Is "network bashing" the latest weapon in television's ongoing ratings wars? Both "Designing Women" and "Cagney & Lacey," airing back-to-back on CBS Monday night, ribbed programs carried by ABC and NBC with throw-away jokes unrelated to the plots. During an otherwise serious "Designing Women" episode on AIDS, a secondary character took a shot at ABC's "Max Headroom," saying that "Larry Hagman is a much better actor." ("Dallas" airs opposite "Max" on Friday nights). On "Cagney & Lacey, Mary Beth Lacey (Tyne Daly) fired a barb at "L.A. Law" heartthrob Harry Hamlin, declaring that Hamlin, unlike the "good-looking" lawyer who defended Lacey against a police misconduct charge, never smiles in court. A CBS spokesman denied Tuesday that the network was engaged in any kind of orchestrated campaign to bash its competitors' programs. "We have nothing to do with the writing of the scripts," he said. "The fact that two consecutive shows took potshots at the other networks is pure coincidence."