MANAGUA, Nicaragua (AP) _ Four prominent opposition leaders, named by the government as suspects in an alleged CIA conspiracy, have been detained by security agents, witnesses and relatives said Saturday.

The Interior Ministry confirmed the arrests of Alberto Saborio, president of the Nicaraguan Bar Association, and Mario Rappaccioli, vice president of the Nicaraguan Democratic Coordinate, the nation's main opposition group.

Other sources said Julio Icaza Tijerino,68, a lawyer and a member of the Conservative Party, and Duilio Baltodano of the Social Christian Party also o, about 46, was picked up by agents.

All four men had been in Guatemala earlier in the week to meet with leaders of the Nicaraguan Resistance, an umbrella organization of U.S.-backed rebel groups fighting the left-wing Sandinista government.

The arrests came as the five Central American presidents were meeting in San Jose, Costa Rica, to discuss obstacles to a regional peace plan.

On Thursday, the Interior Ministry said 11 opposition political leaders were under investigation for possible roles in a plan ''produced by the CIA ... to cause conspiratorial and terrorist actions'' against the Nicaraguan government.

The four detained were among the 11 named.

Ana Cecilia Villa, an employee at the Rappaccioli home in Managua, said Rappaccioli left with four security agents who appeared Friday evening at his home and one showed him a document.

Patricia Rocha, who lives next to the Saborio hourse in Managua, said Saborio was taken away by agents Saturday morning.

Rappaccioli, a 59-year-old businessman, and Saborio, 50, are members of factions of the Conservative Party.

Interior Minister Tomas Borge said Friday the fate of the 11 suspects would depend on ''the depth of the investigations.''

In addition to the four detained, those under investigation were identified as Agustin Jarquin of the Social Christian Party; Carlos Huembes, president of the Democratic Coordinate; Miryam Arguello of the Conservative Party; Jaime Chamorro, co-owner of the opposition newspaper La Prensa, and Tomasa del Rosario Hernandes, Cairo Manuel Lopez and Edmundo Henry Pallais, all members of opposition parties.