C. American pact unravels amid broken promises. A year after the ebullient signing of a peace plan, Central American hopes are dim. Not a single nation has reached a pact with armed rebels. The plan's survival hinges on renewed cease-fire talks in Nicaragua.

On August 7th, 1987, five Central American Presidents joined forces like the facets of a prism, focusing a single beam of peace on the troubled region. But one year after that magical convergence of disparate political desires into an historic regional treaty, the image of peace in Central America is blurred and fractured.

Not one country has shown the political capacity or will to fully comply with the plan's provisions to end guerrilla wars and ensure democratic freedom. And for those governments that have carried out parts of the pact, compliance seems designed to undercut their enemies rather than seek reconciliation.

After a year of broken promises, foiled hopes, and continued violence, the peace plan is in danger of falling part, according to Central American and United States officials.

The accord has already been unraveled by mounting internal crisis in each country, the lack of superpower cooperation, and - most important - the absence of forceful sanctions to ensure compliance.

``We cannot be entirely satisfied with what we have achieved,'' says Costa Rican President Oscar Arias S'anchez, who won the 1987 Nobel Peace Prize for his promotion of the Guatemala peace accords. ``But the alternative to these failures is not war. Our only choice is to keep trying to put the necessary pressure on the Sandinistas and on other countries as well for negotiations to be reestablished.''

The plan's survival now depends on reviving cease-fire talks between the Nicaraguan government and the US-backed rebels. For, as efforts to end guerrilla wars in Guatemala and El Salvador have been all but neglected by those nations' leaders, the pact's scope has narrowed to internal democratization of Nicaragua's government.

The peace plan has had one major success: For the last five months, the guns in Nicaragua have been virtually silent. The peace plan, by offering an alternative to armed struggle, played a large role in cutting off the US military aid to the contra rebels in February and in framing the subsequent cease-fire agreement between the rebels and the government.

But negotiations were suspended in June amid mutual recriminations. And since then, the ruling Sandinistas have tightened their grip on power - among other things, arresting 44 opposition figures and shutting down the opposition media at the beginning of July.

The Sandinistas ``have unmasked themselves'' Mr. Arias says bitterly, and for that they ``should be punished.''

But aside from moral force and diplomatic persuasion, Arias has little leverage left to pressure Nicaragua to negotiate internal changes. In a scheduled meeting this week with Nicaraguan President Daniel Ortega Saavedra, the Costa Rican pacifist will likely request the release of the 44 opposition figures and the lifting of emergency measures as preconditions for future talks, according to a close adviser.

Claiming that Managua, instead of Washington, is now isolated in international circles, Arias says he will do anything he can to turn up Latin American diplomatic heat on the Sandinistas. But he stops short of calling for more economic sanctions and military threats.

``Arias has acheived his No. 1 goal of stopping the war in Nicaragua,'' says a non-US diplomat here. ``But in doing so, he has left himself no tools to reach his second goal of democracy and social justice. He said he would have other tools to use. But where are they?''

For the US administration, which continues to see the armed Nicaraguan resistance, the contras, as the most viable way to force changes on the Nicaraguan government, the peace plan's rejection of military might dealt a frustrating blow.

``It has worked without question to undercut the President's policy of military pressure through the resistance,'' the US ambassador to Costa said in an interview. ``For a peace process to produce democratization as well as a cease-fire in Nicaragua, there has got to be some pressure. ... [Arias] utterly rejects the use of force and we don't.''

Arias admits that diplomatic and moral pressure is limited, but he insists the military option is no alternative, especially not with the hawk currently at the helm of the contras, Col. Enrique Berm'udez. Arias argues that more contra military aid would only give the Sandinistas a better excuse to repress internal opposition. Says Arias adviser Guido Fern'andez: ``If Congress approves more military aid, then the chances for the peace plan's survival are very slim.''

The treaty's beneficial effect on the other Central American countries has been negligible. Deep-rooted guerrilla wars in Guatemala and El Salvador have only intensified in the past year, as neither the governments nor the leftist insurgents have been willing to negotiate their power. Perhaps the most lasting result can be seen in El Salvador where long-exiled leftist politicians now work openly and legally - but not safely.

By allowing more space to political opponents, the peace plan has also opened the door for greater instability. It has been indirectly blamed for a recent Guatemala coup attempt, violent anti-US protests in Honduras, and increased death-squad murders in El Salvador.

Even in Costa Rica, the most peaceful nation in the region, internal political crises - some stemming from the plan itself - have forced Arias to drastically reduce the time he devotes to regional peace.

Despite the extra pressure and constraints, Arias is now trying to quietly sustain the peace process - even if it seems a task suited for Sisyphus.

``The peace process is like pushing a rock up a hill,'' says a European ambassador here. ``As soon as you stop, it starts rolling backward. You have to keep inching forward.''