A new report from [FBI] inspector general, Michael Bromwich [says] that much of the vaunted laboratory's work was amateurish, and, worse, that lab officials who appeared at trials were overly eager to help the prosecution. It discovered, among other things, substandard performances by the laboratory's explosives, chemistry-toxicology and materials analysis units, forcing F.B.I. officials to review several hundred past and current cases -- including the Oklahoma City bombing case -- to determine how many might have been jeopardized by unprofessional work. The inquiry found numerous instances in which untrained F.B.I. agents had been allowed to take part in scientific work. In some cases lab reports were inadequately documented and exaggerated the evidence against defendants. Supervisors provided only the most cursory oversight, giving their subordinates freedom to reach unsupported findings, which then went unchallenged. Specifically, the F.B.I. apparently offered cooked testimony in at least two major cases. In the 1993 World Trade Center bombing case, an examiner in the explosives lab, David Williams, gave inaccurate testimony that ''exceeded his expertise, was unscientific and speculative, was based on improper nonscientific grounds and appeared to be tailored to correspond with his estimate of the amount of explosive used in the bombing.'' That should have been cause for Mr. Williams's dismissal. Instead he was assigned to the Oklahoma City bombing, where, the inspector general found, he committed ''many of the same errors.''