The annual Lilac Festival in Rochester, N.Y., is scheduled for May 13-22, 1983. In addition to highlighting the world's largest display of several varieties of lilacs, the 10-day festival will have almost daily entertainment at the downtown festival tent and Highland Park. On hand will be the Harry James Orchestra, as well as other musical groups, orchestras, strolling troubadours, and puppet shows. A teen pageant, ''oldies night,'' high school jazz-band competition, ''battle of the bands,'' and blues night will also be held. For more information, contact the Lilac Festival Committee at the Convention and Visitors Bureau, 120 Main Street East, Rochester, N.Y. 14604; (716) 546-3070.