An effort this summer to unite all Nicaraguan Indian groups battling the Sandinista government appears to be foundering because of mistrust between the two largest Indian organizations.

One of the two major Indian rebel groups, called Misura, said today that the other group's leader, Brooklyn Rivera, had been expelled from the Indian movement as a whole. A tribal council of elders, which is linked to Misura, expelled Rivera about a week ago because he was considered a traitor for having held peace talks with the Sandinistas, Misura officials Roger Hermann and Adan Artola said.

Rivera does not recognize the council's authority, and he still is trying to reach an understanding with Misura, a spokesman for Rivera said. But the dispute seemed to signal that the unification plans were headed for failure and that Misura and Rivera's organization would continue to struggle independently to achieve autonomy for the Indian region on Nicaragua's eastern coast.

The persistent division in the Indian movement was likely to please the Sandinista government, which has been trying to reach a separate peace with Rivera. Plans were made in June to unify the Indian movement after Rivera broke off his negotiations with the Sandinistas to protest their unilaterally forming a commission to consider how to grant the Indians a measure of self-government.

In a separate development, Honduran officials said today that they expected that Misura's former military chief, Steadman Fagoth, would be deported from Honduras. The Honduran Army detained Fagoth, one of the Indians' best known leaders, on Aug. 10, immediately after Fagoth took a group of Indian leaders as hostages for two days in an abortive effort to regain control of Misura.

Fagoth and about 30 supporters took 12 Indian leaders and guerrillas as hostages just inside Nicaragua near the town of Waspuk on Aug. 8, the two Misura officials said.

Other Misura military leaders refused to back down, however, and Fagoth gave up and fled across the border to Honduras, the officals said.

The Honduran Army detained Fagoth at a base in the northeastern town of Mocoron on the ground that he was not supposed to be in the country. Fagoth technically has been barred from entering Honduras since January, when Honduran authorities deported him after he embarrassed the government by saying at a news conference in Honduran territory that Misura intended to execute 23 prisoners.

The Misura officials said that Fagoth also had been expelled from the Indian movement, together with Rivera, for having taken the hostages. Fagoth was Misura's military chief of staff from 1982 until he was demoted last March.

The Miskito, Sumo and Rama Indians live on Nicaragua's Caribbean coast, where they are isolated from the majority of the country's population living in the highlands along the Pacific Coast.

The Indians generally supported the 1979 Sandinista revolution against the Somoza family dictatorship, but many Indians later turned against the Sandinistas because the new government was unwilling to grant autonomy to the region. The Sandinistas also alienated the Indians by forcibly moving thousands of them from their villages in 1981.

The Indians launched a guerrilla movement to fight the government, but it split in 1982 into two main groups. These were Misura, headed by Fagoth and based along the northeastern border with Honduras, and Misurasata, headed by Rivera and based along the southeastern Costa Rican frontier.

At a meeting in Miami on June 19, the two main groups and several smaller ones agreed in principle to merge into a single organization. They acted in part because the Sandinistas were moving ahead on their own to develop an autonomy plan for the region, and the Indians wanted to present a united front in opposing it.

The merger was supposed to be ratified at an assembly of Indian leaders and village representatives to be held no later than Aug. 16, but that meeting already has been postponed twice. Now Misura plans to hold the assembly on Friday and Saturday, apparently without Rivera, who is pressing for another postponement.

Now that Fagoth seems to have been ousted, Misura's new top leader is expected to become longtime Indian leader Wycliffe Diego, the two Misura officials said. Another Indian leader, Raul Tobias, is serving as Misura's chief of staff.