WARNER Bros is loading up the cast of Wyatt Earp with more familiar big-screen faces than have been assembled for a movie in recent memory. In addition to stars Kevin Costner, Dennis Quaid and Gene Hackman, director Lawrence Kasdan has added Mark Harmon, Adam Baldwin, Tom Sizemore, Mary Steenbergen, Betty Buckley, David Andrews and Linden Ashby. Currently shooting on locations in Santa Fe, New Mexico, Wyatt Earp features Costner in the title role, Quaid as Earp's sidekick, Doc Holliday, and Hackman as the Earp family patriarch. Toronto-based Skyvision Entertainment has opened offices in Santa Monica to produce Robocop: The Series , an action-adventure sci-fi show scheduled to begin filming next month. Betty White, who starred as the pal of Bea Arthur, Estelle Getty and Rue McClanahan in the defunct The Golden Girls series, will join Bob Newhart's overhauled Bob sitcom this season. The Newhart show, which makes its autumn debut late next month, will find Bob running the greeting-card company he left to pursue his comic book career during the show's first season. White will be seen as the wife of the company's former owner. Writer-producer William Peter Blatty and director William Friedkin, who wrote and directed The Exorcist , are joining forces again to make Elsewhere , another supernatural thriller.