The summit meeting of the Organization of African Unity collapsed today for the second time in four months, opening the way to formation of rival ideological blocs among the 50 member nations.

After three days of almost nonstop informal talks to resolve the issue of representation for the embattled central African nation of Chad, African leaders gave up and began flying home. In August, they also had come to Tripoli and failed to convene their annual summit.

A veteran African foreign minister, who declined to be identified, said before the summit failed again: "The OAU is finished. It's better to let the patient die than have him continue with such a sickness."

Other, calmer voices said the OAU could well try for a third time to hold a summit, but next time possibly at the organization's headquarters in Addis Ababa, Ethiopia, where Libya's opposition to Chad's pro-Western leader Hissene Habre would not be an issue.

OAU spokesman Peter Onu told a press conference that the heads of state had appointed a 12-nation contact group to make another attempt to have a summit. No provision was made by the leaders about where the summit should be held, he said.

Libyan leader Col. Muammar Qaddafi, however, told the informal session of 30 leaders that "it is impossible to meet again." Wearing an Army trenchcoat and waving his fist frequently, the virulently anti-American leader blamed the United States and France for the failure of the summit. He made similar charges against the United States after the August failure of the summit but never gave specifics.

Tonight, he congratulated some of the leaders for coming to the conference "despite pressure put on them by Washington and orders from Paris" which, he said, were applied throughout Africa.

A collapse of the OAU--the world's largest regional organization with 50 members -- could have a major impact on Africa's drive to end the continent's last examples of white-minority rule, in South Africa and Namibia.

If the organization did not revive, it could split into rival camps, pro-Western and pro-Soviet, leading to greater potential for Africa to become a theater of East-West conflict.

Although representational disputes over the former Spanish colony of Western Sahara in August and this time over Chad were the immediate issues that prevented the scheduled summit meetings, it appeared that opposition to Qaddafi triggered the two failures.

A group of mainly conservative West African countries blocked achievement of a two-thirds quorum of the membership and thus stymied the summits. Many of them are implacable foes of Qaddafi, who has been accused of fomenting dissidence and terrorism in a number of African countries.

Several delegates said there would be no trouble staging the summit anywhere but in Libya. Had it met here, Qaddafi would perforce have become chairman of the OAU, and Africa's unofficial spokesman, for a year.

The latest blow to the summit was delivered this morning when the Chadian government of Habre, whose military forces ousted a regime supported by Qaddafi earlier this year, "categorically rejected" an OAU compromise on representation offered last night. The proposal was to recognize Habre's government, but ask it to absent itself from the conference in deference to the Libyan hosts.

Kenyan President Daniel arap Moi, chairman of the OAU, held meetings over the last three days with African leaders, including Qaddafi, in search of a compromise to allow the summit at which he would turn over the chairmanship to the mercurial Qaddafi.

"There's no way Qaddafi can admit Hissene Habre," a Kenyan official explained. It would be hara-kiri to have Habre or his delegation in Tripoli, the official said, because many Libyan troops were killed by his guerrillas before Qaddafi pulled his forces out of Chad a year ago.

On the other hand, the official added, "there's no way we can get a quorum" without Habre's delegation being seated. Only 30 countries attended the abortive summit, four short of a quorum. Egypt, Sudan and Somalia refused to attend because of opposition to Qaddafi. Another 15 nations boycotted to demand the seating of Habre, and that was enough to block the summit again.

The summit originally scheduled for August collapsed because of a similar boycott over the admission of Western Sahara as a member. Morocco, which claims Western Sahara and is fighting the Libyan-backed Polisario Front guerrillas for control of the area, led that boycott.