TEGUCIGALPA, HONDURAS, JUNE 13 -- A Central American summit conference planned for later this month to discuss a peace plan for the region has been postponed indefinitely amid diplomatic wrangling.

The summit meeting of the presidents of Costa Rica, Nicaragua, El Salvador, Honduras and Guatemala had been set for June 25-26 in Guatemala City, after a previous postponement, to negotiate an end to the region's guerrilla wars on the basis of a plan proposed earlier this year by Costa Rican President Oscar Arias Sanchez.

The postponement appeared to reflect continuing fundamental disagreements among the five countries over provisions of the plan, which calls for cease-fires with insurgent forces, negotiations between governments and civil opposition groups, a ban on foreign military aid and foreign bases and a timetable for internal "democratization" in Nicaragua.

The postponement was announced after a meeting here yesterday among President Jose Azcona and Foreign Ministers Carlos Lopez Contreras of Honduras and Rodrigo Madrigal Nieto of Costa Rica.

Lopez and Madrigal explained afterward that Salvadoran President Jose Napoleon Duarte had asked for the postponement, and Honduras and Costa Rica had agreed, because a preparatory meeting of Central American foreign ministers was canceled and Duarte had planned a European tour.

No new date for the summit was immediately set, although diplomats indicated that it could be held in late July or in August.

Foreign Ministry officials here denied that the postponement resulted from any entreaties by U.S. special envoy Philip Habib, who has just completed a tour of Honduras, Costa Rica, El Salvador and Guatemala. Habib's meetings with the presidents of those countries "had absolutely, absolutely nothing to do with" the decision, said Honduran Foreign Ministry spokesman Eugenio Castro.

Costa Rica's Madrigal acknowledged, however, that the United States opposed a provision in the Arias plan to suspend all foreign aid to insurgent groups. The Costa Rican vigorously defended the provision in a press conference yesterday.

Habib, who declined to talk to reporters, has been quoted here as having told Central American leaders that the United States fears the proposed peace accord would not sufficiently guarantee U.S. security interests.

According to Honduran officials, the summit began to fall apart after Guatemala and Nicaragua reneged on a commitment to attend a foreign ministers' preparatory meeting in Tela, Honduras, June 22-23. Instead, Guatemalan Foreign Minister Mario Quinonez invited his Nicaraguan counterpart, Miguel d'Escoto, for bilateral talks on the same date, the officials said. Honduras then canceled the meeting in Tela.

Citing the need for a preparatory meeting and a visit to Europe that he is planning, Duarte then asked for a postponement of the summit and offered to host one or more preparatory meetings on his return.

"It's better that we take our time and that there be at least four foreign ministers' meetings so they can polish up the document that the presidents are going to discuss," Duarte said in San Salvador. He added that Nicaragua had not made up its mind about the peace plan, but had issued "five statements on it, all of them contradictory."

Duarte is believed to face opposition to elements of the plan from the Salvadoran military, which is battling an eight-year-old insurgency.