Authorities believe the core of Osama bin Laden’s al-Qaida network has been scattered and weakened by the U.S.-led war on terrorism but officials say the number of sympathizers eager to further the cause of Muslim holy war may be growing a year after the devastating attacks of Sept. 11.

While the strong U.S. military presence in Afghanistan crushed al-Qaida’s presence there, U.S. counterterrorism officials say a large number of leaders moved into neighboring Pakistan. Some went into the cities, including bin Laden deputy Abu Zubaydah, who was captured in Faisalabad in March. Others stayed in the remote mountain border area.

Bin Laden’s No. 2, the Egyptian doctor Ayman al-Zawahri, was thought to be in that region as recently as last month, U.S. officials said. The al-Qaida leader’s whereabouts are unknown and the U.S. government has said it does not know whether bin Laden is alive or dead.

About a dozen of his chief lieutenants have been killed or captured, but more than half have escaped. Officials have said that between 15 and 20 senior members of the group’s leadership are still at large.

Some returned to their home countries of Yemen, Saudi Arabia, Syria, Lebanon and Morocco. U.S. and foreign intelligence officials have said there is evidence some al-Qaida fugitives have migrated to Hezbollah, the Iranian-supported guerrilla group which targets Israel from Lebanon.

Al-Qaida’s most active operational leaders now are believed to be Khalid Shaikh Mohammed, whom officials have identified as the mastermind behind Sept. 11, and Abd al-Rahim al-Nashiri.

The Arab satellite station Al-Jazeera said this week that one of its correspondents had interviewed Mohammed and Sept. 11 fugitive Ramzi Binalshibh in June in Pakistan. The interview is scheduled to air today along with a videotape in which the station says bin Laden can be heard naming several of the Sept. 11 hijackers and discussing the attacks.

The war has made it more difficult for al-Qaida to communicate and move money around now that its Afghan base has been wiped out.

But the dispersal has led to what counterterrorism officials describe as a decentralized network of operatives, affiliate groups and individual cells turning to their own devices to plot attacks.

U.S. officials say the result may mean less complicated plots than the Sept. 11 attacks, but experts warn the new situation could complicate the future of the war.

Even worse, others say, is that the new situation gives al-Qaida’s followers an opportunity to recruit in new places and strengthen ties with militant groups fighting for Muslim causes in Bosnia, Southeast Asia and North Africa.