A senior American official said that the suspect seemed to fit the description of Mr. Zubaydah and that there was a high likelihood that he is the Qaeda commander.

If confirmed, the apprehension would represent the most significant capture of a Qaeda commander since the United States began its military campaign in Afghanistan, which was aimed at destroying the terrorist network and the Taliban government that gave it sanctuary.

The whereabouts of Ayman al-Zawahri, Mr. bin Laden's second-in-command, and most of the Qaeda commanders, are unknown.

Providing new details about the raids to capture the Qaeda commander, American officials said they were conducted by the Pakistani police, who were joined by agents from the United States's Central Intelligence Agency and Federal Bureau of Investigation.

When Pakistani and American agents closed in on the Faisalabad site, the suspected Qaeda commander tried to escape.

According to the agencies, the group called itself the Abu Hafs al-Masri Brigades, named after a senior Qaeda commander killed in Afghanistan in 2001.

Asked about the whereabouts of Osama bin Laden and his deputy, Ayman al-Zawahiri, Mr. Khan has told interrogators that even the top Qaeda commanders do not know, the Pakistani intelligence official said.

If confirmed, it would be the most significant apprehension of a Qaeda commander since the United States began its military campaign.

Despite the size of the armada, however, not a single Taliban or Qaeda commander has been found.

But senior Navy commanders contend that the huge manhunt has pressured Qaeda commanders to stay in Afghanistan or to try to flee over the rugged mountains into Pakistan, where government troops are watching the border.