"The Dreamer of Oz," an NBC movie airing tonight at 9 on Channel 4, tells the story of a storyteller who took everybody, including himself, by surprise. Appropriately enough, and despite a weak lead performance, the film is surprisingly good.

L. Frank Baum and illustrator W.W. Denslow had some success in 1899 with their first children's book, "Father Goose," but nothing prepared them for the acclaim and popularity that "The Wonderful Wizard of Oz" would achieve when it was published the following year. "Oz" saw the century in and will be around to see it out.

Several silent films and stage plays were made based on "Wizard" and the 13 other "Oz" books Baum subsequently wrote, but the version the world holds dear is the MGM musical starring Judy Garland. "Dreamer" uses that as a jumping-off point; it's a long flashback framed by scenes set at the 1939 world premiere in Hollywood.

One of the most visually attractive films ever made for television, "Dreamer" decorates its straightforward Baum biography with fantasy inserts that show the book and its characters taking shape in the author's head. The special effects, produced with digital animation and other technological tricks, are wondrous to behold.

Of course, no TV movie can compete with the visions that MGM conjured in Technicolor, and NBC's effects are digital rather than cinematic -- CD instead of LP, you might say. But the filmmakers have done a spectacular job just the same, and while the makeup for the Oz characters pales in comparison to Jack Dawn's for the MGM film, the look really is faithful to Denslow's original whimsical drawings.

"Dreamer" is cheerfully satisfying as a lavish footnote to an American classic. The filmmakers appear to have been essentially true to the largely undramatic details of Baum's life. Robert Baum, the author's great-grandson, was a consultant to the producers; he and his wife appear in bit parts as customers at Baum's general store.

Unfortunately, John Ritter, a likable actor but one of criminally limited range, is merely okay as Baum, never quite revealing what drove the man to create an alternative world of witches, Munchkins and flying monkeys.

One assumes Baum fumbled his various adult occupations because he remained to some degree a frustrated, starry-eyed kid. But Ritter doesn't convey this, lacking the kind of man-child charm that Danny Kaye brought to the title role of "Hans Christian Andersen" in 1952. Nor does he play Baum as the kind of hapless daydreamer that James Dunn immortalized in "A Tree Grows in Brooklyn."

He doesn't interpret the role, he just toys with it.

Annette O'Toole is more believable as Maud, who gives up a promising legal career to marry Baum and traipse around the country with him. She's the one who tells their story outside Grauman's Chinese Theater at the '39 premiere. An inquiring reporter tells her, "I'll sit here as long as you want, Mrs. Baum."

Son of a gun, that turns out to be two hours.

Veteran scriptwriter Richard Matheson and director Jack Bender show Baum encountering real-life characters who inspire the colorful cast of his books. Dorothy, the 6-year-old heroine, was based on Baum's niece Dorothy, who died of illness at the age of 6.

A blowhard who challenges Baum to a duel and then chickens out at the last minute becomes the Cowardly Lion, both played by versatile Charles Haid. Baum's crabby mother-in-law, not unexpectedly, becomes the Wicked Witch, played by Rue McClanahan of "The Golden Girls."

And a blustering traveling salesman on a train out of Chicago, dismissed by a colleague as a "humbug," becomes the humbuggy wizard himself. As for the name Oz, Baum improvised that from the label on a file drawer: "O-Z."

What made the book revolutionary in its time was that, as America had done a century earlier, it broke away from Europe. Baum wanted to write an indigenous fairy tale without, he said, "bloodcurdling" incidents or a "fearsome moral." At this he found, at last, success.

"The Dreamer of Oz" is likely to join TV's ever-expanding population of holiday perennials. Although children will be bored by the extensive screen time given to Baum's romance and marriage, there's enough wonder to keep them interested, and thanks to the work of craftsmen behind the scenes, it's gorgeous wonder besides.