Rock Creek runs through Washington, but what runs through ROCK CREEK is the spirit and energy of songs from the American folk tradition. This vocal trio covers a lot of territory -- sea chanteys, work songs, drinking ditties. But on "Sharon Mountain Harmony" the inspiration is the particularly rich motherlode of gospel song, both black and white traditions. Rock Creek shares the album with Lucy Simpson of Brooklyn, and Mary Alice and Peter Amidon of Vermont. Simpson and Rock Creek alternate leads while providing a constant, thick backing of informal and earthy harmonies with heavenly aspirations. The singing is comfortable, unhurried. No matter which voice leads -- Simpson's ethereal and soft soprano, Bill Destler's gentle tenor or Wally McHenry's persuasive baritone -- it's the richness of the ensemble, the entrancing vocal weaves, that make this album a quiet gem. Another plus is the choice of material. All 16 songs are deeply rooted in prayer meetings, crusty hymnals and songbooks, revival tents, amen corners, rural radio programs; they come from the land and they've been well-used. There's the clipped bluegrass harmony of "Glory Bound," the shape-note urgency of "There Are Angels Hovering Round," the exuberant Baptist release of "Oh, He's Taken My Feet" and "Trouble So Hard," the spiritual grace of "Blessed Quietness" and "Time Has Made a Change in Me," the calming reassurance of "I Will Arise." These are all wonderful songs, beautifully displayed. They reflect intensely personal convictions and a tremendous respect for the grace of unadorned voices singing from the heart. THE DOUBLE DECKER STRING BAND has been a major force in the old-time string-band revival that began in the late '70s. Its second album is tight and percussively compelling: Don't forget, this was major dance music in its day. Once again, the songs come from the authentic Southern tradition, with songs from such folks as Riley Puckett, Uncle Dave Macon and Uncle Dick Hutchinson. The singing is ageless, the playing brightly energetic and the spirit convincingly joyful. ON RECORD, ON STAGE THE ALBUMS ROCK CREEK -- Sharon Mountain Harmony (Folk Legacy FSI-86). DOUBLE DECKER STRING BAND -- Sentimental Songs and Old Time Melodies (Fretless 160). THE CONCERT ROCK CREEK & THE DOUBLE DECKER STRING BAND, Saturday at 8:30 at the Washington Ethical Society Auditorium.