Libyan leader Col. Muammar Qaddafi appeared to be virtually isolated in much of Africa after two abortive attempts -- that cost his government more than $50 million -- to hold a summit meeting of the Organization of African Unity.

At last night's failure to convene the annual summit, Qaddafi blamed the United States and France for the second collapse of the conference in four months.

Delegates from a few radical countries privately agreed. Many others acknowledged American opposition to the Tripoli summit but denied the United States sabotaged it and said the meeting could have taken place anywhere but in Libya.

Only Ethiopia, Mozambique and Madagascar, all ruled by leftist governments, publicly backed the Libyan leader in opposing recognition of the pro-Western Chadian government of Hissene Habre, which was the immediate reason the OAU could not attain a quorum of 34 of the organization's 50 member nations.

As African leaders left Tripoli today for the second time since August without being able to hold their conference, it was clear that they would not return for a third try.

Tripoli was like the morning after a party that never got off the ground. The flags, banner and lights were still up. The scores of Chevrolet limousines and BMW police motorcycle escorts were still parked in front of the Grand Hotel housing the leaders, but the drivers had little prospect of work except for one last trip to the airport.

Even before last night's failure, many delegates had grumbled that the deadlock over Chad was simply a Libyan problem. Some pointed out that Habre's government had had no problem in assuming Chad's seat at the United Nations.

Some southern African delegates complained that Africa's drive to end white rule in that part of the continent was being stalled by an issue that should not concern the OAU--the question of which faction represents Chad.

Habre's forces swept past an OAU peace-keeping contingent in Chad earlier this year to capture the capital, Ndjamena, and most of the rest of the country from forces of Goukouni Oueddei, who was supported by Libya.

"Judging how some other African governments gained power," one pro-Western foreign minister said, "it is amazing we would turn down a government that gained power by conquest rather than through a coup."

The August summit failed because of a division within the organization over representation for Western Sahara, where Libyan-backed Polisario Front guerrillas are fighting Morocco for the sparsely populated former Spanish colony.

On that occasion, the conference was almost evenly divided. This time, however, few countries supported Qaddafi, because there is little question that Habre controls most of Chad, one of the world's poorest countries.

Qaddafi took a number of contradictory actions regarding the OAU in the past few months that kept diplomats guessing about his intentions, but in retrospect they seem to have doomed the summit to failure.

"We've long since given up trying to put ourselves in Qaddafi's mind," one resident diplomat said.

When moderates supporting Morocco blocked the summit in August over the Western Sahara issue, Qaddafi softened his position, and Polisario agreed last month to absent itself from the summit.

At the same time, however, Qaddafi was taking other actions that led to the Chad crisis. Goukouni announced the establishment of a "national salvation government" in Bardai in northern Chad four weeks ago and immediately gained Libya's recognition. He operates mainly from Libyan soil.

In his closing speech last night, Qaddafi hinted that he may once again intervene in Chad as his troops did in 1980 to maintain Goukouni in power. They withdrew last year under OAU pressure as the Libyan leader sought to improve his image before hosting the summit.

"We have to support the Goukouni government since he has no guns," Qaddafi told the other 29 leaders at the meeting.

Diplomats report that Libya has rounded up between 10,000 and 15,000 Chadian refugees in the country and sent them to military camps in Libya or across the border in the area controlled by Goukouni.

It remains to be seen whether Qaddafi will once more intervene with his Army, equipped with several billion dollars' worth of arms supplied by the Soviet Union and other countries.

His troops suffered serious losses against Habre's forces--a key reason why Qaddafi could not stomach the idea of the Chadian leader's setting foot on Libyan soil. Habre's foreign minister, Idriss Miskine, led a delegation to the foreign ministers' conference here last week but withdrew, reportedly after being insulted by senior Libyan diplomats.

Qaddafi angered many French-speaking West African nations, which subsequently boycotted the summit, when he told the ministerial conference that their participation in a French-African conference in Kinshasa, Zaire, was "a disgrace" since they had previously refused to attend the OAU. He demanded an end to the annual conference between France and its former African colonies.

Earlier he had convoked their ambassadors and told them there was no reason for him to send ambassadors to their countries as he could simply send one to Paris to deal with them all.

He also embarrassed African nations with close ties to Washington in his address to the ministers by sharply attacking U.S. policy and saying Americans treated their dogs better than blacks. He added that "America feeds on the blood of the peoples of the world."

Some African delegates expressed bitterness that Qaddafi was putting Libyan interest in Chad ahead of continental unity. Libya claims an area of northern Chad known as the Aouzou Strip, which is believed to be rich in minerals. No detailed surveys have been done because the country, three times the size of California with only 4.5 million population, has been embroiled in almost two decades of tribal and civil wars.

Last week a Libyan official told reporters and diplomats that Chad was more important to Qaddafi than the chairmanship of the OAU. He further alienated other African leaders with his speech to the foreign ministers' conference, in which he belittled the role of previous OAU chairmen and said he was "not keen or enthusiastic" about assuming the post.

Nevertheless, Qaddafi seemed to covet the position. He had already reserved a time on Dec. 5 to address the United Nations General Assembly in the role of unofficial leader of Africa, a position that goes with the OAU chairmanship.

[A U.N. spokesman in New York said Friday Libya had informed the secretary general's office that Qaddafi's visit and address had been postponed "for the time being." No explanation was given, the spokesman said.]