TEGUCIGALPA, HONDURAS, SEPT. 18 -- Nicaraguan rebels today released 80 Sandinista prisoners and flew them to Costa Rica in what the rebels called a humanitarian act to demonstrate compliance with a Central American peace plan.

{After their arrival in the northern Costa Rican town of Liberia, the released prisoners were asked if they wanted to return to Nicaragua, remain in Costa Rica or travel to a third country. Only 20 of the former prisoners crossed the border into Nicaragua this evening, however, and they were met by Sandinista military authorities, Washington Post correspondent Julia Preston reported from the Nicaraguan side of the border crossing near Liberia.}

The Nicaraguan Resistance, a political umbrella group of the rebels, known as counterrevolutionaries or contras, said in a statement that the release showed the rebels' "respect for human rights" and their "political will" to comply with a Central American peace accord signed Aug. 7. The agreement, signed by the presidents of Nicaragua, Costa Rica, Guatemala, El Salvador and Honduras, calls for the release of prisoners held by insurgent groups in conjunction with government amnesties for the rebels to be declared by Nov. 7.

Although the contra political leadership has said it was prepared to accept the regional peace plan, today's prisoner release was the first tangible sign that the rebels intend to abide by its terms and test the willingness of the Sandinista government to do the same.

Contra officials said some of the prisoners had previously indicated a desire to remain with the contras or continue to live in Honduras, but the officials declined to specify how many had made such a decision.

A contra military spokesman, Bosco Matamoros, said the rebels intend to release all their prisoners, but that some could not be accommodated on today's flight. He said that "about 20" remained in the rebels' custody and would be released soon.

Although Matamoros insisted that the release was a "unilateral action" unrelated to developments in Managua, the release was seen here as the latest move in a game of one-upsmanship currently being played out between the rebels and the Sandinistas to show compliance with the peace agreement. The contras now are expected to demand that the Sandinistas reciprocate by releasing all accused "counterrevolutionary" prisoners jailed in Nicaragua.

The Sandinista government says it holds about 4,000 "counterrevolutionary" prisoners, including about 2,300 members of the disbanded National Guard who have been held since the Sandinistas took power in 1979. The contras said that up to 10,000 political prisoners are held in Sandinista jails.

The Sandinistas this month released 16 prisoners as part of an effort to show compliance with the peace accord.

{In Managua, the foreign ministers of the five Central American nations ended a two-day meeting called to work out details of the peace plan.}

The prisoners -- 78 men and two women -- some of whom have been held since 1984 at rebel bases along the Honduran border with Nicaragua, were taken to the central Honduran air base of Aguacate and flown aboard a contra DC6 on a circuitous route to Liberia.

Among those being released, according to a copy of the list, were at least 21 persons described as Sandinista infiltrators who had joined contra forces as spies and saboteurs. According to Matamoros, two of them, Mario Aristides Rosales Jarquin, a 2nd lieutenant in the Sandinista state security force, and Alexander Danilo Chavarria Morales, who managed to penetrate the contras' "strategic command" headquarters in southern Honduras, had been ordered to assassinate contra military commander Enrique Bermudez.

Matamoros said Chavarria Morales had told interrogators that although he eventually met Bermudez, he did not attempt to kill the former Nicaraguan National Guard colonel because he became disillusioned with the Sandinista regime.

Another soldier freed was Richard Lugo, the 18-year-old son of a senior Sandinista Navy officer.

The contras had tried unsuccessfully to trade him for contra prisoners held by the Sandinistas, but the Managua government has consistently refused to negotiate any prisoner exchange with the rebels.

According to reports from Costa Rica, 16 Nicaraguan students, out of 80 who attended Central American independence day ceremonies Sept. 15 on the border between Nicaragua and Costa Rica, refused to return to their country.