The whole scenario sounds like a grade B movie from the 1950s, but that, alas, does not mean it is not true. It's almost unbearably unfashionable to say so, but there is a plan to create a communist Central America which, if successful, will have momentous consequences for our security and that of our European allies, for Israel's international position, and for the unfortunate people of Central America. So far, Congress seems unwilling to make a serious effort to prevent--by means short of war--these human and strategic catastrophes.

Even though a very well organized lobby works indefatigably to confuse the moral, political and intellectual questions involved in U.S. policy toward Central America, there is growing clarity about the issues and the stakes. Indeed, what distinguishes the current debate about military and economic aid for Central America from similar disputes about China, Cuba, Vietnam and Nicaragua is that we have fewer illusions and more information.

We know by now what the government of Nicaragua is and what it intends--in El Salvador, Honduras, Costa Rica, New York, Jerusalem. We know who the guerrillas in El Salvador are, where and how they get their arms, what their plans are, who their friends are.

As recently as July 1979 it was possible for American policymakers of optimistic disposition to suppose that, if they acted wisely and generously, Nicaragua would emerge from its bloody civil war with an independent, pluralist, socialist, neutralist government. To this end, the United States rushed some $24.6 million in emergency food, medical and reconstruction assistance to the FSLN on their triumph, provided $118 million direct economic assistance in the subsequent 18 months, and assisted the new government in securing, in addition, some $262 million from multilateral lending institutions (an amount almost double the amount the Somoza government had received in the preceding 20 years). But before the Carter administration left office in January 1981, the decision was made that Nicaragua no longer met U.S. requirements for assistance, its pattern of internal repression and external aggression being already clear. And during the subsequent two years, Nicaragua's facade of democratic intentions and national independence have been not ripped off, but cast aside.

Everyone who cares to know now understands that the government of Nicaragua has imposed a new dictatorship; that it has refused to hold the elections it promised; that it has seized control of all media except a lone newspaper that it subjects to heavy prior censorship; that it denied the bishops and priests of the Roman Catholic Church the right to say Mass on television during Holy Week; that it insulted the pope; that it has stifled the private sector and independent trade unions; attacked the opposition; driven the Miskito Indians out of their homelands--burning their villages, destroying their crops, forcing them into exile or into involuntary internment in camps far from home.

Persons interested in such questions understand, too, that Nicaragua's rulers have introduced into the country many thousands of Cuban teachers, trainers and supervisors, including at least 2,000 military advisers. The Sandinista rulers have denied their international supporters the comforts of ambiguity. They have explained who their friends are and what convictions guide them.

From Moscow and Managua they have announced their principles: "We guide ourselves by the scientific doctrines of the Revolution, by Marxism-Leninism," Minister of Defense Humberto Ortega explained to his army; ". . . our political force is Sandinismo and our doctrine is Marxist-Leninism." "Marxism-Leninism is a fundamental part of the Sandinista ideology," said another member of the junta, Victor Tirado Lopez. They have issued a new stamp with a picture of Karl Marx and excerpts from the Communist Manifesto.

Nicaragua's leaders are done with dissembling. They are proud of their ideology, proud of their monopoly of power, proud of their huge new military force (which has no peer in the region), proud of their role in Central America's guerrilla war, proud of their string of successes in international diplomacy. Those successes are impressive: a seat on the U.N. Security Council, a stymied regional diplomatic initiative, continued support from the Socialist International and a resounding victory at the Delhi Summit of the Non-Aligned Movement. Proud too of their friends, including: Libya, the PLO and, of course, Cuba, their constant companions. The PLO connection, acclaimed by Yasser Arafat at the revolution's first anniversary (". . . the Nicaraguan people's victory is the victory of the Palestinians. Anyone who threatens Nicaragua will have to face Palestinian combatants."), has spawned international progeny. This past week a Latin American preparatory meeting on Palestine has been held in Managua for the purpose of "obtaining governmental and nongovernmental support for the Palestinian cause" and "opposing" Israel's aggressive policy. According to Radio Sandino, delegates from some 20 nations and 10 U.N. organizations were expected.

Such conferences are but one manifestation of the junta's vocation for public diplomacy. Other examples may be observed on U.S. television and, especially, at the United Nations where, with dazzling chutzpah, Nicaragua's leaders last week pressed their demand for immunity from attack by anti-Sandinista Nicaraguans, at the same time they stepped up support for Salvador's guerrillas.

The character of El Salvador's guerrilla struggle is no more ambiguous than that of Nicaragua's government. Since the elections of March 1982, nobody even pretends that the FMLNNenjoys popular support, is "really" a bunch of agrarian reformers, or a coalition that would, if victorious, usher in a more perfect democracy.

The fictions with which communist insurgents have conventionally clothed their conquest of power are not available to the partisans of the FMLN. The pretense that the FMLN is an indigenous guerrilla movement without significant foreign support has also been largely abandoned. Too many truckloads, planeloads, boatloads of arms from Cuba, Nicaragua and the Eastern bloc have been found; too many documents have been captured, too many pictures taken, too many bold announcements made from Managua. The facts about the FMLN are understood by people interested in these questions. It is a professional guerrilla operation directed from command and control centers in Nicaragua, armed with Soviet bloc arms delivered through Cuba and Nicaragua, bent on establishing in El Salvador the kind of one-party dictatorship linked to the Soviet Union that already exists in Nicaragua.

There has, moreover, been so much discussion among them of "revolution without frontiers," of "liberating" and "unifying" Central America, so many threats to Honduras, so much bullying of Costa Rica and guerrilla activity in Guatemala, that it is hardly possible seriously to doubt the regional character of Soviet/Cuban/Nicaraguan goals.

Yet to be fully faced is the relevance of these small, poor nations of the Central American isthmus to the United States, or the importance of Caribbean sea lanes to the Western Alliance. Neither is the extent of the Soviet investment --military, economic, cultural--in this hemisphere yet fully appreciated. But very reluctantly, most serious observers have come to acknowledge that, yes, the area's location gives it a certain irreducible relevance to our national interest. These serious observers grouse about the way the Reagan administration talks about the issues; they grouse about the government of El Salvador; but they understand.

The Economist noted last week that "The 'loss' of El Salvador could be a lethal foreign policy blow for America. . . ." and The New Republic made a similar observation.

There is also a growing, if grudging, acknowledgment that money--in the form of economic and military assistance--is quite probably the key to the viability of the region's non-communist governments. And two top aides of previous Democratic administrations, one a former assistant secretary of state, wrote in last week's New York Times Magazine that, "The area is of clear strategic and political importance to the United States . . ." so that "to stop American aid would be to deliver--yes, deliver--El Salvador into the hands of a guerrilla movement that is . . . allied externally with America's adversaries, and capable itself of the greatest brutality," and advised that ". . . abandonment is an option Democrats should reject."

Yet if few in or out of Congress advocated outright abandonment, a good many argued for such little assistance on such niggardly terms that the effect is almost sure to be the same.

From the perspective of hemispheric policy, it was an extraordinary week.

An official of the Soviet foreign office, Vadim Zagladin, reiterated Brezhnev's threat to install nuclear missiles in the Western Hemisphere five minutes from the United States. And a member of the Nicaraguan junta announced that, if asked, his government would consider installing Soviet nuclear missiles in Nicaragua.

In Managua, Nicaraguan officials made clear their determination to continue support for revolution in Central America while, at exactly the same time, their representatives at the United Nations demanded protection from an internal insurgency.

Meanwhile, the Democratic majority on the Latin American subcommittee of the House Committee on Foreign Affairs acted to deny the democratically elected government of El Salvador the military assistance it needs to stave off a very well armed and advised Marxist insurgency and, simultaneously, to deny a democratic Nicaraguan insurgency any support against a repressive, aggressive Marxist government--though the clear effect of such a policy would be to make the United States the enforcer of Brezhnev's doctrine of irreversible communist revolution.

If, as often suggested, the "Vietnam Syndrome" explains the extraordinary reluctance of America's political class to provide urgently needed assistance to endangered friendly governments in an area of clear national interest, in what does that syndrome consist? Obviously, the Vietnam experience did not make us isolationist. The U.S. government pursues, with the full consent of Congress, a foreign policy that involves us in the affairs of four continents. We support a large standing army and a huge defense establishment. We station troops in remote places, provide billions of dollars in economic and military assistance to governments of all sorts in Asia, Africa and the Middle East. Neither the moral nor military misgivings expressed with regard to Central America are evident with regard to these other regions.

Nobody talks about slippery slopes when we rush weapons to Thailand, trainers to Lebanon or economic aid to Africa or Asia. Nobody talks about human rights when there is murder and mayhem in Zimbabwe, though one can readily imagine the outcry if the bishops of El Salvador had issued a statement resembling that of the bishops of Zimbabwe.

Why?

Why is Congress so much more reluctant to assist an imperfect democratic government clearly important to our national interest than much less perfect governments in more remote regions?

What is it that Central America has in common with Vietnam that so repels liberals? Is it just the nature of the contest--the fact that, in both, well-financed communist guerrilla movements have simultaneously targeted the existing government and what is generally called "world public opinion"?

Is it because lobbies of the left have managed, in both cases, to make the anti-communist side seem unbearably unfashionable?

God knows there are parallels enough in the public discussion of Vietnam and Central America. In both cases, well-orchestrated international campaigns have focused mercilessly on the political and moral failings of the government. And in El Salvador, as in Vietnam, the introduction of elections and reforms, the reduction of human rights abuses and corruption have proved not to have much effect on the drumbeat of criticism. In El Salvador, as in Vietnam, Congress calls the U.S. commitment into doubt from quarter to quarter, "certification" to "certification," undermining the confidence of vulnerable allies in our reliability and their viability.

As with Vietnam, doubt is continuously voiced about whether the government of El Salvador, which struggles mightily to satisfy American demands, is morally worthy of American approval or even of survival.

But there are a few crucial differences too, and those differences involve what we know and when we know it. Not only do we know who Salvador's FMLN is, when we didn't know who the Vietcong were, we know now who the Vietcong were, how they came down from the North (20,000 in the early years alone), how they were supplied, how Western public opinion was manipulated into believing that the National Liberation Front, created by decision of the North Vietnamese Communist Party, was a spontaneous product of "deeper" social causes. We know all these things now because Gen. Vo Nguyen Giap and his colleague, Gen. Vo Bam, have told us about them.

We know too about human rights under those two Vietnamese regimes, about the labor camps and mass deportations. We know this at least in part because Stephen J. Morris' careful study has documented with endless, painful details that "The violation of human rights by the Communist Party of Vietnam, in both the North and the South, was incomparably worse than the violation of human rights by the former Thieu government in South Vietnam. The difference was not one of degree but one of quality."

We know the Vietcong did not establish a broad-based government or a socialist democracy. We know what happened--and is still happening --in Cambodia. We do not enjoy thinking much about these matters, but we know about them, just as surely as we know the character and the stakes of the contest in Central America.

The crucial difference between Vietnam and Central America is not the Pacific Ocean, though that is important. The crucial difference is that the Congress that cut off aid to Vietnam could say it did not guess what would follow.