Pacific Chorale to Sing One of Leonard Bernstein’s Last Works : Tribute: The famed conductor’s Missa Brevis, a difficult and rhythmic piece, will debut in an expanded format Wednesday at the Orange County Performing Arts Center.

One of the last pieces Leonard Bernstein wrote before he died on Oct. 14will be sung by the Pacific Chorale on Wednesday at the Orange County Performing Arts Center in Costa Mesa.

The piece--the Missa Brevis--actually is a rewritten and expanded version of an earlier work, a series of choruses composed in 1955 for a production of Jean Anouihl’s play “The Lark.”

According to the Pacific’s music director, John Alexander, it was Atlanta Symphony Conductor and Choral Director Robert Shaw who gave Bernstein the idea that “The Lark” could be made “into a great Missa Brevis.

“Shaw went back to Bernstein two years ago and brought up the idea again,” Alexander said in a recent phone interview. “That’s what instigated the new composition. . . .

“I was scared we weren’t going to get it in time. We got it in September. It was just off the press. In reality, this is the first performance of the expanded version.”

Alexander described the 14-minute work as the standard Lutheran Missa Brevis, which includes all the parts of the Mass except for the Credo.

The work is scored for chorus, percussion and bells.

“It’s an extraordinary work and typically Bernstein in that there is a tremendous rhythmic drive,” he said. “There are movements that are very chantlike, set against some events that could come out of ‘West Side Story.’

“He uses the choir in percussion effects. It’s very hard to sing. There is a lot of marcato (stressed) and staccato singing, which creates wonderful rhythmic effects. But for singers, a linear line is what people train to sing, not rhythmic passages. The voice works more easily when the music is more horizontally conceived.”

In evaluating the Bernstein legacy, Alexander said, “Bernstein was a man who moved in many different fields. He was first of all a conductor, then a composer, a teacher and a poet. In the ‘Kaddish’ Symphony, he uses his own poetry.

“Anyone who diversifies himself that much is not going to create the best in each field. At the same time, for a conductor, this diversity is exactly what you need. It can bring insight into the music, which is what the role of the conductor is. That’s the reason I feel he is one of the major conductors of the century, and we have the recordings to prove that. . . . That is where Bernstein’s legacy will live.”

As far as Bernstein’s music is concerned, Alexander expresses more doubts. “I think anyone would agree that his compositional style is not consistent,” he said.

“In my estimation, Samuel Barber is a better composer than Bernstein is,” he said. The Chorale also will sing Barber’s Agnus Dei, a choral version of his Adagio for Strings on the Wednesday program.

“Barber is the Brahms of 20th-Century American music, particularly for vocal music,” Alexander said. “He was a baritone and quite an accomplished singer. He knew how to write for voice. He doesn’t experiment in the way Bernstein experiments. That’s why I call him the Brahms--taking the standard classical language that was there and building it to the ultimate.

“Bernstein, on the other hand, goes out on a limb. He mixes music of the theater with his classical background. Any time those type of diverse forms are mixed, you get something unique. Bernstein’s music is unique and will live because of that uniqueness.”