SAN JOSE, COSTA RICA, AUG. 25 -- President Oscar Arias says he hopes the Reagan administration will wait to ask Congress for new aid to the Nicaraguan rebels until after Nov. 7, the date when a peace plan signed by the five Central American presidents is scheduled to take effect.

In an interview yesterday, Arias said he doubts the leftist Sandinista government of Nicaragua will comply with the plan, but hopes that all the nations involved, including the United States, will focus their efforts in coming months on meeting its conditions.

"I would prefer for the Reagan administration to wait until after Nov. 7 to knock on Congress' door for more aid for the contras," Arias said, referring to the Nicaraguan rebels. "I can't and shouldn't address myself to President Reagan with a concrete request. But the events are in the hands of the Central Americans now. We should have a chance, we deserve that chance until Nov. 7."

Arias, who is considered the principal author of the Central American peace plan approved Aug. 7 in Guatemala City, made a whirlwind tour through the region shortly before the summit to secure support of all five heads of state.

In Managua, President Daniel Ortega said three Roman Catholic priests exiled more than a year ago will be allowed to return. Meanwhile, three directors of the Nicaraguan resistance said they are prepared to return to Nicaragua if their safety could be guaranteed under an amnesty provided by the Arias plan. {Story on Page 19.}

The 11-point plan calls for an end to foreign aid to guerrilla groups in the region, a return to democracy in each country, and a region-wide cease-fire, among other points. All measures are to take effect simultaneously Nov. 7, that is, 90 days after the signing.

Nicaragua agreed to make sweeping changes to observe civil liberties that the Sandinistas have curtailed until now.

Administration officials have criticized the pact, saying it could disarm an estimated 10,000 Nicaraguan rebels, known as contras, and end their U.S. support, while leaving the Sandinista government in power without restricting the Soviet Bloc aid it receives.

Administration officials gave assurances 10 days ago, however, that no request for new aid to the contras will be sent to Congress before Sept. 30. In a message beamed into Nicaragua last night on the contras' Radio Liberacion, Reagan said he would "remain firm" in his aid policy and told contra fighters "we must not stop" until they can "return to a free Nicaragua."

The current $100 million assistance runs out Sept. 30 with the end of the fiscal year, but contra field commanders have said they have enough equipment to fight until December.

Deputy Assistant Secretary of State William G. Walker, on a trip through the region, met here Monday with Foreign Minister Rodrigo Madrigal Nieto to express U.S. concerns about "gaps" in the accord, the minister said.

But Arias rejected suggestions that the plan lacks detail.

"Nothing men do is perfect, only God makes perfection. I presented a viable peace plan, not an encyclopedia on the topic of peace," he responded.

Many diplomatic observers, describing the plan as too broad to succeed, say its main goal may be to expose what Costa Rica sees as the repressive nature of Sandinista rule.

Arias acknowledged Costa Ricans are skeptical that the Sandinistas will come through. "The great majority of Costa Ricans think the Sandinistas won't do it," he said. "I count myself among that majority. But my job is to do everything I can to see they do."

The president of Costa Rica, the only longstanding democracy in the region, insisted that the intent of the plan is to put an end to guerrilla wars such as that the contras are waging. "If everything -- democracy and cease-fire -- goes into effect at once, then the idea is to to abandon the armed struggle as a way of attaining power," he explained.

Arias said that a peace plan offered in the days before the Guatemala summit by Reagan was a catalyst that helped the presidents reach an agreement, but that it was superseded by the final pact. Reagan's plan required Nicaragua to halt its arms buildup and stop accepting Soviet Bloc aid. U.S. officials indicated the contras would have a role in negotiating the cease-fire foreseen by that plan.

In the Central American plan, Arias said, four-member oversight commissions to be named in each country will have sufficient authority to detect and denounce, even in Nicaragua, any violations of the accord.

Last Friday, the six leaders of the Nicaraguan Resistance, the contra alliance, emerged from a meeting in El Salvador with President Jose Napoleon Duarte to accept the plan and call for direct talks with the Sandinista government in Managua Sept. 15. Nicaraguan Foreign Minister Miguel d'Escoto retorted that his government would talk with what he called the contras' "top leadership," meaning Reagan, but would not meet with the contras.

Arias noted that the pact does not require direct talks between governments and rebel armies like the contras. They can be represented "perfectly adequately" by Cardinal Miguel Obando y Bravo, Nicaragua's Roman Catholic leader, or by other members of the commission, the Costa Rican said.

As a result of the pact, Duarte has moved to reopen with guerrillas fighting in El Salvador the talks that collapsed in late 1984. "That is a different case," Arias said. "The Salvadoran government was willing long before my proposal to talk with the guerrillas. There's no reason why it shouldn't continue that now."

Arias, 46, is confidently basking in the limelight that has fallen on him since since the Central American summit, which even brought a nomination for him to be awarded the Nobel Peace Prize. He said the political gain for his sometimes overlooked country will not be erased even if the effort fails: "Costa Rica already won. The world knows now that we are an oasis of tranquility. No one can mix us up with Puerto Rico anymore."