WITH "ANNIE" already established as one of the bigger hits on the Broadway stage, the arrival of "The Rescuers"—the first animated feature from the Walt Disney organization since 1973—could make this the year of the transcendent orphan. Like Little Orphan Annie, Penny, the small heroine of "The Rescuers," is parentless and subject to all sorts of evil designs by people, who fortunately, are so incompetent that they are virtually self-destruct mechanisms."The Rescuers," which opened yesterday at the Cinerama Two and other theaters, is efficiently short, charming, mildly scary in unimportant ways, and occasionally very funny. It's a perfect show for the very, very young who take their cartoons seriously.The screenplay, based on two stories by Margery Sharp, is principally about the efforts of two do-gooding New York mice, Bernard and Miss Bianca, members of something called the Rescue Aid Society, to rescue Penny after she's been kidnapped by a certain Madame Medusa. The last, who runs Madame Medusa's Pawn Shop Boutique, has stolen the child and whisked her off to Louisiana because Penny is the only person small enough to crawl into a pirate's cave there and retrieve a diamond as big as a baseball.I doubt that even small children will pay too much attention to the story, which, as it should be, is simply the excuse for a series of marvelously improbable adventures. There is, for example, the hectic journey that Bernard, whose voice and something of his personality are supplied by Bob Newhart, and Miss Bianca (voice by Eva Gabor) take to Louisiana via Albatross Air Charter Service. The "equipment," as it's called in timetables, is a very tired albatross named Orville who hasn't yet mastered takeoffs or landings.In the Devil's Bayou in Louisiana there are split-second escapes from Madame Medusa, a fine, flame-haired Gorgon for whom Geraldine Page supplies the voice and comic presence, and encounters with various swamp types, including a dragonfly named Evinrude who runs a local boat service.With periodic timeouts for obligatory songs of an especially forgettable nature, "The Rescuers" moves quickly and without fuss from one episode to the next, never creating a sense of any real dread or fear. The animation is pretty in a conventional fashion that may be as fascinating to children as the bold innovations of someone like Ralph Bakshi are to the rest of us."The Rescuers" doesn't belong in the same category as the great Disney cartoon features ("Snow White and The Seven Dwarfs," "Bambi," "Fantasia") but it's a reminder of a kind of slickly cheerful, animated entertainment that has become all but extinct.