The Sunshine Skiffle Band, one of the area's more singular musical groups, but one whose generic type possibly goes back thousands of years, will perform Saturday night in a double bill with the Federal Jazz Commission, a New Orleans-style band. The event, sponsored by the Potomac River Jazz Club, will be at the Twin Bridges Marriott in Arlington at 9 p.m.

Gil Carter, leader of the 3-year-old group, explained its genesis: "It came about because I had an instrument called a rhumba box, a bass version of the kalimba or African thumb piano, an Afro-Caribbean form of it that I found in Jamaica 25 years ago. It's a plywood box with a sounding hole and five 6-inch segments of spring steel clamped in a vise in front of the hole. You plug it with your fingers and it can also play hand drums on the front and on the side--on the front it sounds like congas and on the side like bongos."

Other featured instruments of the band are a jug blown by Jonathon Eberhardt, a wash tub (and rope) bass plucked by Lou Leslie and two washboards handled by Bill Riddle and "Washboard Mike" Stradtner. Gary Gregg will be on clarinet, Henry Stenson on vocals and various keyed harmonicas, which he wears in a bandolier, and Dave Robinson on cornet, kazoo and slide whistle.