Little Billy Crystal, who played Jody on "Soap," is thoroughly upstaged by his guest stars on the premiere of NBC's interim series "The Billy Crystal Comedy Hour," at 10 tonight on Channel 4. The guests are Robin Williams and three members of the miraculously inventive "SCTV" comedy troupe: John Candy, Dave Thomas and Rick Moranis.

Crystal delivers his tailored stand-up material capably enough, but it's really comedy-club stuff -- literally not ready for prime time. Then, boomski-boomski, Williams appears like an insanely generous Santa, and instantly the hour is kicked into life. Despite the failure of "Mork and Mindy," Williams is still a comedy colossus; he's a whole pharmacy of brainstorms and references. He's as fascinating as heat lightning and just as hard to predict.

In the hour's only appealing sketch, Williams and Crystal play two bitchy Las Vegas dancers who have to rehearse "Betty and the Boys" without Betty. Williams is wonderful, just wonderful; he may have the most dangerous glint in comedy history, and he still seems absolutely delighted with the fact that he is allowed to roam the earth in relative freedom.

Candy, Thomas and Moranis show up individually, doing three of the living parodies they have practiced to perfection on "SCTV," the best comedy show on television. The Thomas version of Bob Hope is now a much more welcome sight on the screen than Hope himself. Moranis has nailed Woody Allen to a tree. And Candy's Orson Welles, though not really an accurate vocal impersonation, is faithful in mind and body; "Welles" does one of those endless and indecipherable magic tricks that got him kicked off the roster of "The Tonight Show."

"I had a great time tonight," Crystal assures us at the end of the hour, as if the audience were there to win his approval instead of the other way around. Crystal's repeated allusions to show business and how naturally he has taken to it could turn him into the very worst kind of bore, especially when he is surrounded by gifted funsters who seem to realize just how phony it all is.