C. American peace bid. Tough negotiations lie ahead on regional plan to bring reprieve from civil wars

Like smoke from spent fireworks, euphoria still hangs in the air here after the signing of a historic peace agreement by five Central American Presidents. Although the accord is vague enough to accommodate many interpretations, analysts agree it represents a turning point in relations between the United States and Central America. Two years ago, the four US allies in the region - Guatemala, Costa Rica, Honduras, and El Salvador - were all stacked up against Nicaragua's Sandinista government. Since then, Guatemala and Costa Rica have pulled away from a pro-US stance. But last Friday's pact marks the first time that all four US allies have joined in an agreement that rebuffs official US policy. (US reaction: back page.)

As Central American diplomats turn their attention to the many obstacles remaining on the road toward a cease-fire, they are also reflecting on the rare confluence of forces that gave rise to the accord.

Such an independent agreement could never have been carved out, these diplomats say, were it not for two factors: the rising social costs of rebel wars in El Salvador and Nicaragua, which have recently heightened those countries' desire for peace; and the Reagan administration's eroding influence.

Under the terms of Friday's document, the US will have to suspend military aid to the Nicaraguan contra rebels after Nov. 7, 90 days after the agreement's signing. And the contras will no longer be allowed to use Honduras and Costa Rica as bases for launching offensives against Nicaragua's government.

The agreement will also make it more difficult for President Reagan to push through a request for more military aid to the contras, says one US Democratic congressional aide closely involved in the negotiations here. He explains that fewer Democrats are likely to ignore the pact, which is the first to be signed exclusively by Central Americans.

Indeed, the Presidents showed pride in their ability to reach an agreement on their own. ``We Central Americans understand the problems, and the answers to those problems, better than anyone else,'' said Costa Rica's Oscar Arias S'anchez. ``So we picked up the challenge. This is a Central American agreement.''

``We want to become the principal actor of our own history,'' added Guatemala's President, Vinicio Cerezo Ar'evalo. ``We're asking foreign nations to respect our own will to construct peace.''

The US, long a central actor in the region, almost stole the stage just two days before the Presidents met by offering a bipartisan peace proposal. The Central Americans firmly but politely pushed it aside and forged ahead with their own negotiations.

Ironically, the US plan may have served to jell a sense of regional identity and a desire to sign an accord. ``When the Reagan plan was made public, it provoked an anti-American reaction,'' a senior contra official lamented.

But what prodded accord this time, after repeated past failures, probably had less to do with pride than with the price of war in El Salvador and Nicaragua.

Both Daniel Ortega Saavedra of Nicaragua and Jos'e Napole'on Duarte of El Salvador made concessions which they had consistently refused earlier. Mr. Duarte, largely dependent on US aid, spurned the US's contra policy - so that other governments in the region would halt their support of Salvador's leftist insurgents. And in order to be able to revive Nicaragua's economy, Mr. Ortega accepted many internal reforms, including freedom of speech and the press, which might make his political foes more powerful.

Duarte ``has been very flexible - as has Ortega - because they are both quite desperate and they both want peace,'' Mr. Arias said. ``They know that if they are not flexible, if they don't compromise, the war would go on.'' [Reuters said yesterday that Nicaragua would withdraw a World Court case against Costa Rica as a gesture of ``fraternity.'' Nicaragua had accused Costa Rica of sheltering the contras.]

But such flexiblity may not be so apparent when it comes to negotiating a cease-fire - the litmus test for the plan's success.

The contras, though excluded by the accord from national dialogue to be held with the ``unarmed opposition,'' took some comfort in the vaguely worded cease-fire conditions. The agreement asks each government to take the ``necessary actions'' to reach a cease-fire. Contra leader Adolfo Calero insists that ``the cease-fire will have to be negotiated by us.'' A Sandinista adviser dismissed that contention. ``They are not players in the game. We'll deal directly with Washington.''

Even if the plan achieves its political aims, analysts say that conflict in Central America is likely to continue. For while the plan could give a reprieve from the economic consequences of war, it does not address the deeply rooted problems of economic stagnation and unequal distribution.

Central American peace-plan timetable 15 days from day of signing: The five foreign ministers will meet to discuss the mechanisms for:

Reaching goals of plan, including a cease-fire dialogue with unarmed opposition groups.

Political amnesty.

Cutoff of external aid to rebel forces.

Freedom of speech and the press, free elections, and verification measures.

Within 90 days of signing:

Cease-fire will be established simultaneously with the initiation of other requirements. Within 120 days:

A specially formed international commission will analyze the progress toward the completion of these agreements.

Within 150 days:

The five Presidents will review the commission's report and take further decisions.