret war without putting something in its place."

Reagan does not flinch at the idea of a new Vietnam.

It would be fought by mercenaries rather than draftees, for one thing. Besides, Reagan said he thought the old one was "a noble cause."

Many Republicans would like a rematch with a small, uppity, leftist country. Rep. Dick Cheney (R-Wyo.), for instance, says that the lesson of Vietnam was that "we did not do enough."

Five hundred and twenty-five thousand troops, 57,939 deaths inscribed on the black wall of the Vietnam Memorial, more bombs than World War II, $50 billion and a decade of turmoil were enough for most Americans.

The country is saying, "There he goes again."

Washington is saying, "It might work."

If the people want to stop Reagan, they'll have to do it themselves. That's the only thing that is clear about the situation.