Central American tug of war

Nicaragua and Costa Rica have agreed to tighten security on their borders, but there is uncertainty on both sides that the move will prevent Costa Rica-based rebels from stepping up attacks inside Nicaragua.

Relations between the two Central American nations have deteriorated - with Nicaragua worried that Costa Rica is providing anti-Sandinista rebels with a strong base of operation, and with Costa Ricans concerned that their country could be dragged into Nicaragua's guerrilla conflict.

Influential leaders in Costa Rica's ruling National Liberation Party are putting pressure on President Luis Alberto Monge to take a more neutral, evenhanded position toward Nicaragua. This pressure so far appears to be having at least a limited effect.

One result of this pressure appears to have produced Costa Rica's agreement to meet with Nicaraguan officials in the Nicaraguan beach town of San Juan del Sur this week. A second meeting has been announced for April 14.

In addition to agreeing to tighten security on their borders, the two nations plan to reactivate a joint commission to deal with border disputes. Costa Rica, however, did not go so far as to accept Nicaragua's offer of a friendship treaty.

Costa Rican Foreign Minister Fernando Volio Jimenez reported that he had told the Nicaraguans that anti-Sandinista leader Eden Pastora Gomez had left Costa Rica and that Costa Rica would not allow him to return. Some Pastora colleagues in San Jose, the Costa Rican capital, say he has crossed into Nicaragua.

Nicaragua said that it will supply Costa Rica with intelligence reports on armed Nicaraguan exile groups operating in Costa Rica and that both sides had agreed to take steps to avoid intrusions into each other's territory by national military patrols.

Opinions on the results of this week's meeting varied widely. Costa Rica's ambassador to Nicaragua, Jesus Fernandez, praised ''the magnificent attitude of cooperation and mutual respect.'' But the Costa Rican foreign minister told reporters that ''from the results, I see nothing that will improve relations.''

In Nicaragua, the newspaper of the ruling Sandinista Liberation Front called the results ''extremely positive.'' But Army chief of staff Joachin Cuadra warned of rebel plans to ''open another front'' from Costa Rica.

Costa Rica had canceled a similar meeting last November after Nicaragua vehemently protested an attack on a border town by rightist guerrillas. Foreign Minister Volio says that of 86 protests by Nicaragua on counterrevolutionary activity supposedly related to rebels based in Costa Rica, six attacks could be confirmed.

At the San Juan del Sur meeting, Mr. Volio did not budge an inch on Nicaragua's insistence that it be allowed to inspect Costa Rican shipping on the the San Juan River, which forms the eastern half of the border between the two countries. The river belongs to Nicaragua, but treaties give Costa Rica navigation rights.

The Sandinistas have begun tight inspections of river traffic, searching for guerrillas, weapons, and ammunition. But Volio maintains the searches are a violation of Costa Rican sovereignty and cannot be further negotiated.

Volio and Costa Rican President Monge are hard-liners toward Nicaragua. Doves in their own National Liberation Party (PLN), including influential former Presidents Jose Figueres and Daniel Oduber and Security Minister Angel Edmundo Solano, are pressing for a more neutral stand.

Mr. Figueres, in particular, has worried that the nation's worsening relations with Nicaragua under President Monge and the government's apparent policy of looking the other way on the anti-Sandinista rebel groups inside its borders could be drawing Costa Rica into the Nicaraguan war. Increasingly, some PLN members are accusing the government of ''subservience'' to President Reagan's policies in Central America. They say it appears the United States is militarily backing anti-Sandinista rebels based in Honduras while using Costa Rica as a political base against the government in Nicaragua.

With US encouragement, Costa Rica last year organized the Central American Democratic Community, inviting elected governments in El Salvador, Honduras, and Belize, and leaving out Guatemala and Nicaragua. US Undersecretary of State for Inter-American Affairs Thomas Enders attended the group's only meeting.

This year, Costa Rica is trying to organize a summit with all Central American nations but excluding the US. No date has been set, and Nicaragua has not said whether it would attend.

In what may be a Central American version of the ''Radio Marti,'' a radio broadcast sponsored by the US and beamed at Cuba, the US reportedly intends to build a series of radio and TV transmitters in Costa Rica near Nicaragua.

Costa Rica, which confiscated control of the anti-Sandinista radio station Voz del Sandino in mid-February, returned it to the rebels in late March.

Although Costa Rica has agreed to tighten its borders, there is strong doubt here that it will be able to do an adequate job of patrolling the border region. It has trained only about 300 men to patrol the border, but officials here say it would take about 1,000 men to do a good job.

Tuesday, the Pentagon announced that 22 US Navy combat engineers are going to dig water wells in Guanacaste Province bordering Nicaragua and where the Costa Rican Civil Guard reports finding 17 abandoned camps of the counter-revolutionaries in the past year.