SAN JOSE, COSTA RICA, FEB. 6 -- Costa Rican President Oscar Arias Sanchez today called on the Soviet Union and Cuba to cut all military aid to Marxist rebels in Central America as the next step in the regional peace process.

Arias welcomed Wednesday's vote by the House of Representatives rejecting further military aid to U.S.-backed Nicaraguan rebels known as contras. He said the vote should not be "interpreted in favor of {Nicaraguan President Daniel} Ortega, but as an opportunity for the peace plan" signed by five Central American presidents last August to end armed conflict and encourage democracy in the region.

In an interview at his residence, Arias said, "Now that aid has been cut to the contras, we must also ask the Soviets as well as the Cubans and all those who have been supporting the guerrillas in El Salvador and Guatemala to cut that aid."

He added that Soviet military aid to Nicaragua's Sandinista government should also be eliminated because "disarmament is part of our plan."

Arias said he has not yet approached the Soviet Union or Cuba to secure their cooperation with the peace agreement in halting military aid to the Marxist-led insurgencies in the region. But he indicated that he plans to do so.

Arias said he hoped peace in Central America will be high on the agenda when President Reagan meets Soviet leader Mikhail Gorbachev at the next summit in Moscow later this year.

He also called on U.S. Secretary of State George P. Shultz to open direct talks with the Sandinistas.

"We should never be afraid of talking to our adversaries," Arias said.

The Costa Rican leader, who was awarded the 1987 Nobel Peace Prize for conceiving the regional peace plan, criticized what he viewed as Ortega's hard-line response to the defeat of contra aid.

"I think his response to the vote should have been much more conciliatory and not, as it was, announcing that the war was going to continue," Arias said.

He declared that Ortega now has "no more excuses" for not complying fully with the requirements of the peace accord, including cease-fires, general amnesty and democratic reforms.

Arias said one key reform by Nicaragua should be the abolition of the ruling Sandinista party's control over the armed forces, as demanded by its civilian political opponents.

If the Sandinista government does not meet the terms stipulated by the peace agreement, Arias said he would seek to apply "moral, diplomatic, economic and political pressure" on Managua to put democratic reforms into effect.

"Ortega is the first communist leader since 1917 who committed himself to democratizing his country," Arias said. "If he does not honor his word, he will be isolated from everybody who gave him support in the past."

Arias refused to specify how world pressure on the Sandinistas could be applied, but observed that the termination of U.S. military aid to the contras is "reversible."

"If they {the Sandinistas} do not advance toward full compliance with the accord, the Democrats could even be tougher than the Republicans because they are the ones trusting the Sandinistas more than everyone else," Arias said.

Asked about a House Democratic plan to introduce legislation for nonlethal aid to the contras, Arias said this "would not be a violation of the peace accord. It is military aid that is prohibited and not humanitarian aid."

In contrast to the Reagan administration, Arias has consistently argued that military pressure from the contras would not bring about a democratic government in Nicaragua.

Rather, he said that Ortega has "used the aggression of the contras as an excuse for the failure of the Marxist experiment in Nicaragua" and for a lack of progress toward democracy.

Arias said he believed that Ortega accepted the peace plan's terms for establishing democracy with great reluctance, reflecting the suspicions of more truculent Marxists among the Sandinistas' nine-man ruling directorate.

"The hard-liners in Managua certainly prefer to fight in the military field and not in the democratic field," Arias said.

"I think the Achilles heel for a despotic government, mainly if it is a Marxist government, is democratization and not military pressure. That is why I have used the metaphor that the only way to kill Dracula is with a crucifix."

The Costa Rican leader said he is optimistic that the Sandinistas will move more quickly toward a cease-fire with the contras when representatives of the two sides meet Wednesday in Guatemala for a second round of direct talks aimed at reconciling major differences over the terms of a truce.

"Without new military aid being approved for the contras, I really do hope that progress in these talks will come much faster," Arias said.

If a cease-fire between the Managua government and the U.S.-supported rebels is reached, Arias said, Nicaraguans who have taken refuge in Honduras from the Sandinistas "will have to choose between staying in Honduras forever and abandoning military activity or returning to Nicaragua under an amnesty that should be provided and gradually incorporating themselves into political life."

He said that "exactly the same thing should happen in El Salvador" in the case of Marxist-led rebels who have been waging a guerrilla war against the Salvadoran government for more than eight years.

Arias said that Nicaragua's actions in response to the peace pact have received greater scrutiny so far because "other countries have complied much more with the terms of the Guatemala accord."

He said now that the "sword of Damocles" has been removed by the vote against further military aid to the contras, Ortega knows that "the future of peace in Central America lies in his hands."