FBI Director Robert Mueller, acknowledging serious lapses in how the FBI mishandled some information prior to Sept. 11, suggested for the first time that investigators might have detected the terrorist plot if they had pursued leads more diligently. Mueller's acknowledgment came amid two new disclosures of what could be missed hints about Sept. 11. The first was a warning from another agency to the FBI that a Middle Eastern country was seeking to buy commercial flight simulators. The second was a memo from an Oklahoma City FBI agent who reported observing large numbers of Middle Eastern pilots and flight students in his area. Neither memo apparently drew much attention at the time. Mueller's remarks came after his announcement of a broad reorganization of the FBI, partly because of its failure to predict the attacks. Attorney General John Ashcroft announced loosened restrictions on domestic spying, handing the FBI authority to monitor Internet sites and libraries. The American Civil Liberties Union has criticized the loosening of restrictions on domestic spying, saying they could renew abuses of the past. Mueller, who took over as FBI director just days before Sept. 11, is the first senior official in the Bush administration to say that counterterrorism investigators might have detected and averted the attacks if they had recognized what they were collecting.