* Reed player Mason "Country" Thomas looks back on the '50s and '60s when his bands worked at the Charles Hotel, the Mayfair and countless other clubs in the Washington area. Then Louis Armstrong, Wild Bill Davison and Barney Bigard, among others, would sit in. "There was always something going on, and in the mid-'60s or so it just gave way to the rock thing," he observed from his home in Arlington. Steady work for musicians of his persuasion virtually disappeared a decade ago. But now, in the '80s, things are picking up again. Thomas once again is leading a group that is playing in one location all week, the Jam Restaurant on Georgetown Pike in Great Falls Center, Va. He's got a quartet Mondays through Thursdays and six pieces on Fridays and Saturdays.

What's more, he says, people are coming up to the bandstand and telling him, "Thank God there's a place that has a band that swings."

Thomas contends that the band's approach inspires such commentary. "We're broadminded, not in any particular slot, and might play anything from Duke Ellington's 'Prelude to a Kiss' to an Eddie Condon style 'Blues My Naughty Sweetie Gave to Me.' You get more accomplished musicians when you play a broad range like that."

Trumpeter Dick Mains and drummer Eddie Phyfe have been active nationally since the '40s, trombonist Dave Steinmeyer is leader of the Airmen of Note, pianist Larry Eanet and bassist Van Perry, both long-time fixtures on the local jazz scene, have accompanied many jazz greats passing through the area. For more information call 759-9507.