With the capture this week of top Taliban and al-Qaida figures, the United States may have an extraordinary new opportunity to learn how the international terrorist operation worked and where its leaders are. 

Al-Qaida's head of training operations - a top aide to Osama bin Laden - was being held Saturday at the U.S. military camp in Kandahar, Afghanistan. He is the highest-ranking al-Qaida figure captured since the U.S. campaign in Afghanistan began Oct. 7. 

Among those being held by U.S. officials were the terrorist trainer, Ibn Al-Shaykh al-Libi, and the Taliban's former ambassador, Mullah Abdul Salam Zaeef, a U.S. official said Saturday, speaking on condition of anonymity. 

Both men initially were taken into custody by Pakistani authorities before being returned to Afghanistan. 

The prisoners could help focus the continuing hunt for the supreme leaders of the al-Qaida network and the Taliban regime that sheltered it in Afghanistan. 

``These are important figures: One was close to Osama bin Laden and the other was very close to (Taliban leader) Mullah Mohammed Omar,'' former CIA terrorism analyst Stan Beddington said Saturday. 

``The big question, of course, is: Will they talk? If they are able to talk, I have no doubt whatsoever they will give a lot of information, particularly in the search for bin Laden.'' 

Getting them to talk will be the job of military, CIA and FBI interrogators trained to persuade, cajole, trick or flatter prisoners into giving up information. They will also press the detainees for information about other aspects of the global terrorist network, such as its membership, organization, funding, plans and hide-outs. 

The task is often difficult, however. High-ranking members of such groups are likely to be fanatically devoted to their cause and perhaps better prepared to resist questioning. 

``Many of these people that we're taking control of are very, very dangerous people. They are hardened criminals,'' Pentagon spokeswoman Victoria Clarke said Saturday. ``They're very resilient and they are very desperate. Many of them don't care about dying, and they certainly don't care about taking others with them.'' 

U.S. officials say they already have been helped by interrogations of lower-level captives, however, as well as searches of former Taliban and al-Qaida sites. 

``The information we have gotten has been very fruitful in many cases, and we think we have thwarted attacks,'' Gen. Richard Myers, chairman of the Joint Chiefs of Staff, said Thursday. ``It has led to, if not arrests, to surveillance of terrorist leadership.'' 

Authorities in Singapore announced Saturday they had arrested 15 militants with suspected ties to al-Qaida. The government of the Southeast Asian city-state accused the suspects of plotting terrorist bombings and said some had trained at al-Qaida camps in Afghanistan. 

If he talks, al-Libi could be especially helpful to the United States because he was apparently part of bin Laden's inner circle. Not only was he in charge of al-Qaida's terrorist training in Afghanistan, he was also close to Abu Zubaydah, a bin Laden aide also involved in planning and carrying out terrorist attacks. 

``If al-Qaida has plans for carrying out future terrorist attacks, this man would be involved in that, since he was the trainer,'' Beddington said. 

Prisoners like al-Libi can be helpful even if they don't tell everything they know. Intelligence officials often can learn from limited or cryptic comments by fitting them together with information from other sources. 

``You'll get little pieces of information from everybody,'' retired Maj. Gen. Don Shepperd said on CNN Saturday. ``It doesn't mean everybody has to turn, but every little piece of information goes into a bigger picture.'' 

Zaeef became the public face of the Taliban early in the conflict, denouncing the U.S.-led bombing campaign before video cameras in Pakistan before that country cut off diplomatic relations with the Taliban and ordered Zaeef to stop holding news conferences. 

Zaeef could help U.S. officials determine who to trust in Pakistan's intelligence agency, Beddington said. Pakistani intelligence officials had supported the Taliban as the militia took over Afghanistan, although President Pervez Musharraf removed many Taliban supporters from Pakistan's spy agency after the Sept. 11 attacks. 

Now that the Taliban is all but destroyed, Zaeef may not be as helpful a source, Beddington said. 

``We know a lot of what the Taliban is doing, so I don't think he'll be as useful,'' Beddington said. ``He may be able to give some indications of where he thinks Omar has fled. He also might be able to say whether or not the Taliban is indeed trying to regroup.''