This Sunday is your chance to experience the food and music of the Caribbean without ever leaving the city. It's a Caribbean summer party on the Ellipse with delicious tropical drinks and delicacies to help you forget about the heat. Cool off to the sounds of Haitian, Latin, reggae, calypso and soca music and dance to the beat of a steel band. There'll also be island foods such as peleau, barrah, roti, currant rolls and assorted curries. Beverages include sorrel (herb juice), ginger beer and mauby, a thirst-quenching specialty made from tree bark. It all happens on the Ellipse at 15th and Constitution Avenue NW from noon to 8. Call 249-1028; free. Not only are the West Indians celebrating on Sunday, but the Piscataway Indians are having a festival, too. The Maryland Indian Heritage Society is sponsoring the annual celebration Sunday from noon to 5 at Cedarville Park in the Brandywine-Waldorf area. Piscataway tribe members will perform tribal songs and dances and there'll be a display and sale of Indian beadwork, weaving and basketry. Native food such as fry-bread and Indian tacos will also be sold. From D.C., take Beltway exit 7A and follow Route 5 to Cedarville Road, turn left, look for the park entrance on the right and follow the road all the way back.