MANAGUA, NICARAGUA, NOV. 5 -- President Daniel Ortega, marking the first deadline of a regional peace plan, announced tonight that the government will seek a nationwide cease-fire with leaders of U.S.-backed rebels in indirect talks through an intermediary.

The leaders of the Nicaraguan Resistance, the broad alliance of the rebels, known as contras, immediately accepted Ortega's proposal and claimed it as a political victory for their cause. It was the first time the Sandinista government has accepted any form of dialogue with the contras in the five-year-old conflict.

Ortega also pardoned 981 political prisoners and said the leftist government will lift a state of emergency nationwide and enact a sweeping amnesty as soon as an international monitoring commission verifies that U.S. and Honduran aid to the contras has ceased, as the peace agreement requires.

Ortega's cease-fire announcement represents a sharp shift by the Sandinista government, which as recently as yesterday reiterated its refusal to hold any dialogue with top contras. The decision breaks a major logjam in the unprecedented regional peace process, begun 90 days ago with the signing in Guatemala of the accord by the five Central American presidents.

{In Costa Rica, the main author of the plan, President and 1987 Nobel Laureate Oscar Arias, described Ortega's announcement as "a positive step," Knight-Ridder reported.} Arias had earlier said a negotiated cease-fire in Nicaragua was the main sticking point in the complex regional process.

"The impasse must be broken," Arias warned. "If we can do that {achieve a bilateral cease-fire} we will be able to force Honduras to get rid of the contras, and we can prevent more supplies from reaching the contras."

Arias called on the Sandinista government to accept Cardinal Miguel Obando y Bravo, the head of a four-man National Reconciliation Commission that monitors the accord, as a mediator for indirect talks.

Top Sandinista officials gave no indication tonight of whom they will pick as a go-between or what procedure they will follow. Contra leader Pedro Joaquin Chamorro said by telephone in San Jose, Costa Rica, that the cardinal is the only mediator the Nicaraguan Resistance will accept.

According to news reports from the Honduran capital, Tegucigalpa, President Jose Azcona made no public statement or appearance today and there were no other festivities to mark the deadline.

Nicaragua has accused Honduras of dragging its feet in expelling contra military operations from its territory. Both nations have said they will not move faster until the other has complied fully.

Ortega said the government initiated the indirect dialogue "to take all the excuses away from our enemies, who say we don't want peace when they are the ones who don't want peace" -- a reference to the Reagan administration. The Sandinista government has been under intense pressure from Arias, the other Central American governments and Washington to accede to an indirect dialogue.

The president stressed that the communication with contra leaders would not involve "a political dialogue to negotiate for power." The issue is sensitive for the Sandinistas, because it forces them to recognize the legitimacy of the 9,000-fighter contra army, which they have dismissed as U.S.-paid mercenaries.

Ortega delivered his hour-long speech before a boisterous, festive crowd of about 30,000 gathered in downtown Managua to celebrate the accord. His speech was punctuated by choruses of such Sandinista slogans as "Over here, over there, the yankee will die."

Many Sandinista followers carried posters saying, "No political dialogue with the top mercenaries." Last week the ruling Sandinista National Liberation Front, in a fiery statement, said there would "never" be a political negotiation with contra leaders.

The crowd tonight lapsed into an uneasy silence when Ortega made his announcement about the cease-fire talks.

Contra leaders said they will accept an agenda that deals only with cease-fire matters. "We have never asked for talks about anything having to do with power," said another Nicaraguan Resistance director, Alfredo Cesar, from San Jose.

But the contras predicted that the indirect communication would in time turn into face-to-face talks with the Sandinista government.

Today's pardons take effect immediately. The list includes the majority of 618 political prisoners designated for pardon last March by the National Assembly, according to Gustavo Parajon, a member of the National Reconciliation Commission. Ortega never signed that pardon into law.

Ortega today sent to the Sandinista-controlled National Assembly two bills to end the five-year-old state of emergency and legislate a broad amnesty for political prisoners. The bills would take effect when the international verification commission established under the peace pact determines that the contras are not receiving any aid from Honduras or the United States.

The verification commission, made up of 13 Latin nations, the United Nations and the Organization of American States, is to meet Saturday in Washington to plan a series of on-site inspections to monitor compliance. It is scheduled to make its first report Dec. 7.

Meanwhile, Ortega said that three small cease-fire zones that were set up Oct. 7 will be dismantled Saturday and fighting will resume there. Ortega said that about 600 Nicaraguan contras had accepted an amnesty to lay down their arms in the zones, but he complained of violations by the contras.

"After Nov. 7 we're going after the contras who don't want to accept the amnesty," the president said.

Tonight's rally was attended by New York Mayor Edward Koch, here on a four-day visit to monitor the progress of the accords. Ortega said Koch is "not an enemy of the people," as the Sandinista anthem describes some Americans, and told him he was safer wandering amid the sea of Sandinista militants than he would be in the streets of New York.