TRIPOLI, Libya — Akram al-Warfalli, a leader of this country's giant Warfalla tribe, said only a few words in his interview with Al-Jazeera.

"We tell the brother Gadhafi, well, he is no longer a brother," al-Warfalli said, "We tell him to leave the country."

It was one defection from a powerful tribe that has supported Moammar Gadhafi — one small ray of hope for the rebels being pummeled by his troops in the east. Some Libyans and scholars outside the country say the system of tribal alliances that has long been Gadhafi's most potent weapon is emerging as perhaps his greatest — and only remaining — vulnerability, as a long history of external wars, failed tribal coups and internal purges have chipped away at his support even among the tribes.

Gadhafi's reaction to the tribe's mutiny was swift, another Warfalla leader recalled Monday, dispatching fighting units to the Warfalla's traditional homeland, Bani Walid. There they made sure no younger tribe members left to join uprisings in the nearby cities of Zawiyah and Misuratah as well as the capital, this Warfalla leader said, speaking on the condition of anonymity for fear of retribution against himself and his family.

"The Warfalla, like their brethren the Zintan and Awlad Suleiman, are boiling," he wrote in an e-mail, referring to two neighboring tribes. "The only reason we have not seen them participate in combat is the lack of weapons, and the siege that is now implemented upon them. They are simply outgunned, and are vulnerable."

A Gadhafi government spokesman, Abdel Majid al-Dursi, disputed the Warfalla leader's account, saying the tribe's support for Gadhafi remained strong. From the moment he seized power in 1969, Gadhafi has surrounded himself with a bulwark of close allies drawn from his family, his own tribe, the Qaddafa, and two larger central and western Libyan tribes with close ties to his own, the Warfalla and the Margharha. All three tribes — the Qaddafa most of all — have dominated the ranks of Gadhafi militias and armed forces, jobs that carry significant power, prestige and money in Libyan society and culture, They remain his sturdiest base of support.

But as Gadhafi has maneuvered through four decades of treacherous tribal politics, he has made many enemies, and even his own tribe and its allies have increasingly turned against him. The tensions flared into the open as early as 1985, when his guards shot and killed his cousin Hassan Ishkal, a top military commander, at the gates of Gadhafi's compound here; Ishkal had questioned the wisdom of the Libyan leader's losing war with neighboring Chad.

Intra-tribal stresses reached their most visible peak in 1993 when military officers from the three favored tribes, the Qaddafa, Warfalla and Margharha, staged an abortive coup. Now, since the recent revolt began, another Qaddafa cousin in the colonel's inner circle, Ahmad Gaddaf al Dam, has reportedly fled to Cairo.

As the tide of battle has turned recently thanks to Gadhafi's well-equipped militia, some rebels say they are pinning their hopes on a tribal coup organized by those still close to him.

"We pray for that every day," said Mohammed, a rebel in the besieged city of Misuratah whose family name was withheld for their protection. "There is a prayer especially for that. We hope that they turn on him, and they will be heroes if they do."

He added, "Gadhafi has played the tribe game too much."

Even in contemporary Libya, where much of the population now lives in or near cities, many identify as strongly with their tribe as they do with their country, social scientists and many Libyans say. A Libyan who learns that a new acquaintance hails from a well-regarded tribe will often shake hands a second time in a extra measure of respect.

If a Libyan is harmed, a tribe may exact vengeance, sometimes beginning a cycle of retaliatory killings. But if a tribe deems a member to be in the wrong, many Libyans say, it may simply hand him over, hands bound, with a white cloth draped over him for use as a shroud upon the return of his body.

Gadhafi, the son of a Bedouin herder from the central Libyan coast around Surt, began his rule as a modernizer, determined to abolish the tribes. He redrew district boundaries so they no longer matched tribal territories. He appointed administrative officers who replaced the old tribal leaders. Later, he instituted a system of "peoples' committees" supposed to do away with the need for tribal authority completely.

But he has always practiced the Libyan tribal maxim: "My brother and I against my cousin, my cousin and I against the stranger."

And some scholars, including George Joffe of Cambridge University, a leading authority on Libya and its tribes — argue that Gadhafi's tribal upbringing shaped much of his later political ideas, in particular his vision of a giant participatory democracy ruled from behind the scenes by a kind of all-powerful sheik — namely, himself.

"The nation, then, is a big tribe," Gadhafi wrote in his magnum opus, "The Green Book."

Tribes continued to be a major influence for Libyans, who voted along tribal lines in Gadhafi's peoples' congresses. They fought as tribes for property or political spoils. With the preponderance of economic and political power closely held by Gadhafi and his kin, tribal connections became increasingly critical to social advancement as well — one reason corruption has been endemic to the Libyan system, scholars say.

Finally, in 1993, under pressure from international economic sanctions and an Islamist movement centered in the east, Gadhafi reversed himself and incorporated tribes into the system. He brought them together in local and national Popular Social Leadership Counsels, partly formed to help mediate the disputes that could turn into intra-tribal killing rampages and partly to help bolster his government. The leaders of each tribe signed statements making them formally accountable for the conduct and disciplining of their members as well.

But even the tribes who prospered the most under Gadhafi sometimes questioned the high costs of his governing philosophy, such as the country's economic isolation. Scholars say tribes are always competing for the spoils of the system as well. The Qaddafa, for example, resented the power of the Margharha tribe. And the Warfalla resented their effective exclusion from the Libyan air force, a Qaddafa preserve, Joffe said.

It was in 1993 that a group of high ranking military officers from the Qaddafa and Warfalla tribes hatched a plot to kill Gadhafi on a scheduled trip to the Warfalla stronghold of Bani Walid.

Their plan was discovered and foiled at the last minute, but that turned out to be just the beginning of the trouble. Eager to isolate the perpetrators from the larger tribe, Gadhafi pressured the Warfalla themselves to execute the Warfalla plotters. But in an added gesture of defiance the Warfalla steadfastly refused, ultimately forcing Gadhafi to order the executions himself after a hasty trial in early 1997.

Nor did Gadhafi's vengeance stop there, according to Joffe, who has compiled the definitive history of the event. When the father of a coup plotter inquired about his son's expected release in 2002, Gadhafi security forces beat the father so severely he died the same day. Then Gadhafi forces attempted to disinter the father's body, in an extra gesture of humiliation, so that they could throw it into the sea.

When four members of the family resisted, they too were arrested. One died in custody, one was released after torture and two disappeared. All of their houses were burned to the ground.

"Tribes have long memories," Joffe said in an interview, "and this is just the kind of time when a tribe might try to settle some scores."

That would suit the Warfalla leader who talked of the tribes' hatred for Gadhafi. He predicted a "massive tribal attack" once the Warfalla and neighboring tribes obtained weapons.

When exactly that would be, however, he could not say.