Mary returns with a new format, a kind of show within a show. She plays Mary McKinnon, whose TV variety show provides a vehicle for weekly guests, and a frame for backstage comedy. On the curtain raiser, Mary's attempts to land Lucille Ball on her program land them both on ""The Mike Douglas Show,"" both in a state of advanced inebriation. Lucy and Mary sing ""Girl Friends of the Whirling Dervish.""-TV Guide March 3-9, 1979