President Felix Houphouet-Boigny of the Ivory Coast predicted yesterday that Libya's Col. Muammar Qaddafi can now be blocked in his efforts to overthrow African and Arab governments if the United States and other big powers will support the Organization of African Unity's repudiation of Qaddafi with their own actions.

"We have done what we can" by rejecting Qaddafi's bid to become the OAU's president, said the Ivorian leader, who is sub-Saharan Africa's senior statesman and a leading advocate of cooperation with the West. "But Qaddafi supports radical nations and movements across the world, and it is up to the big powers to act with the means at their disposal."

In an hour-long interview, the 77-year-old, French-speaking African leader also offered an endorsement of the Reagan administration's efforts to negotiate a peaceful settlement to the guerrilla war being fought in Namibia between South African forces and African insurgents. The only alternative to these peace efforts, he warned, would be a widened war that would result in the occupation of African nations by the white minority that rules South Africa.

"If that happens, African countries then will be coming to the United Nations to ask for the evacuation of their occupied territories," rather than asking for the independence of Namibia, Houphouet-Boigny predicted. "And the result will be tens or hundreds of condemnations by the U.N., and nothing else."

Houphouet-Boigny met with President Reagan Tuesday and said that he had been impressed by a new American determination "to make its presence felt in Africa and elsewhere again." The Ivorian has met with every U.S. president except Jimmy Carter since Dwight D. Eisenhower, whom he met while serving in the Cabinet of Gen. Charles de Gaulle of France in 1958. The Ivory Coast became independent of France in 1960, and Houphouet-Boigny has presided over the coffee- and cocoa-producing nation since in a paternalistically authoritarian manner.

He cited his own travels to Washington as an example of how he thinks southern Africa's continuing racial problems have to be solved. "I never thought when I first started coming here that one day I would be welcomed, as I was this time, by a black mayor of Washington. That change came from inside, because Americans decided they had to change. No one came from outside to make them do it."

Fear and selfishness, he said, "are the dominant forces in the world today, and the 4 million whites in South Africa are fearful of the demands of equality from our 20 million African brothers. They are afraid they will have to share what they have. They must make an effort, and we must continue to try to have a dialogue with them. And the United States must persist in its efforts, since there can be no solution without the United States."

South Africa's neighbors "have to avoid what the Arabs could not avoid with Israel. Tunisian President Habib Bourguiba recommended a dialogue with Israel" in 1965 "but his Arab brothers did not listen to him, and the result was the occupation in 1967 of Arab lands by Israel. Given South Africa's military power, we run the risk of the same scenario being repeated with its neighbors," Houphouet-Boigny said.

He was openly buoyed by the decision Wednesday of the OAU to pass over Qaddafi and to elect Ethiopia's Mengistu Haile Mariam as this year's chairman.

The conference in Addis Ababa also blocked Qaddafi's efforts to have the Polisario Front, a guerrilla movement that claims to represent the disputed territory of the Western Sahara, seated as the OAU's 51st member.

Houphouet-Boigny indicated that Qaddafi had overplayed his hand in forcing the Polisario issue. "He was rejected first as a matter of principle, since the OAU does not accept organizations like Polisario as member states. I have been involved in the OAU for 20 years, and we have never accepted fighters as members, whether it was the Algerians during their struggle for independence or the organizations of Zimbabwe."

Secondly, he noted, Qaddafi still has Libyan troops stationed in northern Chad.

"How can you be the president of an organization when you are occupying part of the territory of a member state of that organization?" he asked. "That's difficult. We could not accept that."

Africa, he said, "has done its part." Houphouet-Boigny said that he had recalled to President Reagan in their meeting Reagan's declarations vowing to stop Qaddafi's international campaigns, and suggested that the United States and Europe must exert diplomatic and financial pressures on Libya, rather than undertaking military or covert efforts against Qaddafi.

The Ivorian also called for closer cooperation on economic matters between the United States and Africa. At international meetings, "the West talks to us like a doctor talks to a very sick person lying on a sick bed, saying how much better things are going. When you are too weak to get out of the bed, the words don't help much."

Special correspondent Mary Anne Fitzgerald reported from Addis Ababa that Qaddafi had boycotted the OAU's opening session Wednesday night, and African sources said that the boycott had caused him to lose face in the eyes of many of the leaders gathered at the conference.

Qaddafi's defeat demonstrated a diminishing ability to influence African politics and made his participation in next year's summit, in Conakry, Guinea, doubtful, Fitzgerald reported. Guinea's President Ahmed Sekou Toure helped gather support in Addis Ababa for Morocco's strong opposition to seating the Polisario.