WHAT is behind the extraordinary effort the president and his chief aides are making to win congressional and public approval for their Nicaragua policy? It almost seems as though the adminstration had been seized by its own kind of "liberation theology," a passionate but studied striving, both geopolitcal and moralistic in content, to translate its deepest ideals into political reality. Prudence may limit a direct application of this creed in places where communism -- the enemy of freedom that the administration is readiest to attack -- has been long ensconced. But in places where its presence is new or its roots are relatively shallow, the administration is pressing with extraordinary vigor to prevent new growth and to reverse what growth has taken place so far.

The working premise appears to be that it is worth the difficulty and criticism to move now in places such as Afghanistian and, above all, Nicaragua rather than to stand on diplomatic ceremony and watch the local regimes snuff out liberty at their convenience and become, by result if not design, pawns of Soviet power. This is the view that sees the hinge event of the last generation as the Bay of Pigs operation, where, in this view, the chance existed to block the consolidation of communist rule in Cuba, but the chance disappeared when an American president lost his nerve. For this lapse, the country has since paid many times over. There is reason to believe that such a Bay of Pigs syndrome explains the otherwise outlandish exulting tone in which the administration congratulated itself for its intervention in Grenada -- a battle of such unequal odds that a self-respecting great power would otherwise speak of it only in a very modest way.

In respect to Nicaragua, however, the evidence is that the administration's "liberation theology" is not held with equal fervor, or interpreted with equal literalness, in all quarters. At least three tendencies are visible beneath the facade of official consensus. One tendency, evident in some parts of the Pentagon, says go, go now, seize the moment of the fresh Reagan mandate to back the contras to the hilt, to apply pressure on Nicaragua's borders by constantly building maneuvers, to push American military support operations right to the verge of direct intervention, and to leave open and threatening the possibility of committing American forces.

The second tendency, apparent in the speechs of Secretary of Defense Weinberger and in hints from the Joint Chiefs of Staff, hesitates at the thought of committing American forces, but accepts the full range of other pressures now being mobilized against the Sandinistas. The hope here is that these pressures will either ignite further popular resistance within Nicaragua or break the spirit of the Sandinistas, in either event avoiding the sort of direct American role that would be uncertain and protracted (Nicaragua isn't Grenada) and controversial and might tend to curdle some of the public's taste for this group's No. 1 priority, the American military buildup.

A third tendency, not strong at the moment but biding its time for better days, holds that the essential thing is to stay alert to possibilities for converting military pressures into political accommodation, possibly with the help of Latin mediators. But regrettably, the negotiation circuit is down right now; the mediating efforts of several Latin American countries are in suspension, and the United States has broken off its bilateral talks with Managua. The State Department is the natural home for this tendency, although Secretary of State Shultz does not seem very hospitable to it these days.

And where does president Reagan stand? By his public statements he seems all but ready to swinginto the saddle and charge up the Nicaraguan equivalent of San Juan Hill. He is putting aside all of the grays in Nicaragua -- for example, the existence still of a limited legal opposition, a popular fighting church and a substantial private sector. He is putting aside the fact that some few but important elements of the "freedom fighters" he lavishly praises are ex-Somoza henchmen who still act the part. He is putting aside the fact that, because of past American interventions in Nicaragua, his current policy stirs the nationalistic opposition of many patriotic Nicaraguans and separates us from most of our friends in the hemisphere -- including friends who regard the Sandinistas with a very beady eye.

Mr. Reagan is talking very tough -- to intimidate the Sandinistas and perhaps also to appease those people in his administration and constituency who favor military action. There is a real risk, however, that his talk will somehow be taken as authorization for certain adventurous steps that in fact he has not specifically decided on. Presidents have gotten in trouble before for seeming to give a green light for drastic actions they came to regret. Mr. Reagan, it seems to us, has a real interest in throttling back his expressions of boundless faith in an American political "liberation theology" in order to make sure he does not wake up some morning and find that his choices have suddenly become even starker than they are today.