NEW YORK, OCT. 9 -- The most spectacular conducting career in American history ended today with the announcement that Leonard Bernstein has retired from public performance, effective immediately, on doctor's orders.

A notorious chain smoker, even while rehearsing orchestras, Bernstein has had serious difficulty breathing recently because of progressive emphysema, complicated by a tumor and infections in the lungs. He has canceled many public appearances in the past year, including a benefit gala for the Spoleto Festival in Charleston, S.C., which had been devastated by Hurricane Hugo.

Bernstein, 72, has not been hospitalized but was not available to comment on his retirement. His press representative, Margaret Carson, said he plans to save his energy for composing and educational projects after recovering from his present illnesses.

As a conductor, composer, pianist and music educator, Bernstein has been the best-known classical musician in U.S. history and one of the most famous anywhere in the 20th century. In recent years, he has been the most eagerly sought guest conductor in the world and, increasingly, one of the hardest to get. One of the largest audiences in history heard his Christmas concert, broadcast from the Berlin Wall last year, celebrating the wall's destruction.

He has been in the public eye and at the top of his profession since his unexpected debut on Nov. 13, 1943, when conductor Bruno Walter was stricken ill and Bernstein, then 25, stepped in at the last minute to conduct the New York Philharmonic and dazzled the audience and critics. His debut was front-page news in the New York Times the next morning, and he has never left the spotlight.

He was appointed music director of the Philharmonic in 1958 (the first American to hold that position) and directed the orchestra for 11 years before resigning to become the world's most sought-after freelance conductor. Earlier, he had been considered for the music directorship of the National Symphony Orchestra, but instead the board chose Howard Mitchell, a member of the orchestra's cello section.

In recent years, Bernstein has been most closely associated with the London Symphony, of which he is the president, and the Vienna Philharmonic, which he has conducted frequently at home and on tour and with which he has made many recordings. His retirement has forced him to cancel engagements with both these orchestras, as well as the New York and Israel philharmonics.

For years, Bernstein has refused to record in a studio, and his Vienna recordings have had the virtues and problems of his live performances -- a sense of spontaneity and excitement as well as occasional overstatement. His rapport with the Vienna orchestra was so strong that he sometimes simply would stand with his hands at his sides while the orchestra played, guiding the musicians with his facial expressions.

The last time he conducted was at the Koussevitzky Memorial Concert, in memory of his mentor, Serge Koussevitzky, at Tanglewood, summer home of the Boston Symphony in Lenox, Mass. That was on Aug. 19, a few days before his 72nd birthday. After that concert, at which he conducted Beethoven's Seventh Symphony and the four "Sea Interludes" from Benjamin Britten's opera "Peter Grimes," Bernstein canceled a planned tour with the Tanglewood Music Center orchestra, a student ensemble.

Conducting was only a part of Bernstein's multifaceted musical career. He is also a notable pianist (another activity that is being ended on doctor's orders), a music educator whose lecture-concerts in the early years of television were a landmark in the field, and a composer whose works range from symphonies and the musical theater piece "Mass," commissioned for the opening of the Kennedy Center, to "West Side Story" -- one of the most successful musicals in the history of Broadway and possibly Bernstein's masterpiece.

After recovering, Carson said, Bernstein plans to devote his remaining energy to composition.

"Dr. {Kevin M.} Cahill {Bernstein's physician} believes that a continued regime of rest and recuperation offers the best hope for Mr. Bernstein to return to a limited schedule of activity," Carson's announcement said. "As soon as his health allows, Maestro Bernstein will continue his work on a new chamber music piece to be performed next spring, a new musical theater piece he hopes to complete by next summer, several educational projects, several film and recording projects, as well as his memoirs. In addition, he hopes to be well enough to participate in the October 28 Carnegie Hall concert, 'Music for Life.' "