Two key questions have emerged in the congressional debate on the reported covert action the United States is conducting in Nicaragua: Is such a covert action legal? Is it good policy? While the arguments on the first of these questions are inconclusive, the second question can be answered definitely. Covert action in Nicaragua, at least for the purpose of destabilizing or overthrowing the Sandinista regime, is not in the national interest of the United States.

There are really two legal arguments.

The first arises from the Boland Amendment, passed last year, which states that no funds "may be used by the Central Intelligence Agency or the Department of Defense to furnish military equipment, military training or advice or other support for military activities, to any group or individual not part of the country's armed forces, for the purpose of overthrowing the government of Nicaragua or provoking a military exchange between Nicaragua and Honduras." The Reagan administration argues that is is not breaking this law because it is not its aim to overthrow the Nicaraguan government, even though this may be the purpose of the groups to whom assistance reportedly is being provided. But it is a fine point whether such an argument can be sustained when everyone knows what these groups have in mind. Until the last few days, their military leaders have been quite open about their intention to "liberate Nicaragua."

The second legal argument is derived from Article 18 of the charter of the Organization of American States, of which the United States is a signatory. The article says that "no State or group of States has the right to intervene directly or indirectly for any reason whatever in the internal or external affairs of any other State. The forgoing principle prohibits not only armed force but also any other form of interference or attempted threat against the personality of the State or against its political, economic and cultural elements." The Reagan administration argues that it is not violating this treaty provision because it is acting in self-defense. If it means the defense of the United States, the argument makes little sense. If it means the defense of El Salvador, no argument at all is presented.

The Reagan administration also contends that the treaty provision is vague and therefore must be understood in the context of all other international obligations of the United States, some of which may conflict with it. Missing from this contention is a convincing presentation of the conflicting legal requirements.

Whether a covert action is good policy is the more important question.

The interdiction of arms bound for El Salvador is the only explicit justification the Reagan administration has offered for a covert action. There is no doubt that arms are going to the Salvadoran guerrillas through Nicaragua, though there is disagreement about the volume of the flow. It is quite appropriate to attempt overt interdiction of these arms within El Salvador itself or within Honduras, provided that the respective governments give their permission. At present, however, it is undesirable to attempt covert interdiction within Nicaragua simply because the disadvantages of such an operation outweigh the advantages. There is little reason to suppose that our assistance could be limited to this purpose in the present circumstances. Moreover, a covert action is certainly not perceived in the region as an effort to block a flow of arms. Given this perception, the fact that our reported assistance may be limited to interdiction becomes less significant.

Several points can be made against a covert action whose perceived goal is the destabilization or overthrow of the Sandinista regime.

1. A covert attempt to oust the Nicaraguan government will not succeed.

One lesson of the Bay of Pigs fiasco is that even if there is domestic opposition to a revolutionary regime, as there was to Fidel Castro's, small-scale American intervention will be of no avail if it is perceived as a call for return to the old order. Advances in communications and reporting have only served to solidify this principle. The Reagan administration argues that the rebels in the north of Nicaragua are not correctly characterized as ex-Somocistas, but whether it is fact or fiction they are generally perceived to be sympathetic to the former Somoza regime.

2. A covert action is counterproductive.

The opponents of the Nicaraguan government within Nicaragua will not be able to make much headway as long as the Sandinistas can rally the people behind fear of "the devil to the north." The Sandinistas now rationalize their progressively pro-Cuban orientation and their suppression of freedoms at home as necessary responses to "Yankee imperialism." This is one reason that the Nicaraguan church, the private sector and other democratic elements have urged that covert action be stopped. These Nicaraguans need to prove that opposition to the Sandinistas does not entail the return of the Somocistas. 3. Even if a covert action succeeds, the gain to the United States is uncertain.

By toppling the Sandinistas and installing the rebels, we would thwart Cuban and Soviet short-term plans for Nicaragua, to be sure, but how durable would be a government built on the reassembled remnants of a military organization the Nicaraguan people themselves smashed and expelled from the country just a few years ago? Is it really plausible to believe that such a government would have or eventually could win the trust and allegiance of the Nicaraguan people? The presumption is against a policy that ignores the principles of self-determination and national sovereignty.

The uncertain value of success raises a further question about the policy behind a covert action. The basic sources of insecurity in Central America are mainly internal, socioeconomic ones. The external sources of instability, while important, exist in large measure because of the internal ones. Since the reported covert action has now become highly visible, it conveys the impression that the United States is concentrating its primary attention in the region on a military response to the spread of communism, not on measures to deal with social inequality and economic deprivation. But if the United States appears to be preoccupied, and ultimately is preoccupied, with the military response alone, it will not solve the underlying problems of the region and will not check the advance of communism in the long run.

4. A covert action risks a wider war.

One risk is that limited intervention suddenly might spiral out of control. Covert action on behalf of Nicaraguan insurgents is difficult to control because the insurgents' purposes are not ours. Another risk is trouble with Honduras. The Nicaraguan people are now hearing of five to 20 deaths on their northern border every day. At some point, pressure to take direct military action against Honduras might become too strong to contain. Either of these developments might be followed by a Nicaraguan call for more Cuban and Soviet military aid, and possibly for Cuban military units. This in turn could provoke a vigorous American response. A major war on Central American soil would be a calamity for victor and vanquished alike.

5. A covert action makes it more difficult for the United States to support regional initiatives whose aim is to secure a negotiated peace and a withdrawal of foreign military advisers.

In January, Colombia, Mexico, Panama and Venezuela met and issued a document that called for "putting an end to the support . . . of former Somoza guards." These countries deliberately failed to invite the United States, a nation whose apparent commitment to a military solution undercuts their search for a political solution. The United States has a long history of military involvement in Central America, and many of its Latin American friends see the reported covert action as another example of interventionism. They wonder how the United States can reconcile it with its claims to favor dialogue with Nicaragua.

6. The ramifications of a covert action outside the region are disturbing as well.

The Soviets have been handed a propaganda advantage, which they will use against the United States in the battle for the "hearts and minds" of Europe. Already when Americans talk about Poland and Eastern Europe, Europeans talk about Nicaragua and Central America. France, Spain and Greece have condemned covert action outright. The advantage ceded to the Soviets is evident at the United Nations and among the nonaligned countries.

The reported covert action, widely acknowledged but officially denied, holds the American government up to ridicule and charges of official deception. It makes the legitimate covert activity of the Central Intelligence Agency more difficult to carry out, and it saps public confidence in the agency.