ISLAMABAD, Pakistan — A Central Intelligence Agency drone strike in Pakistan’s tribal belt killed Al Qaeda’s deputy leader, Abu Yahya al- Libi, American officials said on Tuesday, dealing another blow to the group in a lawless area that has long been considered the global headquarters of international terrorism but the importance of which may now be slipping.

Mr. Libi’s death would be another dramatic moment for an American covert war in Pakistan that has been particularly active over the past year, starting with the death of the group’s founder, Osama bin Laden, in May 2011 and followed up by drone strikes against several senior lieutenants, including Atiyah Abd al-Rahman.

But that very success could, paradoxically, signal a shifting target: as Al Qaeda’s leadership in the tribal belt has been cornered or killed, new efforts to attack Western targets have been mounted by the group’s affiliates in Yemen and Somalia.

Unlike many of the relatively unknown figures killed in other drone strikes, Mr. Libi, who had a $1 million bounty on his head, was a virtual ambassador for global jihad. An Islamic scholar by training, he used frequent video appearances to expound on world events, chastise critics and boast about his escape from an American military prison in Afghanistan in 2005.

He negotiated with the ethnic Pashtun militant groups that have sheltered Al Qaeda in the tribal belt for over a decade, and at one point urged Pakistanis to overthrow their own government.

The White House spokesman, Jay Carney, said that as a result of Mr. Libi’s death, “there is no clear successor to take on the breadth of his responsibility, and that puts additional pressure” on Al Qaeda, “bringing it closer to its ultimate demise than ever.”

The details of his death in Hassu Khel, a village in the North Waziristan tribal agency, remained hazy. And it is not the first report that he has been killed: rumors of his death coursed through jihadi Web sites in December 2009 after a similar strike in South Waziristan that American officials claimed had killed a high-ranking figure in Al Qaeda.

If his death is borne out this time, it would be a milestone in a covert eight-year airstrike campaign that has infuriated Pakistani officials but that has remained one of the United States’ most effective tools in combating militancy.

Local tribesmen and American officials said that a C.I.A.-controlled drone fired on a compound early Monday morning. Word spread quickly among local tribesmen that Mr. Libi had been killed or wounded, and American intelligence officials using powerful satellite and other surveillance equipment listened and watched carefully for a sign of his fate.

Apparent confirmation came late Tuesday, although American officials did not give supporting details. After previous strikes in the tribal belt, the National Security Agency has monitored cellphone, radio and Internet messages to confirm the effects of the missions.

American officials said that Mr. Libi was the only person who died in the attack, although others were present in the compound. A tribesman from the area, speaking by phone and citing Taliban sources, said that three to five militants had been killed. But he agreed that no civilians had died because there had been no public funerals in the area.

Mr. Libi, who was thought to be in his late 40s, was born in Libya, and during the 1990s he was a member of an Islamist group that sought to overthrow Col. Muammar el-Qaddafi.

His star rose after he escaped from a United States military detention center at Bagram Air Base outside Kabul in July 2005, picking a lock and dodging the prison guards, along with three other Qaeda operatives.

A year later, Mr. Libi released a 54-minute video mocking his American captors — the first of many that would burnish his reputation as a propagandist.

After Bin Laden’s death, Mr. Libi moved up to become Al Qaeda’s deputy, behind Ayman al-Zawahri.

One American official, speaking on the condition of anonymity, described Mr. Libi as one of Al Qaeda’s “most experienced and versatile leaders,” and said he had “played a critical role in the group’s planning against the West, providing oversight of the external operations efforts.”

Another American official said: “Zawahri will be hard-pressed to find any one person who can readily step into Abu Yahya’s shoes. In addition to his gravitas as a longstanding member of A.Q.’s leadership, Abu Yahya’s religious credentials gave him the authority to issue fatwas, operational approvals and guidance to the core group in Pakistan and regional affiliates. There is no one who even comes close in terms of replacing the expertise A.Q. has just lost.”

Some independent experts, however, were more cautious. “Killing the top leadership harms Al Qaeda, but it won’t defeat them,” said Bill Roggio of the Web site Long War Journal, which tracks drone strikes in the tribal belt, among other topics. “There are people who will step up to fill the void. Al Qaeda has a far deeper bench than the administration gives it credit for.”

Mr. Roggio said that while drone strikes offered an attractive short- term tactic against Qaeda militants, they did not present a complete strategy. “Until we tackle Al Qaeda’s ideology, state support and ability to exploit ungoverned space in countries like Pakistan, Somalia and Yemen, you’re not going to defeat the organization,” he said.

Mr. Libi’s death also raises questions about the center of gravity of Al Qaeda’s global operations. In 2007, the National Intelligence Estimate, a document produced by 16 American intelligence agencies, declared that the tribal belt had become Al Qaeda’s global headquarters. Yet in recent years, some of the most dangerous plots have come from its affiliate in Yemen.

Umar Farouk Abdulmutallab, the young Nigerian who tried to detonate a bomb in his underwear as an airliner approached Detroit in December 2009, was trained in the mountains of Yemen. Last September, an American drone attack 90 miles east of the Yemeni capital, Sana, killed Anwar al-Awlaki, an American preacher and jihadist recruiter, and Samir Khan, an American citizen of Pakistani origin.

Some American officials consider Mr. Awlaki’s death to be at least as significant, in counterterrorism terms, as the killing of Mr. Libi. Even in death, Mr. Awlaki’s archived exhortations for jihad are considered a potent force.

Still, Pakistan’s tribal belt remains a hub of regional and international militancy. Faisal Shahzad, who tried to explode a car bomb in Times Square in May 2010, said he had received explosives training from the Pakistani Taliban. Insurgent fighters based in Waziristan regularly attack NATO and Afghan forces in Afghanistan and have been targeted by C.I.A. drones. And Mr. Zawahri, the Qaeda leader, is widely believed to be in Pakistan.

But the strikes are intensely contentious among Pakistan’s political and military elite. In April, Pakistan’s Parliament passed a resolution demanding that the drone campaign immediately stop, but the tempo of strikes picked up greatly after negotiations to reopen NATO supply lines through Pakistan to Afghanistan bogged down last month.

A senior Pakistani security official said that Pakistani intelligence had no independent confirmation of Mr. Libi’s death. Even if it was proved, he added, his country’s opposition to the drone campaign would not change.

“Practically speaking, the drone strikes are a big success. But strategically they are a huge loss. They create more polarization, more enemies, and are an attack on our sovereignty,” he said. “We have always told the Americans that if anyone should carry out these strikes, it should be us.”

Other Pakistanis say that Al Qaeda should simply leave their country. After Mr. Libi’s death was announced, Tazeen Jay, a blogger, wrote on Twitter, “I long for the day when they die elsewhere, not in Pakistan.”

Declan Walsh reported from Islamabad, and Eric Schmitt from Washington. Ihsanullah Tipu Mehsud contributed reporting from Islamabad, and Jackie Calmes from Washington. (Copyright 2012 The New York Times Company 06/06/12)