WHILE RONALD REAGAN was chuckling this weekend at Rancho Cielo over his successful political maneuvers both in the Senate and on the borders of Nicaragua, there were surely some equally gleeful chuckles deep in the heart of the Evil Empire.

What do the Soviets have to chuckle about now that their jig is up in Central America and the U.S. is ready to confront ruthless communist aggression head on?

Well, the Soviets have seen this show before. And while it appears that Reagan has come out on top in the first act, the Gipper would do well to remember the words of another great coach, Dick Motta, who during the 1977 NBA Championships warned the denizens of the nation's capital that, "the opera isn't over 'til the fat lady sings."

Let's just suppose that all of the Reagan Administration's worst fears about the Soviets are true: that they are hell bent on destroying freedom and democracy wherever they can; that they are planning to take over Central America through their surrogates in Havana and Managua; and that they funnel arms and aid to every terrorist, drug trafficker and general bad guy in both hemispheres.

Let's suppose that there really is a Soviet functionary--call him Elliotski Abramski--whose job is to make sure that Central American governments put the interests of World Communism and the hegemonizing superpower ahead of their peoples' freedom and well-being.

Well, what could please Commissar Abramski more than a war in Central America? What better way to arm communists in the region, or to destabilize its fragile governments, than to create a war that is sure to destroy much industry and agriculture, to radicalize and embitter the peasantry and to make Soviet allies ever more dependent on aid and military support from Moscow?

And when your cold war rival starts the war for you and chooses to support a band of defeated and discredited ex-facists who are reknowned above all for their predeliction for killing, well, what more could you ask for?

OF COURSE, the conflict on the Nicaraguan border is hardly a conflagration. It has been more like a smouldering cigarette butt, so far. But these fires have a way of getting out of control rather quickly. Remember how low key the conflict was in Vietnam in 1964, and how quickly it overwhelmed not only that nation, but Laos and Cambodia as well.

The governments in Latin America seem to remember. Several South American nations--among them Argentina, Brazil and Columbia--have joined the Contadora group of Central American countries in publically opposing aid to the Contras and calling for the U.S. and Nicaragua to negotiate a peaceful resolution to regional tensions--something the Sandinistas have repeatedly offered to do, and the Reagan Administration has refused repeatedly.

Instead Reagan has engaged in a campaign of red-baiting abroad and at home. His penchant for intervention abroad threatens to destabilize the Middle East as well as Central America. His charges that congressmen who opposed the Administration's aid package to the Contras were either supporting communism, or being duped by those who do, echoed those of another great name caller, Senator Joe McCarthy, who campaigned against what he called "a conspiracy so immense" that it extended from Moscow to the heart of the U.S. government.

There may very well be such a conspiracy under way right now. But if the plot is to destabilize Central America and foment revolution there, then a simple analysis of U.S. policy locates the center of the cabal at 1600 Pennsylvania Avenue.