This guide is designed to alert readers to the scope and variety of programming coming up. Listing is not meant to represent blanket endorsement. Viewers are urged to be selective. SATURDAY The Lost Episode of Saturday Night Live (NBC, 11:30 p.m.-1 a.m.) Rosanna Arquette is host for this SNL episode, ``lost'' only when it was postponed because of the last World Series overtime game. SUNDAY
Walt Disney World's 15th Birthday Celebration (ABC, 7-9 p.m.): Bea Arthur and Betty White are hosts for this promotional program for the theme park, which for some reason is paired with the US Constitution. It's an excuse to feature everybody from Dolly Parton to former Chief Justice Warren Burger.
The Gal'apagos: Cold On The Equator (PBS, 8-9 p.m.): Part 2 of ``Nature'' miniseries: a look at the animals that survive in the icy waters surrounding these Ecuadoran islands.
The Christian Science Monitor Reports (check local listings for day and time): Japanese farming: rice bowl at risk.
Monte Carlo (CBS, 9-11 p.m.): First of two-part miniseries (concludes Monday) which features a pre-World War II battle: Joan Collins as a Riviera chanteuse vs. the Gestapo. Trashy, flashy, boring, but aimed at ratings success. MONDAY
Picnic (Showtime/pay cable, 8-10 p.m.) A ``Broadway on Showtime'' production of William Inge's Pulitzer Prize-winning play, starring Gregory Harrison and Jennifer Jason Leigh.
Unnatural Causes (NBC, 9-11 p.m.): John Ritter and Alfred Woodard in a fact-based drama inspired by the Agent Orange controversy. TUESDAY
The George McKenna Story (CBS, 9-11 p.m.): A dedicated principal in an inner-city high school teaches everybody a lesson in learning. Based on a real educator. WEDNESDAY
Candide (PBS, 8-10:30 p.m.): ``Live From Lincoln Center'' presents Leonard Bernstein's musical theater/opera adaptation of Voltaire's classic performed by the New York City Opera.
Matisse in Nice (PBS. 10:30-11 p.m.): Exploring the least-known part of Matisse's work, his 1916-31 sojourn in the south of France, when the impact of Nice's light and pattern affected his paintings. THURSDAY
Brat Farrar (PBS-9-10 p.m.): ``Mystery'' starts a three-part miniseries based on Josephine Tey's novel about look-alikes, an inheritance, and a long-concealed murder.
Our World (ABC, 8-9 p.m.): The period May-July 1943 is remembered by Linda Ellerbee and Ray Gandolf on TV's most relaxed newsmagazine show. Listings are in Eastern Time; other zones may vary. Please check listings for all PBS programs, since local option often results in differing days and times.