John Field, 69, a former director of the Royal Ballet and Sadler's Wells Theater Ballet companies, died Saturday in London of cancer. He also had been ballet director at La Scala. Born in Doncaster in northern England, he studied dancing in Liverpool and made his first appearances at the age of 17 with the Liverpool Ballet Club. At age 18 he joined the Sadler's Wells Ballet in London and took part in its first wartime tour before joining the Royal Air Force in 1942. After World War II, he rejoined Sadler's Wells and became one of its principal dancers, appearing with Margot Fonteyn and Beryl Grey. In 1956, he was appointed artistic director of the Sadler's Wells Theater Ballet, the second company of Sadler's Wells. Months later Sadler's Wells became the Royal Ballet, based at Covent Garden, with Mr. Field as assistant director. In 1970 when Royal Ballet director Sir Frederick Ashton retired, he was named co-director with Kenneth MacMillan but left the post within a year. From 1971 to 1974 he was ballet director at La Scala in Milan. He then became artistic director of the Royal Academy of Dancing and of the London Festival Ballet. In 1984, he retired and became artistic director of the British Ballet Organization.