Leonard Bernstein, the most celebrated American-born orchestral conductor of the 20th century and a respected composer in his own right, died less than a week after announcing his retirement because of poor health.

Bernstein, composer of such popular classics as the musical "West Side Story," died Sunday in his New York apartment at the age of 72 of cardiac arrest brought on by progressive lung failure.Less than a week ago, Bernstein announced his retirement from active conducting after a career in which he became one of the century's most visible, exciting and beloved conductors.

A lifelong smoker, who often conducted rehearsals with a cigarette instead of a baton, Bernstein suffered in recent years from severe lung problems that had forced him to cancel many appearances.

His son, Alexander, and the conductor's doctor, Kevin Cahill, were at his side when he died, said spokeswoman Margaret Carson. She said Bernstein's funeral would be private.

Last Tuesday, Cahill had ordered Bernstein to retire from public performing, forcing him to cancel appearances with several of the world's top orchestras. News of his death stunned concertgoers in New York. Members of the New York Philharmonic, which Bernstein led from 1957 to 1969, wept. "We played our hearts out for him," said oboist Jerome Roth of the man who was that orchestra's first American-born conductor.

Zubin Mehta, the departing music director of the New York Philharmonic, said of Bernstein: "For the entire world he was the most unique musician of this century; there is no doubt about it."

Mehta told Israel Radio that Bernstein's televised "Young People's Concerts" taught a generation of Americans about classical music and his hundreds of recordings were household items for music lovers.

Bernstein had conducted in Israel many times over the years and Mehta, who also leads the Israel Philharmonic Orchestra, said, "The passing of Leonard Bernstein is really one of the great shocks for us. He was literally the greatest friend of this orchestra."

As word of the conductor's death spread outside Carnegie Hall, where hundreds of concertgoers had just heard the Shanghai Symphony Orchestra, stunned music lovers stopped on street corners to talk about him.

"He'll always be here," said Kristin Kuhr, director of the Carnegie Hall recital stage. "When you step onto the stage you can feel all the greats who have walked there. Now we can feel Bernstein."

Leslie Gooding, a stagehand, said Bernstein was a "fantastic guy. He used to get up onstage and dance after our New Year's party. He was all right."

He was more than all right. He brought classical music to masses of Americans who without him never would have bothered to listen to Beethoven or Bach, and he brought popular music to an elite who without Bernstein never would have bothered to set foot in a Broadway theater.

His most famous composition was the score for "West Side Story," a retelling of "Romeo and Juliet" set on Manhattan's West Side. Here his classical sensibility meshed perfectly with Broadway and a classic was born.

Known as "the boy wonder" of American music, Bernstein was born into a Russian Jewish family where music was frowned upon. He said that if an aunt had not given his family a piano, he might never have fallen in love with music.

But to his father's chagrin, fall in love with music was what Bernstein did at the age of 10.

He played weddings and bar mitzvahs as a young man and, as an adult, played for 200,000 people in Central Park and for millions watching on television as he performed near the Berlin Wall last December.

There were few conductors as dramatic as Bernstein.

His jumps on stage were known as "Lenny Leaps." His white hair flew in every direction. There was drama in every move he made on stage. He used his baton like a lightning rod.

Music critic Tim Page said Bernstein was the personification of American music. "Bernstein as composer, conductor, pianist, author and educator has had as extraordinary an effect on classical music in America as any other person in our history.

"He was amazing and subjective and an inspired conductor. He also wrote great music for the theater. `West Side Story' is in my opinion one of the great masterpieces of Broadway.

"He brought a new and very enthusiastic audience to classical music. He managed to merge classics with jazz and make distinctly American music."

Joan Peyser, author of a controversial 1987 biography of Bernstein, called him "a tremendous musical presence, a man of enormous gifts. He was everything - a composer, conductor, educator, pianist. In his own mind he was primarily a composer. In the public mind, he was a conductor."

He was also a man of many causes - mostly radical ones. He played a concert at a concentration camp shortly after it was liberated and he was a supporter of the Black Panther Party. Tom Wolfe, the journalist, summed up his espousal of that cause with the damning phrase "radical chic."

In a profession that thrives on decorum, Bernstein won attention for unconventional behavior, even wearing dandelions behind his ears. He often shocked people with outspoken views on such topics as sex, marijuana, the Middle East and U.S. politics.

But music came first in his life.

Few American conductors have won such public attention. His passionate performance of Gustav Mahler's works helped establish the composer's reputation worldwide.

Besides his son, the conductor is also survived by his mother, Jennie; his daughters, Jamie Thomas and Nina Bernstein; his sister, Shirley; and his brother, Burton.

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Utah connection

Leonard Bernstein last appeared in Utah in 1985, conducting the Israel Philharmonic Orchestra. The year before, he brought the Vienna Philharmonic to Symphony Hall. In 1963, with the New York Philharmonic, he recorded a collection of Christmas music with the Mormon Tabernacle Choir.