Sandinista and Contra negotiators are heading back to the bargaining table to determine the areas where rebel fighters will gather during the cease-fire called for in the accord signed last week.

The talks, scheduled for Monday in the southern outpost of Sapoa, also may consider the issue of when the U.S.-supported Contras lay down their arms.On Sunday, the leftist Sandinista government fulfilled the first part of the cease-fire accord by freeing 100 political prisoners under an amnesty program. Most of them are accused of being Contra rebels.

Afterward, Interior Minister Tomas Borge called the amnesty "possibly the beginning of the end of the (6-year-old) war," and he called for the Contras to release Nicaraguan peasants its troops had kidnapped.

After celebrating Palm Sunday Mass, Roman Catholic Cardinal Miguel Obando y Bravo called the prisoner release "very positive."

However, during his homily the Managua archbishop warned that the cease-fire agreement did not mean that "we have already reached peace."

"Let us not make a mistake," he told his parishioners. "Let us not confuse ourselves. They have only signed a cease-fire," he said, emphasizing the point by repeating the last sentence three times.

It was in Sapoa where leaders of the Contra umbrella organization, the Nicaraguan Resistance, met with the Sandinistas last week and agreed on a 60-day cease-fire beginning April 1. Further high-level negotiations are tentatively scheduled for April 6 in Managua to reach a more permanent truce.

No fighting between Sandinista and Contra forces has been reported since both sides signed the accord in Sapoa on the night of March 23.

Maj. Gen. Joaquin Cuadra, deputy defense minister and chief of staff of the Sandinista army, was to head the government delegation at Monday's talks. Deputy Foreign Minister Victor Hugo Tinoco and military intelligence chief Maj. Ricardo Wheelock Roman were to accompany Cuadra.

Under the Sapoa agreement, rebel forces are to gather without interference from Sandinista forces in specified zones inside Nicaragua during the first two weeks of April. Monday's talks between special commissions of the two sides were to define "the localization, size and modus operandi" of those zones, according to the text of the Sapoa accord.

Nothing is said in the Sapoa agreement about the Contras laying down their arms, and this may be taken up Monday as well. In past talks, the rebels insisted on keeping their weapons until all provisions of an accord were carried out.

Once rebel fighters have moved into the truce zones, the Contra leadership can send up to eight delegates to participate in the first national reconciliation talks on April 6.

Last week's pact provides a gradual amnesty for Nicaragua's 3,300 political prisoners; guarantees freedom of expression, which the rebels had demanded; and permits all exiles to return home and participate in the political process.

If the peace plan is carried out, Nicaragua could become the first Central American nation other than Costa Rica to fully comply with the Central American peace plan signed Aug. 7 by the region's five presidents.