Returning from Central America, I find people are interested not so much in how things go down there as how they go up here. Specifically, does the Reagan administration have a policy to achieve its goals of supporting friendly reformist governments and resisting communism? Can it get there from here?

To me it still seems possible, but the administration is edging along a narrow rail, and it could fall off at any of four points--El Salvador, Nicaragua, Cuba and the Soviet Union.

1)El Salvador.10 President Reagan appears deaf to the interest of the good civilians in exploring talks with the other side after the March 28 elections. (This assumes President Jos,e Napoleon Duarte comes out well; if Roberto D'Aubuisson of the hard-core right prevails, Congress may be forced to conclude we lack the worthy local partner we need to pursue our interests.) Currently Duarte serves at the pleasure of the generals and, at their nod, dismisses "negotiations." With a popular base of his own, he could move toward the "dialogue" he long has sought.

Will the administration give him the requisite support--by laying down the law to the armed forces? Informed Salvadorans pick up signals that, for some in Washington, Duarte is too much of the left. There is a grim hint that the military way, including support of reforms, is the only way, and that "our" Salvadorans, or the American public, would wilt in a negotiation. This means fighting to the last Salvadoran.

2)Nicaragua.10 The choice is whether to accept the Sandinista revolution and work to sustain its pluralistic element, or to try to bring down that regime. It is conceivable--to Sandinistas it is a certainty--that a quiet decision has already been taken to follow the latter course. This would indicate a policy of destabilization and intervention, behind a facade of negotiations, and it will almost certainly crash.

For the Sandinistas are not the isolated leftist apparatchiks and street fighters who were swept out in Chile's anti-Allende coup of 1973. They are tough cookies, holding all their country's guns, capable of mobilizing Nicaraguan nationalism, with useful kinds of foreign support close by. It is dreaming to think their rule will be altered by any but political means, unless the United States itself directly intervenes --I cannot believe that will happen.

It is completely wrongheaded for the president to toy with a covert option. That lets the Sandinistas wave the national flag, invites them to tighten their repression and to become more dependent on Cuba, and denies the United States the essential tactic of going to the Organization of American States (and the American public) to demand that Nicaragua leave Salvador alone.

The idea that we can trade the fact or hint of our covert action in Nicaragua against theirs in El Salvador is grade- school politics. Against their subversion we have a better card: accepting Nicaragua's internal disposition as, Harvard's Jorge Dominguez reminds us, we accepted Mexico's earlier in the century on the basis of its tacit forswearing of alignment with an outside power.

3)Cuba.10 With Mexico's help, the United States has begun "going to the source" diplomatically--opening an exchange with Cuba. As in the exchange begun with Nicaragua last year, it may not yet rate the label of negotiation. Not only is it hard to tell whether the administration is doing more than trying to calm its domestic and international critics. The administration may not have decided whether negotiations can help it or hurt it in a substantive sense.

It seems unlikely that the administration will get far soon by putting its whole relationship with Cuba on the table, if that's what it's up to. That relationship is awfully dense, and it is drenched in a heavy history. But it would surely be of value to start work with Cuba on a hemispheric agenda. The trick is not to bite off too much with Havana, or too little.

4)Soviet Union.10 It strains the imagination to see why we would want to put much emphasis on the Soviet contribution to our Central American frustration. To inscribe El Salvador on the Soviet-American agenda is to get into an area of sticky great-power tradeoffs and to diminish even further the central attention due to the conflict's local origins. Moscow is a party, but it is a party of the fourth part-- after El Salvador, Nicaragua and Cuba.

As for making Moscow pay for its indirect encouragement of Salvadoran revolution, we have our hands full now trying to make Moscow pay for its direct depredations in Afghanistan and Poland. Let's just cool this one.