The Louisville, Ky.-based Humana Inc. hospital chain has filed a federal suit against NBC-TV, claiming the network is infringing on the company's trademark in its Emmy award-winning show "St. Elsewhere." The suit, filed Tuesday in Louisville, asks that NBC immediately stop using the name "Ecumena" for the fictional hospital that is the basis of the show's story line. No specific monetary damages were cited in the suit. NBC "believes the complaint is totally without merit," said Ellen Miller-Wachtel, an attorney for the network.