Twelve fantasy/horror stories with movie-biz premises--some of them decades old, most of them overextended or laboriously preachy. Time-travel is the preferred film gimmick: C. S. Forester offers a screenwriter with the power to make any wish come true, including his wish to romance a long-ago film goddess (in the effectively brief ""Payment Anticipated""); T. L. Sherred's ""E for Effort"" provides an ingenious notion--a magic camera which can film any moment in history--but stretches it out interminably, with a clumsily well-meaning finale (anti-nuclear war); Jack Finney serves up a vignette in his nostalgic Time and Again style; Robert Bloch's ""The Movie People"" are ghostly extras who live forever, appearing in crowd scenes through films of every decade; and Henry Slesar's ""The Movie-Makers"" are aliens who destroy a man by recapturing his past on film. The most effective piece here, however, is not about time-travel. It's Ray Bradbury's ""The Meadow"" (1948), which remains a model of low-key Message storytelling, with a movie-studio lot (where countries and cities overlap) as a plain, haunting metaphor for an ideal world. (In contrast, Howard Fast's movie-house-as-metaphor is crude, and Robert Sheckley's ""The Never-Ending Western Movie"" is murkily pretentious.) The motley remainder: Thomas M. Disch's effortful send-up of the underground-flick scene; Robert Silverberg's ""Reality Unlimited,"" a dated (1957) parody of the Cinerama/ Smellerama craze; a third-rate horror episode by J. Michael Reaves; Gahan Wilson's amusing one-page ""Horror Movie Pocket Computer""; and Ben Hecht's 1939 ""The Missing Idol'--an overlong, overdone, yet often hilarious satire on the crass making of a Biblical film (with God mucking up the shooting schedule). A few worthy rediscoveries, then, but mostly humdrum Twilight Zone-ings.