Third Wheel / Grandmother's Day / Second String Mom

When Gopher series star Fred Grandy and his fun loving mother (Ethel Merman) begin their irrepressible clowning on a Mother's Day Cruise, his dad feels left out; a middle-aged husband and wife get the surprise of their lives when they discover there's a baby on the way, and a recent bride (Beth Howland) gets an accelerated course in motherhood when she has to deal with her husband's (Ken Berry) strong-willed teen-age daughters (Shelley Juttner and Michele Tobin) when the "The Love Boat" sails on the ABC Television Network, SATURDAY, MAY 12 (9:00-10:00 0.m., EDT). In "Third Wheel," written by Lee Aronshon, Gopher, who has never been close to his conservative father, Elliot Smith (Cummings), asks his mother, Ros (Ms. Merman), to perform a musical number with him for the crew show. Later they both realize they have hurt Elliot, who used to do the number with Ros in college. Maggie O'Brien (Ms. Fabray) learns from Doc that she is pregnant and dreads breaking the news to husband Mac (Nelson), who is elatedly planning a future for just the two of them now that the last of their grown children has left home, in "Grandmother's Day," written by Ann Gibbs and Joel Kimmel. In "Second String Mom," written by Lee Aronsohn, Lee Noble (Ms. Howland) is beginning to lose hope of winning the affection of her stepdaughters when they make a forbidden shore trip and suddenly need her help.