Not many people are doctors. Even fewer are opera singers. And even fewer are both. Somehow, Dr. John Vroom, a pediatrician on the staff of the Hospital for Sick Children in the District, manages to be both.

"Helping children that have been in a difficult situation gives you a sense of accomplishment, of honor, of duty . . . but to do Handel, Bach, Mozart," said Vroom, pausing to catch his breath, "is a sensual, spiritual experience that's incomparable." He will make his debut as a Handel Festival soloist Saturday in the Kennedy Center Concert Hall.

For the leading roles, Stephan Simon, the production's music director, has chosen stars of the Met, New York City and Covent Garden opera companies. Vroom, a bass-baritone, will appear in the supporting role of a priest of Jupiter in Handel's "Hercules," a three-act work written in 1745. Handel biographer Paul Henry Lang once proclaimed it to be "the crowning glory of baroque music-drama."

The only current D.C. resident with a solo role in "Hercules," Vroom is unique among the cast because his music is more an "avocation" than a vocation. Could the doctor envision making music his sole pursuit? "I haven't ruled out the fact that it could become full time. It would take an emergence of a singing style and talent. It would't be an easy decision to give up medicine."