This week's agreement between Nicaragua and Costa Rica to revive efforts to prevent armed clashes along their border could not have come at a more opportune moment for Nicaragua. With President Reagan asking the United States Congress for $100 million to support the left-wing rebel war against Nicaragua's ruling Sandinistas, any steps taken locally to cool regional conflicts put the US in the role of a ``spoiler,'' say analysts here.
The decision to set up a bilateral ``inspection and vigilance commission'' for the border suits the goal of Costa Rican President Luis Alberto Monge: To leave his successor with as few problems as possible when Mr. Monge completes his term in May.
But, in the light of past failures to control the border, the vagueness of the terms of Monday's accord leaves room for doubt as to its effectiveness.
The nearly 200-mile Nicaraguan-Costa Rican border, much of it running through inaccessible forests, has been the scene of regular clashes between Sandinista forces and the rebels -- known as ``contras'' -- for the past four years. Most of the contras here follow Eden Pastora's ``Democratic Revolutionary Alliance.'' The group is widely believed to have established its base camp on the Costa Rican side of the San Juan River, which marks the frontier. Costa Rica denies this.
An earlier bilateral commission, set up in 1984 to control the border, proved ineffectual because it could only investigate complaints of violations by both sides after a clash occurred.
The commission had collapsed by the time two Costa Rican civil guardsmen were killed last May while patroling near the Nicaraguan border. Costa Rica blamed the incident on Nicaragua. Nicaragua blamed the contras.
The Sandinistas acknowledged earlier this month that the guardsmen had died during a cross-border fire fight between Nicaraguan troops and contras. This proved sufficient to prompt President Monge to reestablish normal diplomatic relations, sending his ambassador back to Managua after an eight-month absence.
That move, followed by Monday's meeting between Nicaraguan Deputy Foreign Minister Victor Tinoco and his Costa Rican counterpart, Gerardo Trejos, clearly smooths the path for incoming Costa Rican President Oscar Arias S'anchez, who will take office on May 8.
Mr. Monge seems determined, Western diplomats in San Jos'e say, to leave Mr. Arias a clean slate on which to write his own policy toward the Sandinistas.
The Sandinistas view the accord as ``a reminder to the US government that it should accept peace,'' said Nicaraguan President Daniel Ortega Saa-vedra after Monday's meeting. ``We are showing once again that there is a desire for peace among Central Americans.''
As the US Congress prepares to debate Reagan's request for renewed military aid to the contras, Managua sees the deal with Costa Rica as a timely rejoinder that countries in region can solve their problems on their own. The accord reinforces Managua's attempts to sort out problems individually with its neighbors within an overall bid, led by what is known as the Contadora group, to reach a regional peace treaty.
The presence of deputy foreign ministers from four Contadora members, Mexico, Venezuela, Panama, and Colombia, at the meeting seemed to give a blessing to this approach. While supporting Contadora's initiative, Managua has been frustrated when dealing jointly with Honduras, El Salvador, and Costa Rica, all close US allies that have often opposed Sandinista proposals.
Another meeting has been fixed for March 12 to discuss further the nature of the ``inspection commission,'' which is expected to be made up of civilians and military experts acting as observers at the border. This goes well beyond the mandate given to the last border commission, but falls short of Nicaragua's hopes of creating a demilitarized zone along the frontier. Costa Rica has refused to accept this proposal, arguing that as a country without an army, it does not have sufficient troops to help patrol such a zone.