From punk to pop to pageantry, Hollywood rediscovers the box office at the end of the celluloid rainbow and unveils more movie musicals than a piano has keys. An upbeat preview of what you'll see and hear, from THE APPLE to XANADU.

The celluloid rock boom began on July 20, when The Blues Brothers, Can't Stop The Music and Roadie opened. Their success or failure - as decided by audiences internationally - will help determine the fate of future musical extravaganzas. One movie which will measure the prospects of other megabuck musicals is Universal's Xanadu, a project with all the "right" ingredients for success. The film fronts a modern singing star, Olivia Newton-John, and a song-and-dance man whose name is virtually synonymous with the American screen musical, Gene Kelly. Xanadu's score, a blend of ballads and rock, was composed by Jeff Lynne of Electric Light Orchestra, who sings five original tunes on the soundtrack. Five additional songs were written for Olivia by John Farrar, producer of her nine albums and author of her hits, Have You Never Been Mellow, I Honestly Love You and A Little More Love.

"Xanadu started off as a roller-disco picture," reveals Lee Kramer, the film's executive producer and Olivia Newton-John's personal manager. "The producer, Larry Gordon, and the Universal executive, Joel Silver, never thought of using stars of Olivia's or Gene's stature. The script came to us through our agents.

"Once we became interested in Xanadu, the project underwent a complete metamorphosis, eliminating disco altogether. We really wanted to make an old-fashioned Hollywood musical. The plot concerns a young man (Michael Beck), whose dream is to build an incredible 'fun' palace. Olivia portrays one of the nine muses from Greek mythology - a kind of angel - who comes down to earth and helps these dreams come true. Gene Kelly plays a musician and nightclub owner. These elements have made the movie something special. Xanadu has an elegance all it's own.

Due to it's whimsical theme, Xanadu will probably escape comparison with other, "grittier," rock-oriented films, but since Olivia Newton-John is the movie's star, it will be matched against Grease.

"It seemed that many critics didn't give Olivia credit for playing any sort of a role in Grease," Kramer recalls. "They felt that she was very lightweight, but when you realize the absurdity of a 29-year-old woman playing an 18-year-old girl, you begin to understand that Olivia actually did very well. Xanadu is a new step for her; an absolutely perfect extension. She comes across as a full-fledged actress. With this film, Olivia will get the acknowledgment she deserves."

Xanadu promises to deliver some spectacular production numbers, choreographed by Kenny Ortega (The Rose, Kiss' last world tour) and Jerry Trent (Movie, Movie). One of the best scenes should be a duet between a swing band and The Tubes.

"It's a '40s/'80s number, a dream sequence where a swing band plays a number with zoot suit dancers while The Tubes play a modern rock song," Kramer explains. "It's like counterpoint. We cut back and forth between the groups until finally they come together and play. The ultimate effect is incredible. We literally have two totally different songs, but with the same base. That scene - in fact, the whole film, due to the complex production numbers was a monster to shoot."