No matter the ultimate determination, administration officials said they were bracing for the possibility that the tape might contain hidden messages to Qaeda followers, and that these might spur further terrorist attacks.

But the official said it was not yet clear whether the men were Qaeda followers or might belong to other Islamic militant groups.

The C.I.A. identified 30 locations that might be targets of an attack and sought to disrupt groups of Qaeda followers.

When one low-level Qaeda follower was arrested in Karachi, the police found what they said was evidence that the apartment had been used by Mr. Mohammed.

The Khan computer files also led to the arrest of 11 Qaeda followers last week in Britain.

The C.I.A. document identifies four Qaeda followers in Baghdad, described by one official as "second- or third-tier leaders."

Intelligence officials said that some of the Qaeda followers in northern Iraq had fled there from the war in Afghanistan, and were not thought to be under the control of Mr. Zarqawi.

Speaking of Qaeda followers in the United States, Mr. Mueller said: "The focus of their activities centers primarily on fund-raising, recruitment and training.

People who have read the memorandum said it did not identify anyone by name as a Qaeda follower, did not specify which flight schools should be investigated or explicitly predict the Sept. 11 attacks.

Government officials would not identify the Qaeda follower to whom Mr. Ashcroft and other officials referred today as the principal source of information about the possible attacks.