He jumps up to answer the telephone just as his wife Rita enters the room. A slender, dark-haired woman, she is a doctor of neuropsychology at Columbia Presbyterian Hospital and a devoted opera fan. "I'm Mrs. Rudel in the morning," she explains, smiling. She met Julius when they were both at music school. Today, while keeping a close friendship with many of the City Opera's singers, she maintains her own identity to the extent that her medical colleagues sometimes tell her, "I saw you at the opera last night," without realizing that her husband was the conductor. The Rudels have lived on the West Side ever since they were married 36 years ago. "My wife sometimes says we live within mugging distance of Lincoln Center," says Rudel, his eyes twinkling with impish amusement. "But really, we're confirmed Westsiders. I don't think I ever use any form of transportation from here to the theatre, and I don't eat out much, because my wife is a marvelous cook. Time being so of the essence, we prefer to stay at home." The City Opera's spring season continues until April 30. Rudel recommends three shows in particular: _The Saint of Bleecker Street_, _The Turn of the Screw_, and _The Marriage of Figaro_, which he is conducting. "I envy all the Westsiders who have the opportunity to come to us," he concludes. "Our seats in the upper reaches of the State Theatre are the best theatrical bargains in the world." ******** EASTSIDER DR. LEE SALK America's foremost child psychologist 5-5-79 At one time, the name Salk was synonymous with one thing only -- the revolutionary polio vaccine discovered by Dr. Jonas Salk in 1953. In the 1970s, however, another national figure of the same name has emerged -- Dr. Lee Salk, Jonas' younger brother, who is probably the most highly respected and best-known child psychologist in America today. The most successful of his five books, _What Every Child Would Like His Parents to Know_ (1972), has been translated into 16 languages, while his most recent work, titled simply _Dear Dr. Salk_, was published in March by Harper & Row. A soft-spoken, highly energetic man who bears a close physical resemblance to comedian Phil Silvers, Dr. Salk recently invited me to share his thoughts in an interview at his Upper East Side apartment.