Al Qaeda's leaders have all but abandoned their former stronghold of Afghanistan, leaving Taliban leader Mullah Mohammed Omar and his followers to deal with the U.S. forces hunting them, Bush administration officials say.

Many of Al Qaeda's surviving leaders relocated to Pakistan, and others went elsewhere in the world, officials said Tuesday.

Usama bin Laden himself remains a mystery. The U.S. government does not know whether he is alive or dead and has little evidence suggesting either possibility.

About a dozen of bin Laden's chief lieutenants have been killed or captured, but more than half have escaped. Officials have identified between 15 and 20 more as their ``most wanted'' members of the group's leadership who are still at large.

Most of the recent captures of Al Qaeda figures have been outside of Afghanistan. In recent months, U.S. officials acknowledged the capture of two: operations chief Abu Zubaydah in March in Pakistan, and operational planner Abu Zubair al-Haili in June in Morocco.

Most of the leadership has been maintaining a low profile to avoid detection, said a U.S. official, speaking on the condition of anonymity.

U.S. counterterrorism officials say chief among their most wanted Al Qaeda are top bin Laden deputy Ayman al-Zawahri, financial chief Shaikh Saiid al-Sharif and operational planner Khalid Shaikh Mohammed, suspected mastermind of the Sept. 11 attacks and the April 11 bombing of a synagogue in Tunisia.

American troops hoped early this month that they were on the trail of one-eyed Taliban spiritual leader Omar, who, like most others from the routed fundamentalist regime, remained in his home country, defense officials said Tuesday.

Omar is believed to be in the mountainous region in or near Uruzgan province in central Afghanistan, but the recent search for him there went horribly wrong.

On July 1, U.S. troops believed they were drawing anti-aircraft fire and responded with AC-130 airstrikes. The gunship was supporting a search for Omar — or others who know his whereabouts — when it struck civilians celebrating a wedding, killing an estimated 40 Afghans, defense officials said Tuesday.

U.S. special forces, teamed with Afghan allies, were pursuing intelligence tips suggesting Omar, at least one of his top commanders or some other Taliban or Al Qaeda figure, was near, officials said.

``They thought (Omar) was in the area,'' said U.S. Army spokesman Gary Tallman at Bagram Air Base in Afghanistan. ``Multiple intelligence sources led us to that conclusion.''

The Pentagon previously refused to say why troops were in the area that night.

Though the Pentagon has been secretive about identifying those captured, some of those killed or captured have been identified:

• America and its allies say they've captured or killed 12 Al Qaeda leaders since Sept. 11. Top among those is bin Laden's military commander, Mohammed Atef, killed by an airstrike in November.

• Suspected Al Qaeda fugitives captured in Pakistan in the past two weeks may include a senior official, Defense Secretary Donald H. Rumsfeld said Monday.

—Several Taliban leaders are in custody, including Mullah Fazel Mazloom, army chief of staff; Mullah Abdul Wakil Muttawakil, minister of foreign affairs; and Mullah Abdul Salam Zaeef, ambassador to Pakistan.

—Taliban intelligence chief Qari Ahmadullah was killed by U.S. bombing Dec. 27.

While most of the Taliban still wanted by the United States are thought to remain in Afghanistan, a few may have gone to Pakistan. They include top Omar aide Tayeb Agha, former Minister of Frontier Affairs Jalaluddin Haqqani and former military commanders Mullah Baradar Akhund, Akhter Mohammed Osmani and Mullah Dadullah.

Coalition forces have been in Uruzgan for months trying to root out Taliban and Al Qaeda holdouts. Much attention also has been given to the southeastern provinces of Paktia and Paktika along the Pakistan border.