The Kaywood Theatre, located just across the D.C. line in Mount Rainier, seems an appropriate setting for a festival that embraces both urban and country blues musicians. Unfortunately, not enough people know about it.

The disappointing turnout at last night's concert, however, didn't prevent several musicians from making the most of the evening. Street singer Flora Molten opened the concert with her own special benediction, a series of traditional gospel songs punctuated by her resonating slide guitar and the jangle of the tambourine she tapped at her feet.

Guitarist Bowling Green John Cephas and harmonica player Phil Wiggins turned "Amens" into field hollers. Cephas' alternating bass lines, insistent triplets and earthy baritone reflected many roll traditions, while Wiggins poured the heart and soul of country blues through his cupped hands.

Less impressive were "The Incredible Snakes," a local quintet whose songs seldom rose above the ordinary.

By contrast, Chicago pianist Sunnyland Slim and guitarist Hubert Sumlin easily defined the Chicago style despite some audio problems. Slim isn't a commanding instrumentalist but he was more than competent on slow blues and boogie-woogie numbers. Sumlin, one of the most influential of all R&B guitarists, was in especially fine form. He played with relatively little vibrato, preferring instead a tart, rising tone and percussive slides.

Sonny Terry and Brownie McGhee capped the evening with a masterful performance. Terry remains the most inventive and resourceful blues harmonica player alive. Last night, he bent single notes till they cried for mercy and chugged chords so fast he sometimes sounded like a locomotive bent on destruction. The often overlooked McGhee is a more expressive singer, and his guitar playing was full of sly twists and accents. One hopes these musicians will find fewer empty seats at tonight's repeat performance.