3:51 p.m. CST, November 21, 2011

In Los Angeles to conduct at the Hollywood Bowl in 1955, composer Leonard Bernstein took a break to visit with playwright Arthur Laurents at the Beverly Hills Hotel swimming pool. The two men sat at the edge of the pool, their legs dangling in the water, discussing not just their assorted projects but also that morning's headlines about juvenile delinquent gangs.

The way Laurents put it in his memoir, that poolside conversation jump-started "West Side Story," one of the most accomplished musicals of all time. Both men were already intrigued by choreographer Jerome Robbins' idea to rethink Shakespeare's "Romeo and Juliet" as a contemporary musical, and the collaborators soon scrapped Catholic and Jewish protagonists for a tale of rival urban gangs.

"West Side Story's" Jets and Sharks burst onto Broadway in 1957, then onto the big screen in 1961. Robbins and Robert Wise directed Natalie Wood and Richard Beymer as the doomed lovers, and the film won 10 Academy Awards, including best picture. A supporting cast led by Rita Moreno, George Chakiris and Russ Tamblyn sang, danced and fought its way across New York's Upper West Side to Bernstein's extraordinary music, Laurents' tender book and Robbins' incomparable choreography; then-27-year-old Stephen Sondheim crafted the memorable lyrics.

To honor the film's 50th anniversary, the Chicago Symphony Orchestra next weekend will present a newly remastered HD film screening and a live performance of Bernstein's music, with David Newman conducting. The original vocals and dialogue from the soundtrack will be left intact; only the live symphonic accompaniment will be new.

The film and reconstituted score also have been presented in New York and Los Angeles, and the project's European premiere will be in London next June.

For the first time since 1961, the project makes it possible for an orchestra to play the complete score, said Garth Edwin Sunderland, senior music editor at the Leonard Bernstein Office in New York. "Until now, the only way a symphonic orchestra could play this music was to play excerpts from the Broadway score or 'Symphonic Dances From "West Side Story,"' a 20-minute concert suite of the dance music."

It was not an easy task for the people who put together the 90-minute score. For the Leonard Bernstein Office, which works to protect and preserve Bernstein's legacy, it was a complicated, multiyear endeavor.

"This is something I wanted to do for quite a while," said Paul Epstein, senior vice president of the Leonard Bernstein Office. "The experience of having a live orchestra is so much more visceral than hearing the soundtrack of a film. With the 50th anniversary of the film coming up, we reinvestigated how to overcome all the obstacles."

The organization, which is the event's producer, had long faced two challenges: Substantial parts of the film's score were missing and, until very recently, there was no good way to separate the film's vocal and orchestral tracks. How would an audience be able to hear the film's vocals without hearing the filmed orchestra?

First was the problem of locating the film music, an endeavor that took Bernstein staff member Eleonor Sandresky a year of research. But even that didn't net a complete orchestral score, explained Sunderland. "For instance, there were not just changes made by the film editor after the recording sessions but also improvisations by studio musicians," he said. "In some places, too, the film orchestration was unwieldy for live performance without the limitless resources of an MGM recording studio."

A major challenge was finding a balance between Bernstein's original orchestrations and the film's elaborations upon them, Sunderland said. "There were 30 seconds in the prologue, for instance, which had five xylophones, doubled by five pianos. It's a thrilling section but completely impractical for live performance."

Ask Sid Ramin, "West Side Story's" Oscar-winning co-orchestrator. "On Broadway, we used 'doublers' for the woodwinds, where the first reed might play flute, clarinet, as many instruments as he knew how to play," he recalled. "But when we did the picture, it was one player for every instrument. I think we used 16 woodwind players rather than the four we had on Broadway. It was a luxury, and we loved it."

Conductor Newman reviewed the evolving score as Bernstein Office staff members assembled their jigsaw puzzle. "Leonard Bernstein's music is so inventive and cleverly done, moving the story forward," said Newman, who has long conducted live music for film projects at the Sundance Institute and the Hollywood Bowl. "Restoring film scores is like a treasure hunt, and I think this score is one of the jewels of the 20th century.

"Bernstein was such an unusual artist," he said. "At the time he wrote this, he was straddling musical theater, symphonic conducting and serious musical composition. I think in 'West Side Story,' he combined popular music, musical theater and opera idioms and turned them into a unique work of art. There was certainly nothing like this in musical theater before."

Steve Linder, senior vice president of global arts manager IMG Artists and the event's production supervisor, was impressed by Newman's enthusiasm and experience. "You have to conduct the score at the same tempo it was done in the original recording," Linder said. "There's very little room for interpretation here. Johnny Green conducted the original score, and you're conducting Johnny Green's original tempos. You're also accompanying vocals and it's a syncing challenge. When you're looking at a film performance, Rita Moreno can sing that song 15 times and she's going to sing it the same way every time."

Technicians were simultaneously taking apart the film's vocal and orchestral tracks. "Traditionally, in motion picture mixing, you have the dialogue track and vocals mixed and kept separate from the final music and sound effects," said Robert Heiber, vice president audio at Burbank-based Chace Audio by Deluxe. "In 'West Side Story,' the orchestra is married to these vocals."

Working with new technology from Paris-based Audionamix, Chace strove to pull off what Heiber calls "an audio magic trick of the highest order." Chace and Audionamix tested their new process first on the film's song "America," a colorful musical number arguing the virtues and follies of Puerto Rico versus America; the song has not just traditional song and dance, but also complicated group vocals, large orchestrations, footsteps and finger snaps. When that worked well, highly trained technicians went on to extract all the music from the film's soundtrack and leave behind the voices and sound effects.

The project comes amid a gaggle of 50th anniversary celebrations. The film was a highlight of the TCM Classic Film Festival in May; writer Misha Berson's new book, "Something's Coming, Something Good: West Side Story and the American Imagination," came out in June; and a Blu-ray version of the film debuts in November.

"One can only imagine Bernstein's music played live by a brilliant orchestra and a conductor sensitized to what Bernstein wanted," said playwright-actor-musician Hershey Felder, whose "Maestro: The Art of Leonard Bernstein," is playing at the Royal George Theatre through Dec. 30. "When musicians are present, there is a deep connection with the audience. I don't know what happens exactly, but as great as a recording is, it never captures the true immediacy of sound leaving an instrument and going right through the listener's body."

Tribune critic John von Rhein contributed.

'MGM HD presents "West Side Story"'

When: 8 p.m. Friday and Saturday, 3 p.m. Nov. 27

Where: Symphony Center, 220 S. Michigan Ave.

Tickets: $41-$151 (limited availability Friday); 312-294-3000, cso.org