President Belisario Betancur, a leading opponent of military intervention in Central America, says the Reagan administration's request for $100 million in aid to anti-Sandinista Nicaraguan rebels is "wrong" and "will not produce good results."

In an interview, the Colombian leader, a founder of the Contadora group of eight Latin American states proposing a negotiated peace in Central America, said "all of Latin America doesn't like the Reagan proposal" and urged the U.S. president to talk with, not fight the Sandinistas in Nicaragua.

"I think that an initiative such as the request for $100 million taken by President Reagan is wrong," said Betancur. "I know we can get more through negotiation. I know that the Reagan administration is aware of the fact that Latin America has its own language, and that language is expressed through Contadora."

The extent of Latin American support for the aid request has been a point of controversy in Washington. Administration officials contend that some Latin American leaders do not want to endorse the plan publicly for domestic political reasons but that privately they are sympathetic with the U.S. anti-Sandinista campaign.

Betancur's firm opposition was expressed during a 45-minute interview Friday assessing his four-year term in office, which ends in August. Colombians went to the polls today to elect a new Congress in a vote that foreshadows presidential elections in May. The Colombian constitution prevents presidents from seeking a second consecutive term.

A man of peasant background and populist political skills, Betancur, 63, was elected on a platform of achieving peace at home with leftist guerrillas and abroad between warring groups in Central America. Although the peace agreements he sought are far from being realized fully, Betancur said he has established a legacy of negotiation on both fronts. He is constitutionally prohibited from running for a second consecutive term.

The silver-haired leader calmly rejected the claims of critics on both the right and the left who regard his peace policies as having disintegrated in the face of mounting guerrilla warfare in Colombia and heightened tensions between the United States and Nicaragua. He said he had established an "anti-Vietnam approach" to armed conflict in the region, an approach of "dialogue and agreement" that, he added, is now irreversible, at least in Colombia.

"It is also the philosophy of the Contadora group," he said. "It consists in telling the guerrilla groups in Central America: Why not talk, why not search for diplomatic solutions and negotiate?"

The Contadora process is stalled at the moment over the refusal of the Sandinistas to talk with the rebels known as contras -- short for counterrevolutionaries -- and U.S. refusal to resume conversations with the Nicaraguan government under existing circumstances.

Despite Betancur's emphasis on negotiated solutions, his own room to maneuver with guerrilla groups in Colombia was dramatically called into question last November, when security forces stormed Bogota's main courthouse, which had been seized by April 19 Movement (M19) guerrillas, killing not only the terrorists but also 11 of 24 Supreme Court members and more than 50 other hostages held inside.

A number of Colombians and foreign analysts suspect that military leaders, who were never comfortable with the peace process, moved against the guerrillas without consulting Betancur, leaving the president to assume responsibility for the massacre to uphold the image of civilian authority. Since then, the Army has increased operations against M19 and other smaller guerrilla groups concentrated in southern Colombia.

Defending the institutional integrity of his government, Betancur reiterated that he had been in full charge during the 27-hour siege at the Palace of Justice. He said military forces had been permitted to continue advancing on the building to prevent the guerrillas from consolidating their position inside.

He blamed the M19 attackers for the carnage, saying they had refused to drop their guns and accept his nonnegotiable offer of a fair civilian court trial if the hostages were released. He said he had been willing to "converse" with the guerrillas, "offer them a way out, a solution," but not "negotiate" with them after they had taken over the building, killing guards and others.

Asked why, several hours after the midday attack began, he had declined to take a frantic telephone call from a trapped Supreme Court president pleading for a cease-fire that might have permitted a dialogue, Betancur said he had passed the call to police Gen. Victor Alberto Delgado "because the operation taking place was a military operation, directed by the police chief."

The president was reluctant to discuss other details of the incident. He noted that a special judiciary commission was due to report this month on the siege.

Countering public perceptions that full-scale guerrilla warfare has resumed, Betancur said that a two-year-old cease-fire with the Revolutionary Armed Forces of Colombia, or FARC, the country's oldest and largest rebel movement, remains in effect. Government and FARC representatives signed an agreement a week ago extending the truce indefinitely, and FARC has set up a political front, the Patriotic Union, which is running candidates in this year's elections.

Betancur said dealing with Colombian guerrillas has been complicated by the contrasting nature of various groups. FARC, for instance, which Betancur said represents 90 percent of the insurgents, is linked to the Communist Party, while the M19 is a nationalist force with no clear international ideological connections.

Moreover, said Betancur, violence has been chronic in Colombia. "We are trying to solve a problem 40 years old," said the president. "That's not possible overnight. What I'm satisfied with is having brought the peace process to a point of no return."

Betancur said investment in poor regions where guerrillas recruit will be the government's best defense against subversion. He said legislation passed last year authorizing the election instead of appointment of mayors starting in 1988, and facilitating the formation of new parties, will widen participation in politics.