Contra groups meet in Costa Rica in attempt to reform, unite. But talks this week stall on issue of sharing power

Faced with serious questions about its credibility, the Nicaraguan contra rebel movement is urgently seeking a way to reform itself politically. This week in Costa Rica, major contra groups agreed generally on reforms to unify the splintered movement into a single, more broadly democratic organization.

But the talks stalled over the particulars of power sharing, leaving the contra movement stranded in distrust and factionalism.

Leaders of the main contra umbrella organization, the United Nicaraguan Opposition (UNO), say they are close to reaching an accord with the Costa Rican-based rebels of the Southern Opposition Bloc (BOS) and with the Miskito Indians on Nicaragua's Caribbean coast. The accord would unite the contras into a single political and military organization.

The talks have been briefly suspended, they say, to allow negotiators to consult their supporters.

But BOS director 'Alvaro J'erez says the negotiations are over. He charges that UNO negotiators are trying to design the new organization in such a way that assures them control of the staff.

Yet Mr. J'erez admits that without unity, the contra movement has no chance of succeeding. He claims to be looking for support among UNO members.

Even if the talks fail to unite the factions, says UNO secretary-general Leonardo Somarriba, UNO will reorganize along the lines promoted by moderate UNO director Arturo Cruz before he resigned earlier this month.

A key change envisaged by UNO leaders is the gradual conversion of the Honduran-based Nicaraguan Democratic Force (FDN), the largest contra army, into a force supplied and directed entirely by civilian directors.

The new directorate is widely expected to include the return of former UNO director Adolfo Calero, the FDN political chief, who resigned from the UNO directorate in February. Most contra leaders agree that an FDN member on the directorate is necessary, if there is to be political control over the army.

This arrangement reportedly has the blessing of Col. Enrique Berm'udez, the FDN's field commander, as well as of Mr. Calero.

Miskito Indian leader Brooklyn Rivera and BOS have also agreed to this military arrangement. But BOS and Rivera's Miskito Indian rebel organization, the Misurasata, disagree with UNO over the makeup of the expanded rebel assembly and its directors. To BOS's J'erez, UNO, and especially its secretary-general Somarriba, are tainted by close cooperation with the United States Central Intelligence Agency.

UNO finds it important to unite with BOS and the Misurasata because (1) BOS, although small, has credibility in some Latin American countries and in European social democratic circles, credibility that UNO does not have, and (2) Rivera's Misurasata could command significant numbers of supporters in eastern Nicaragua.

It will be hard to convince many US congressmen that contra changes are more than cosmetic, says Victor Johnson of Inter-American Dialogue, who was a House staff aide on the contra issue until recently. ``People take a very jaundiced view of this sort of thing. We've seen it before.''

Robert Leiken, a close contra watcher who now writes for the New Republic, a liberal weekly magazine, sees the effort to unify and reform the movement as a serious one, but says it has probably failed. ``My sense is that things right now are in disarray and that nothing is happening.''

Even as the talks were stalling in Costa Rica this week, another contra faction split away. Fernando Chamorro pulled his estimated 500 Costa Rican-based troops out of UNO this week because, he said, the organization was run by ``opportunists.'' Mr. Chamorro had tentatively withdrawn from UNO in January.

The contra leadership's credibility crisis has been growing for months. Tainted by the scandal over funds diverted from arms sales to Iran, unable to show progress on the battlefield, accused of committing atrocities against Nicaraguan civilians, and unable to account for millions of dollars in US aid, the contra leadership began unraveling in January.

Contra groups BOS: Southern Opposition Bloc. A Costa Rican-based political organization that considers itself social democratic. It commands only a handful of troops. FDN: Nicaraguan Democratic Force. The main contra military group, based in Honduras and made up of an estimated 10,000 to 12,000 men. UNO: United Nicaraguan Opposition. The main contra umbrella organization formed in June 1985 by the Reagan administration. Misurasata: A Miskito Indian political-military group, which refused to join UNO. It has an estimated 1,000 guerrillas.