Nicaraguan President Daniel Ortega, asserting that his Marxist Sandinista government is "ready to comply 100 percent" with the Central America peace agreement, charged yesterday that President Reagan has reneged on earlier promises of a "direct dialogue" with Nicaragua.

Ortega, speaking to the annual assembly of the 31-nation Organization of American States, objected to the terms specified by Reagan on Monday for high-level U.S. talks with Nicaragua. Reagan told the OAS that if the Sandinistas negotiate indirectly with U.S.-backed contra rebels, the United States would talk with Nicaragua in "a regional context" that must include the other four countries involved in the peace agreement.

Ortega, noting that he has asked Nicaraguan Cardinal Miguel Obando y Bravo to act as intermediary in discussing a cease-fire with the contras, said his government was keeping its part of the arrangement. He added:

"President Reagan had stated that when this type of contact was made and this type of initiative taken, the United States government simultaneously was going to begin a bilateral dialogue with Nicaragua . . . . We are waiting for President Reagan to fulfill his word because what President Reagan said a few days ago does not dovetail with what was said earlier.

"We are waiting for President Reagan to keep his word and begin a direct dialogue, government to government, between Nicaragua and the United States so that we may find a way to normalize our relations . . . . Since the United States says that we are a threat, we are ready to talk about this topic and arrive at firm, verifiable agreements. That is what we hope for; that is what we yearn for; that is what we aspire to."

U.S. officials acknowledged that the administration has said several times that it would resume high-level contacts with Managua if the Sandinistas agreed to deal with the contras. But, the officials added, the administration never specified the context or format of such talks, and one described Ortega's assertion that it was supposed to be a purely bilateral dialogue as "a very free translation of what we offered to do."

Richard T. McCormack, U.S. ambassador to the OAS, noted that Reagan had been very specific in stating that any talks must include the other four countries -- El Salvador, Costa Rica, Honduras and Guatemala -- that signed the peace accord in Guatemala last Aug. 7. McCormack added: "This government is prepared to go the last mile to reach accommodations that will help bring peace to Central America. But first we want to see concrete actions by the Sandinistas."

Other U.S. officials, who asked not to be identified, said the administration opposes bilateral talks because, they charge, the Sandinistas used a 1984 round of negotiations as a pretext for impeding progress in other multination efforts to resolve Central American tensions.

The sources also said that Honduras and El Salvador, close U.S. allies, do not like the idea of exclusive talks between Washington and Managua because they fear Washington would make agreements covering U.S. concerns about Nicaragua's military and political ties to Cuba and the Soviet Union, but might not address Central American desires to limit the size of the Nicaraguan armed forces and halt Nicaraguan interference in their affairs.

Ortega, in a gray business suit rather than the military uniform he customarily wears on public occasions, delivered a long, rambling address that many delegates privately described as lacking dramatic impact. He spent about half his time restating lengthy legal arguments about whether the Sandinistas had broken a 1979 pledge to the OAS to move rapidly toward democratization of Nicaragua after the overthrow of the late dictator Anastasio Somoza.

He also spent considerable time reading excerpts from the finding last year by the International Court of Justice in The Hague calling for the United States to end contra aid. The administration, aware that past Central Intelligence Agency activities such as the mining of Nicaraguan harbors would strengthen Nicaragua's legal case, had refused to accept the court's jurisdiction over U.S. disputes with Nicaragua.

Ortega also repeated charges that the United States has continued a "terrorist war against Nicaragua" despite the Aug. 7 agreement by continuing to supply weapons to "mercenaries who get their salaries from the CIA" and sending reconnaissance flights over Nicaraguan territory.

He said that an international commission of the OAS and United Nations, which is scheduled to report in January on how the agreement has been implemented, is "welcome to visit any part of the territory of Nicaragua. Wherever the commission says it wants to go, you may be sure that it will go there . . . . The mercenary forces do not control one inch of our country."

Ortega met later yesterday with House Speaker Jim Wright (D-Tex.), a strong supporter of the Guatemala agreement. Emerging after a 90-minute session with Wright, Ortega said "this would be a good time" for Reagan to meet with him. While flying here Tuesday, Ortega told a New York Times reporter on his plane that if Reagan were willing to receive him, he would consent to contra leaders being present at the meeting.

However, administration officials have said that since the indirect talks with the contras have not started, there is no chance of Ortega meeting with Reagan or Secretary of State George P. Shultz. Obando is expected to come here tonight, but contra leaders said yesterday that his mission involves talks with U.S. bishops and that he will not function as an intermediary while here. Instead, they said, the tentative plan is for the first contacts to take place next week in either Costa Rica or Guatemala.