Attorney General John Ashcroft said the federal authorities had identified 18 men who hijacked the commercial jets used in Tuesday’s attacks, while investigators accelerated a nationwide manhunt for dozens of accomplices believed to have supported the assaults on the World Trade Center and the Pentagon. Investigators examining records at flight training school in Florida and elsewhere have determined that other people, who may have links to the terror plot but who did not take part in Tuesday’s attacks, received flying lessons at the schools, law enforcement officials said. They said that the discovery of additional pilots who might form the nucleus of more hijacked teams had heightened security concerns in the capital and elsewhere.