New Ballet Master: The New York City Ballet's School of American Ballet has formally announced the appointment of Robert Lindgren as president. Lindgren succeeds Lincoln Kirstein, who co-founded the school with George Balanchine in 1934. Kirstein announced last week that he would retire from both his positions, as president of the school and as general director of the New York City Ballet. Lindgren, who danced under Balanchine, has been with the School of American Ballet since 1987 as executive vice president. Lindgren has also performed in Ballet Theater with the Ballet Russe de Monte Carlo. After retiring from his dancing career, he established a ballet school in Phoenix with his wife, Sonja Tyven, also a former dancer with the New York City Ballet and the Ballet Russe. Lindgren will have responsibility for all administrative functions. Peter Martins will continue as chairman of the faculty.