SAN SALVADOR, JAN. 10 -- In a move that could be a prelude to an acrimonious Central American summit meeting, Nicaragua has charged that the U.S.-backed rebels' main radio station operates out of El Salvador, according to Salvadoran officials.

Nicaragua's accusation, made during the 21-hour visit of a commission monitoring the progress of a regional peace agreement, appeared to be retaliation for charges by the Salvadorans that the Sandinistas are supporting El Salvador's leftist guerrillas.

The Salvadoran government reportedly also was outraged when the commission cut off a presentation by a high-level government delegation after only 10 minutes, saying it was more interested in hearing the opposition.

Gen. Adolofo Blandon, chairman of El Salvador's joint chiefs of staff, said after meeting with the commission yesterday, that Nicaragua accused El Salvador of allowing Radio Liberacion, the contras' official radio, to operate out of El Salvador.

"We invited the commission right now to go to the place the radio is supposed to be, to inspect the area, but they said they could not," Blandon said.

The 15-member commission, made up of representatives of the United Nations, the Organization of American States and 13 Latin American nations, is charged with preparing a report on each nation's compliance, to be presented at a meeting Friday of five Central American presidents in Costa Rica.

The peace plan, signed Aug. 7, calls for full democratic rights in the region, an end to support for guerrillas and amnesty for prisoners.

El Salvador's President Jose Napoleon Duarte, a staunch U.S. ally, has said repeatedly he will denounce Nicaragua for not complying with the accord. Last week, El Salvador presented the commission with 17 charges that the Sandinistas supported Salvadoran leftist rebels.

Yesterday, Nicaraguan Undersecretary of Foreign Affairs Victor Hugo Tinoco disputed Duarte's claim. "No president is the referee or judge who will decide who complied and who did not," Tinoco said. "I can tell you what we have done, even though others have not complied. I am giving concrete examples -- the opening of La Prensa, Radio Catolica, the National Commission of Reconciliation . . . -- all despite the fact the United States continues to give money to the Contras."

{In Managua, The Associated Press reported, 10,000 Nicaraguans made a peaceful 10-mile march to protest against the Sandinista government and to mark the 10th anniversary of the death of La Prensa publisher Pedro Joaquin Chamorro.}