Government lawyers say the ongoing investigation into the Sept. 11 attacks could be compromised if the airline industry is allowed to seek more information from the FBI to defend itself against lawsuits brought by terrorism victims. The government urged a judge to block aviation companies from interviewing five FBI employees who the companies say will help them prove the government withheld key information before the 2001 attacks. The lawyers said it would be impossible to interview the employees without disclosing classified or privileged material that could cause serious damage to national security and interfere with pending law enforcement proceedings." The largest investigation in FBI history has resulted in 167,000 interviews and more than 155,000 pieces of evidence and involved the pursuit of 500,000 investigative leads, the lawyers wrote. The airlines and aviation companies are defending themselves against lawsuits seeking billions of dollars in damages for injuries, fatalities, property damage and business losses related to the Sept. 11, 2001 attacks. The companies filed separate lawsuits against the CIA and the FBI last August to force terrorism investigators to tell whether the aviation industry was to blame for the Sept. 11 attacks. Meanwhile, lawyers for the victims of the attacks ... recounted in court papers numerous hijackings and attacks aboard planes before Sept. 11 that they said should have put the airline industry on notice that a disastrous attack could occur.