THINGS ARE getting out of hand in respect to Nicaragua. The tone and, according to the latest news reports, the content of President Reagan's approach are getting progressively more threatening. Whether the Nicaraguans are intimidated is not clear. It is evident, however, that Mr. Reagan is moving rapidly toward the outer limit of the support he can reasonably expect from the American people and from this country's friends in the hemisphere. He badly needs to slow down, collect his thoughts and put them out in public view.

There is, we believe, a central ambiguity to the line the administration seems to be taking now, an ambiguity fed partly by design and partly by indecision and careless thinking. Is the American purpose merely to prevent the Sandinista rulers of Nicaragua from imposing on and disrupting the lives of their neighbors? Or is it to put an end altogether to Sandinista rule? The administration has not openly professed that more ambitious second goal, but some of its private words, deeds and plans suggest it wishes to proceed toward it, or to get the Sandinistas to believe it will. In that latter purpose, by the way, it has succeeded. The Sandinistas do believe Mr. Reagan intends to try to do them in, and they are mobilizing their considerable diplomatic and propaganda resources to block him.

Should this country try to destroy the Sandinista revolution? The reasons to say yes may be seductive. The Sandinistas are lending themselves to the purposes of foreign countries hostile to the United States. They are double-crossing the many Nicaraguans who accepted their lead in the anti-Somoza struggle. And the more the regime reveals these tendencies, the stronger the temptation in the United States to move, in one way or another, against it.

It would, however, be dangerous and wrongheaded to do so. Such an act would cut across the one principle that offers a basis on which the United States has a chance to avert far greater trouble than it has gotten into or even imagined so far. The principle is that of nonintervention.

It can never be forgotten that in Latin America, and especially in Nicaragua, the United States is viewed as the Great Intervenor. The right-wing police regimes of the hemisphere may join Washington in an effort, by open or covert means, to change the regime in Managua--but no other Latin government or element will. The substantial support the United States has received for its effort to build reform in El Salvador will inevitably fade away as Washington is seen to be returning to the role of intervenor in Nicaragua. The American public, plenty leery already, would not put up with such intervention; nor should it. The ground on which the United States stands as it asks others to oppose Nicaraguan intervention in El Salvador crumbles as the United States sponsors intervention in Nicaragua.

It can be argued that the purpose of the CIA's anti- Nicaragua operations is merely to give the Sandinistas second thoughts about their help in Salvador, not to overthrow the regime. But you have to be pretty forgetful, or pretty dumb, to buy that argument. Anyway, if there is one thing that the United States has proved itself to be bad at in recent years, it is subverting Latin regimes. There has been no "success" in this department since Guatemala in 1954, and the results there are no advertisement for more of the same.

It follows that before President Reagan goes any further he should clarify the thrust of his policy. He could state that he regards the Sandinistas as bad news, for their international connections and revolutionary ambitions as well as for their represssive domestic proclivities, but that he has decided that in order best to influence them he will forswear an intent to unseat them. Instead, he will honor the traditional hemispheric ideal of nonintervention and call upon others to join him to ensure that the Sandinista government respects that ideal in its practical affairs. The means will be hardheaded, legitimate and generally acceptable and will blunt the crippling allegation that he seeks to "intervene."

This will not tie up every loose end of American policy toward Nicaragua. But it will help remedy its central flaw. From the fundamental decision to abandon interventionism, everything else follows.