The U.S. faces a formidable and invisible weapon in its campaign to drive the Taliban from power, one that many here say binds the group's leaders more tightly than any government in the world.

The ammunition of that weapon is the concept of "bait," an oath of personal loyalty that top Afghan government leaders have taken in allegiance to Mullah Mohammed Omar, the reclusive Taliban leader and protector of Usama bin Laden. And it is no ordinary pledge of political allegiance.

"It is a powerful and absolute ideological concept in Islam. It means that to be good Muslims, the leaders sworn to him must maintain their allegiance," said Sultan Siddiqui, a Pakistani columnist and expert on the Taliban. "They have no choice but to obey."

Some Islamic scholars believe bait binds leader and follower together forever, and can be severed only by the death of the leader. Extremists even argue that breaking the pledge while both are alive could be punishable by death.

Others insist the bonds are not irrevocable. But many concede those who break them run the risk of losing face among their followers.

"Backing out of the bait would be read as a sign of weakness, something that would not go unchallenged," said one Pakistani analyst. "For many here it would be political suicide."

Many in the U.S. may find the bait concept difficult to understand, given the relatively fluid nature of American political alliances. But the tradition dates back many centuries in this part of the world.

"It is a tribal tradition which predates Islam," said Anwar Ahmad, a Pakistani academic who has written extensively on the current crisis. "When a person was nominated as the local chief, he invited tribal elders to 'do bait on his hand.' If he obtained majority support, his nomination was confirmed. Otherwise, either a dispute broke out or another person was nominated."

Ahmad compared the ancient bait to the modern-day process of a prime minister seeking a vote of confidence from parliament. The tradition was carried into Islam after Mohammed's death, and was used to confirm the legitimacy of the caliphs who followed.

But the bait was not meant to be irrevocable, Ahmad maintained, nor was it meant to be used by leaders who abused their powers.

"Even obedience to the caliph is conditioned upon his following a just, honest and equitable path — just as an elected ruler lasts as long as he/she delivers it," he said. "If, however, a group chooses to turn bait into an oath of allegiance — 'till death do us part,' it may find sanction from its tribal ethos — and not necessarily Islam."

Any oath taken in the name of Islam to do something "un-Islamic" voids the covenant, said Ahmad. That means bait could never be used to justify an act of terrorism like those perpetrated on Sept. 11, for example, but could be used later as part of a pact to resist attacks from foreign forces.

That leaves the U.S. to deal with the Taliban bait in a number of ways, according to experts here.

First, the Americans can target Omar himself in the hope his death would scuttle the tight allegiances he has formed with his top leaders. There is already some indication that is happening: One of Omar's homes was bombed in the early days of the U.S. campaign, and U.S. officials confirmed some of his relatives may have been killed when bombs blew up one of his cars over the weekend.

"We're not generally in the business of going after individual leaders. But there's no denying it becomes much easier if Omar is gone, both in terms of getting bin Laden and pushing the Taliban from power," said a diplomat with a NATO country.

Sources said the U.S. is also focusing on driving a wedge between Omar and the various tribal leaders and others who have allied with him, but are not bound by the bait. Experts say no more than about half of the Afghan government's 65,000 troops are bound by the oath, and that defections among the remaining ranks are already widespread.

"Those who are the real Taliban will stay. The others may run off or even join some of the other forces who are fighting against the Taliban," said Saddiqi. "They have not taken the oath, and there is nothing tying them to the Taliban."

Officials have privately admitted that U.S. and Pakistani intelligence officers are working on various schemes to split the Taliban leadership and isolate Omar and his closest supporters. The Pakistanis played a key role in Omar's ascension to power, and may know exactly what is needed to bring him down.

That's particularly important because the U.S. has little hope Omar can ever be persuaded to turn over bin Laden or make any significant moves against his Al Qaeda network. Intelligence reports note that Omar — younger, less educated and lacking the political savvy of bin Laden — is a much a protégé as a contemporary of the accused terrorist mastermind.