NEW YORK, OCT. 7 -- Nicaraguan President Daniel Ortega said that continued U.S. aid to the contras after the five-nation Central American peace agreement takes effect Nov. 7 would violate the accord and relieve his Marxist government from its obligation to observe the regional pact.

In a two-hour meeting with a group of reporters here Tuesday night, Ortega noted that the agreement bars outside assistance to insurgent forces in any of the five countries. But, he added, no matter what Congress does about President Reagan's plan to seek an additional $270 million in military aid for the contras, Nicaragua has "an overriding commitment to continue trying to implement the agreement" signed by him and the presidents of Costa Rica, El Salvador, Honduras and Guatemala at Esquipulas, Guatemala, last Aug. 7.

"It is simply a fact that if aid continues to flow to the contras, even if it is aid already in the pipeline, it would violate the agreement, which says specifically there should be a total cessation of outside aid," Ortega said. "If on Nov. 7, the president of the United States does not declare an end to all direct or indirect contra assistance, then we would be under no obligation because there would be none of the simultaneity that the United States says is crucial to effective implementation of a peace agreement," Ortega said.

"At that point, we'll have to confer with our neighbors and see how to confront the total disrespect of President Reagan for what the five Central American presidents have decided. After all, they are agreements made between five Central American governments. They are not agreements made in the United States."

Ortega, who was interviewed shortly after his arrival here Tuesday night, made his remarks before Reagan, in a speech Wednesday to the Organization of American States, reiterated that the Guatemala accord is insufficient to resolve U.S. concerns in the region and vowed to keep fighting for contra aid. Nicaraguan officials said they expect Ortega to make a detailed response when he addresses the U.N. General Assembly Thursday.

In the interview, Ortega stressed these themes in describing his government's position:He charged that the contras are not the cause of Nicaragua's problems but a symptom of the Reagan administration's determination to destroy the Sandinista revolution, and he reiterated his past calls for a "direct dialogue between Nicaragua and Washington to normalize relations." He said that U.S. concern about the agreement's failure to ban Cuban and Soviet military aid to Nicaragua should be discussed within the context of this U.S.-Nicaraguan dialogue and the peace agreement's provisions for negotiations to reduce armaments and remove all foreign military advisers from the region. He rejected U.S. demands for negotiations with the contras on a cease-fire as a "propaganda trick" to sabotage the peace process by having U.S.-controlled contra leaders "who live comfortably far from the battlefields make absurd demands." Instead, Ortega said, contras who actually have been fighting in the Nicaraguan backlands and who sincerely want to discuss a cease-fire and amnesty can do so through the national reconciliation commission headed by Cardinal Miguel Obando y Bravo. He said that although he and other Sandinista leaders are Marxists, they favor a course that guarantees political pluralism, a mixed economy and nonalignment for Nicaragua. Ortega said any Nicaraguans, including all contra leaders in exile, are free to return and challenge the Sandinistas in the presidential elections scheduled for 1990. If the electorate goes against him, Ortega insisted, the Sandinistas will surrender power and go into opposition.

But Ortega put his greatest emphasis on arguing that Reagan's rhetorical hostility toward the Sandinistas and his insistence that he will never desert the contras are a sign that he "does not intend to end his policy of war toward Nicaragua . . . . If over the next 30 days the contras come in massively to accept amnesty, is the problem over? {Reagan} still could turn to other ways of imposing his conditions. If there is peace and the president does not change his policy, we can only expect the worst, including direct military intervention."

That, Ortega said, is why he dismisses U.S. demands for cease-fire negotiations as a trick to force him into talks with what he described as U.S. puppets such as Adolfo Calero, a prominent member of the contra movement's political directorate, and Enrique Bermudez, the contras' military commander.

"Let's suppose there was a dialogue," he said. "The leadership of the contras would have a series of absurd demands. The dialogue would fail. Then President Reagan would come before Nov. 7 and say: 'The dialogue has failed. I want my $270 million.'

"The Bermudezes and the Caleros are waiting for the $270 million so they can line their pockets. They go from Miami to Costa Rica to Puerto Rico -- from hotel room to hotel room. It's very comfortable for them. It's a good business for them. But it's the contras on the ground who are suffering, and we make a clear distinction between them and those others."

He said those who are fighting inside Nicaragua are the object of his plan for neutral cease-fire zones where contra forces can gather without fear of attack and talk with representatives of the reconciliation commission about the conditions for amnesty. The plan goes into effect this week, and Ortega said that, largely because of appeals from families still in Nicaragua to end the bloodshed, he expects a "very substantial number" of contras to accept amnesty.

About those who refuse, Ortega said: "If on Nov. 7, there are contras who are not talking about a cease-fire and not accepting the amnesty, well, they are going to find themselves facing the full weight and pressure of our armed forces."