Why US might snap Mexico's Salvadoran olive branch

Mexico is putting unprecedented energy into promoting the peace proposals for Central America it first made public last month.

If nothing else, the proposals presented to US Secretary of State Alexander M. Haig Jr. seem to indicate that Mexico is now prepared to play a major diplomatic role as an arbiter among the contending forces in Central America.

State Department protests to the contrary, however, US and Mexican analyses of what is happening in Central America seem to diverge in fundamental ways. Thus, the chances for a US-Mexican accord on how to deal with El Salvador and the troubled region surrounding it are still rated as slim. But the State Department is carefully studying the Mexican proposals.

One Latin American specialist says that the Mexicans' unprecedented push to promote the proposals -- first made public in Managua, Nicaragua, by President Jose Lopez Portillo -- is based to a degree on a pessimistic appraisal of the situation in El Salvador.

''The Mexicans think that the military situation is deteriorating so rapidly in El Salvador that the US is going to be tempted to undertake a major escalation,'' says this specialist. ''The Mexicans are convinced this may be the last chance for a negotiated settlement.''

On March 6, Mr. Haig met in New York with Mexico's foreign minister, Jorge Castaneda de la Rosa, to discuss the Mexican plan. But Haig made it clear that, in the US view, the essential element missing from the Mexican proposals was a provision dealing explicitly with Nicaragua's supply of arms to Salvadoran guerrillas.

For his part, Castenada said that Mexico believed that the amount of arms supplied by Nicaragua to the guerrillas was limited. He also said the flow of such arms could perhaps be halted if the Reagan administration made peaceful gestures toward Nicaragua.

Mexico's proposals call for a negotiated settlement of the fighting in El Salvador, for a non-aggression pact between the US and Nicaragua, and for talks between the US and Cuba designed to produce mutual concessions in the region.

The US has been calling for a settlement in El Salvador within the context of the forthcoming elections there. But Castenada dismissed the elections as meaningless, given the absence of candidates from among the guerrilla forces.

Mexico might be in a position to mediate the Salvadoran conflict because it maintains good relations with Cuba, Nicaragua, and with representatives of the Salvadoran guerrillas. It has special ties with anticommunist governments in the region through concessionary sales of Mexican oil.

In a paper concerning US and Mexican policies toward Central America, Robert L. Ayres and Cathryn Thorup of the Overseas Development Council stated that the US and Mexico have until now ''agreed to disagree'' about Central America.

As authors describe it, the two countries hold ''sharply contrasting perceptions'' of the nature of the crisis in Central America. The White House views Central America as a ''pawn'' in a global East-West power struggle. The Mexicans, according to the authors, think that outside powers are only exploiting a situation whose underlying causes reside in ''economic and social inequalities accompanied by . . . ruthless military suppression of dissidence.''