A MILITARY response is necessary in El Salvador, where a Nicaraguan-, Cuban-, Soviet-supported insurgency is attempting to overthrow an army-backed center-right government with a commitment to social reform. But a political response is necessary, too. It has not been in sufficient evidence as the Reagan administration cranks up to make El Salvador a demonstration of its worldwide anti-communist strategy.

A political response means two things. The Salvadoran government must show itself as eager to halt violence directed against civilians by soldiers and the right-wing death squads (often the same people) as it is to halt violence conducted by guerrillas. Precisely here lies the importance of keeping the heat on the government to discover who killed the American church workers. This incident cannot be parked in a "human rights" cubbyhole. It is, for many Salvadorans the test of whether their government if on their side. The United States would not want to help the government reduce the guerrilas, as could yet happen, only to find that the government's failure to rein in its own forces still denied it broad popular support.

The other requirement is to construct a negotiating framework, of which nothing has so far been heard from Reagan officials. Among the guerrillas and their civilian supporters, some are committed to armed struggle to the poing of regarding compromise as betrayal of their revolution.But other appear to be more conciliatory. The code word "Zimbabwe," meaning talks by opposing forces in a civil war, is gaining a certain currency. The United States may not have the sole duty, or the best opening, to promote negotiations. Mexico, for instance, seems better placed, if it could break through its revolutionary rhetoric and try. Other international parties are standing by. But the American interest in negotiations must be asserted.

There is an undeniable military dimension to the El Salvador crisis, but the crisis remains essentially political. The administration should not oversell the notion that a military showdown, launched essentially for considerations of Americans global strategy, is everything. Its best chance of being successful and supported in the policy it is now unveiling is to show itself open to the political dimension as well.