Ameritech Corp. said it sued AT&T Corp. for defamation over statements made by John Zeglis, general counsel and senior executive vice president of AT&T. Ameritech's suit alleges that Zeglis made "knowingly false and malicious" comments to "impede and cast doubt on Ameritech's ability to enter the long-distance market." In speaking at a Salomon Bros. investment conference this month in New York, Zeglis said Ameritech wasn't able to handle and process computer-based information on customer orders for local phone service from AT&T, a requirement for Chicago-based Ameritech to get into the long-distance business, according to the suit filed in federal court. Ameritech is seeking an order requiring AT&T to retract and correct its statements, as well as undetermined compensatory and punitive damages. AT&T called Ameritech's charges "unfounded and silly."