For the first time since the Sept. 11, 2001, attacks, CIA analysts see one of al-Qaeda's offshoots - rather than the core group now based in Pakistan - as the most urgent threat to U.S. security, officials said.

The sober new assessment of al-Qaeda's affiliate in Yemen has helped prompt senior Obama administration officials to call for an escalation of U.S. operations there - including a proposal to add armed CIA drones to a clandestine campaign of U.S. military strikes, the officials said.

"We are looking to draw on all of the capabilities at our disposal," said a senior Obama administration official, who described plans for "a ramp-up over a period of months."

The officials, who spoke on the condition of anonymity to discuss intelligence matters, stressed that that analysts continue to see al-Qaeda and its allies in the tribal areas of Pakistan as supremely dangerous adversaries. The officials insisted there would be no letup in their pursuit of Osama bin Laden and other senior figures thought to be hiding in Pakistan.

Indeed, officials said it was largely because al-Qaeda has been decimated by Predator strikes in Pakistan that the franchise in Yemen has emerged as a more potent threat. A CIA strike killed a group of al-Qaeda operatives in Yemen in 2002, but officials said the agency has not had that capability on the peninsula for several years.

"We see al-Qaeda as having suffered major losses, unable to replenish ranks and recover at a pace that would keep them on offense," said a senior U.S. official familiar with the CIA's assessments.

Al-Qaeda in the Arabian Peninsula, as its Yemen-based group is called, is "on the upswing," the official said. "The relative concern ratios are changing. We're more concerned now about AQAP than we were before."

Al-Qaeda in Yemen is seen as more agile and aggressive, officials said. It took the group just a few months to set in motion a plot that succeeded in getting an alleged suicide bomber aboard a Detroit-bound airliner on Christmas Day.

More important, officials cited the role of Anwar al-Aulaqi, an American-born cleric whose command of English and militant ambition have helped transform the Yemen organization into a transnational threat.

Philip Mudd, a former senior official at the CIA and the FBI, argues in a forthcoming article that the threat of a Sept. 11-style attack has been supplanted by a proliferation of plots by AQAP and other affiliates. "The sheer numbers . . . suggest that one of the plots in the United States will succeed," he writes in the latest issue of CTC Sentinel, a publication of the Combating Terrorism Center at the U.S. Military Academy in West Point, N.Y. In the future, he said, "the Pakistan-Afghanistan border region will not be the sole, or even primary, source of bombing suspects."

U.S. officials said the administration's plans to escalate operations in Yemen reflect two aims: improving U.S. intelligence in Yemen and adding new options for carrying out strikes when a target is found.

The CIA has roughly 10 times more people and resources in Pakistan than it does in Yemen. There is no plan to scale back in Pakistan, but officials said the gap is expected to shrink.