''This is a big catch,'' Pakistan's information minister, Sheikh Rashid Ahmed, said. ''We were looking for him for a very long time.''
Pakistani and American officials described al-Libbi as the third most senior leader in al-Qaida's terrorist network.
Pakistani intelligence officials said the arrest came early Monday in Mardan, a town 30 miles north of Peshawar.
The capture appears to be a rare coup for ''human intelligence,'' or old-fashioned spycraft, and may yield details of how the terror network hoped to disrupt last year's U.S. presidential elections.
Offering a peek into how the arrest of al-Libbi came together, U.S. officials largely attributed the capture to successful human intelligence - ''humint,'' in intel-speak - or the classic pursuit of human sources who slip crucial information to U.S. operatives. Sometimes they get paid for it.
For months, if not over a year, U.S. and Pakistani authorities have been working together in a painstaking hunt for the Libyan described as the leading operational planner for al-Qaida. One former senior intelligence official said al-Libbi evaded capture several times last year alone.
The victory for traditional spy techniques comes as the CIA and other intelligence agencies have been publicly chastised in a series of reports for falling down on their human intelligence work in the months leading up to the attacks of Sept. 11, 2001, and the 2003 Iraq invasion.
The arrest provided a much-needed public victory.
''Al-Libbi was a top general for [Osama] bin Laden,'' President Bush said Wednesday. ''He was a major facilitator and a chief planner for the al-Qaida network. His arrest removes a dangerous enemy who was a direct threat to America and for those who love freedom.''
Said former clandestine service chief Jim Pavitt, who left the agency last summer: ''They did this one by sheer perseverance.''
Current and former government officials say U.S. and Pakistani authorities are no doubt interrogating al-Libbi about his knowledge in any pending operations - and past ones. Hopes are high that he will have information.
Former intelligence officials expect the Pakistanis to be most interested in acquiring details about two unsuccessful assassination attempts in December 2003 against their president. Al-Libbi is a main suspect in those attacks against a leading U.S. ally.
Yet U.S. counterterrorism officials are also interested in his possible role in a wide variety of operations in Pakistan, Afghanistan, Europe and beyond, where al-Libbi is believed to be coordinating the movement of fighters and other logistical and planning activities.
One counterterrorism official, who spoke on condition of anonymity, said there is a consensus forming that al-Libbi played a role in the pre-election threat that had American officials on guard in the months leading up to November 2004. Officials have since acknowledged that at least one source of the early information was deemed not credible. The attack never came.
Al-Libbi is hardly a dinner-table name. With his arrest, a picture of the terrorist who rose al-Qaida's ranks is beginning to take shape.
U.S. officials said al-Libbi's association with bin Laden goes back to al-Qaida's early days in Sudan, where bin Laden set up a complex of businesses and terror enterprises in 1991.
Al-Libbi joined bin Laden in Afghanistan, where he functioned as a trainer in some of the al-Qaida-run camps. Well-connected and involved in supporting operations and fundraising, al-Libbi had a hand in supporting the Taliban in the late 1990s.
He is also believed to have taken over as the group's senior operational planner sometime after U.S. and Pakistani authorities rounded up the 9-11 mastermind Khalid Shaikh Mohammed - also known as KSM - in March 2003.
Former CIA counterterrorism chief Vince Cannistraro said al-Libbi is less worldly than KSM, who presided over a tidier pre-Sept. 11 network of operatives and al-Qaida base camps in Afghanistan.
Yet current and former U.S. government officials universally applauded al-Libbi's arrest - particularly because of his suspected role in trying to kill Musharraf - even as some wondered aloud whether his importance was being inflated.
It's also unclear how much al-Libbi will know about some the U.S. government's most-wanted suspects - bin Laden and his deputy, Ayman al-Zawahri. Nearly four years after 9-11 and dozens of captures later, they both remain at large.
