Hunting for Osama bin Laden, the CIA established a series of small, covert bases in the rugged mountain frontier of northwest Pakistan in late 2003. Bin Laden, the terrorist leader, was being sheltered there by local tribesmen and foreign militants, the agency had concluded, and he controlled a group of handpicked operatives dedicated to attacking the United States.
But since the bases opened, the CIA officers stationed there have been strictly supervised by Pakistani officials, who have limited their ability to operate and have escorted them wherever they travel in the Pakistani border region. As a result, it has been virtually impossible for the Americans to gather intelligence effectively, say several officials familiar with the operation who would speak only anonymously.
More than three years after the Sept. 11 attacks on the Pentagon and New York transformed bin Laden into the most wanted man in the world, the search for him remains stalled, frustrated by the remote topography of his likely Pakistani sanctuary, stymied by an al-Qaida network that remains well funded and highly disciplined, sidetracked by the distractions of the war in Iraq, and, perhaps most significantly, limited by deep suspicion of the United States among Pakistanis.
Prodded by the United States, Pakistan began an offensive along its northwest border this spring to flush out al-Qaida forces that had escaped from Afghanistan and to help find bin Laden.
But after suffering heavy casualties and causing civilian deaths that stirred opposition, the Pakistani army declared victory two weeks ago and announced that bin Laden was not in Pakistan.
Many U.S. intelligence officials are confident that he is, and that he is as dangerous as ever.
The war in Afghanistan inflicted severe damage on al-Qaida, forcing it to adapt to survive, intelligence specialists agree. Today, they say it largely functions as a loose network of local franchises linked by a militant Islamist ideology. But bin Laden remains much more than just an iconic figurehead of Islamic militancy, most U.S. intelligence officials now say. From a presumed hiding place on the Pakistani side of the Afghan-Pakistan border, he controls an elite terrorist cell devoted to attacking the United States, the officials say they suspect. They contend that he personally oversees the group of al-Qaida operatives, which he hopes to use for another "spectacular" event, like the Sept. 11 attacks.
U.S. counterterrorism analysts say this unit probably is dispersed, though they do not know where. This "external planning group" can communicate with regional affiliates around the world to work with them when needed, one senior intelligence official said. "There is a strong desire by bin Laden to attack the continental United States, and he wants to use the external planning mode to do it," the official said.
But the United States has failed to penetrate the group and has no idea when or where it will try to strike, the officials acknowledged. The contention of intelligence officials that such a group poses grave danger helps explain why the Bush administration continues to respond so strongly to reported terrorist threats; officials cannot tell which ones to take most seriously.
Intelligence officials would not provide any details of how they reached their conclusions about bin Laden's current role.
Many analysts are convinced that he is being protected by a well-financed network of Pakistani tribesmen and foreign militants who operate in the impoverished border region, and that they have helped him communicate with major figures in his network.
"Bin Laden is getting his logistical support from the tribes," said one intelligence official. "He still has operational communications with the outside."
The place suspected of being bin Laden's hideout, in the shadow of the Hindu Kush mountain range, is in one of the most isolated and backward corners of the world.