MANAGUA, NICARAGUA, NOV. 18 -- President Daniel Ortega, after eliciting from an editor of the opposition daily La Prensa that it opposed the Reagan administration's proposed aid to the Nicaraguan rebels, said today that the newspaper will not be closed again if it maintains that position.

Ortega's assurances for La Prensa, which was shut by the leftist government in June 1986 for 15 months, came after he engaged the paper's current news director, Cristiana Chamorro, in a debate during a televised roundtable dicussion with Nicaraguan journalists.

The discussion, and Ortega's unusual face-to-face debate with Chamorro, were part of his efforts to be open to political dialogue in the final weeks before the five Central American presidents will determine the compliance with a regional peace plan initiated Nov. 5.

After fielding many questions, Ortega suddenly demanded that Chamorro answer his question: Does La Prensa support the Reagan administration's request for $270 million new aid for the rebels? While insisting that Ortega should allow greater democratic freedoms in Nicaragua, Chamorro finally said her newspaper does not support the aid.

Surprised, Ortega said, "If that is La Prensa's position, then you will not be affected by any restrictive measures we might take if the U.S. Congress approves the $270 million. Only those who are tools of the CIA will have to worry. Those who are free from sin need not fear."

Earlier, Ortega had promised the government would impose a "full state of war" in Nicaragua if Congress approved more military aid for the rebels, including a new shutdown of La Prensa and broad restrictions on all media.

"When the United States pursues a policy of force with Nicaragua, it results in a closing of the political space in this country," Ortega said.

Meanwhile, Ortega also offered assurances to Cardinal Miguel Obando y Bravo, who was asked by the government to serve as an intermediary in indirect cease-fire talks with the contras.

"The intermediary is not just a mailman. He must have an active role, giving suggestions, opinions, advice," Ortega said. The cardinal has demanded a letter to guarantee he will have a substantive role. Ortega gave no word of the letter today.

But the president again rejected one of the cardinal's requests, that the dialogue take place in Nicaragua. Ortega warned that the Sandinista National Liberation Front would mobilize to confront any contra leader who returned to Nicaragua for talks without accepting a government amnesty.

Chamorro asked Ortega if he would accept the result of new elections if they were held before the end of his term in 1989 and he were defeated. Ortega responded that his party probably would take more than 80 percent of any national vote today. "We think we should give the opposition a little time to get organized," the president said.