Ten years ago, JIMMY ARNOLD was heralded as a prodigious new talent. After years of struggling with deep-rooted personal problems, he's come back, older, wiser and just as prodigious. "Rainbow Ride" focuses on Arnold's banjo in hot counterpoint to Mike Auldridge's exquisite Dobro. But thanks to overdubbing, Arnold also stands in on fiddle, and harmonic, lead and rhythm guitar, competing with himself on the breaks. At least he's good enough to keep up with himself. The totally instrumental album is heavy on rags, swing and bluegrass: There's a sparkling "Entertainer/Maple Leaf Rag" combo, a sprightly "Hub's Rag" (for the publisher of Banjo Newsletter), the strange twin-banjo "Medusa" and a stunning rendition of "Swanee River" that starts out as a plectrum banjo arrangement, slides into ragtime and ends up as delirious bluegrass. Arnold is simply astounding: His approach is always aggressive, downright fiery, yet tremendously inventive and flawlessly executed. He also throws in little surprises -- rhythmic tricks, song quotes and such -- without seeming to show off. Arnold is back in style. BILL HARRELL got his start in bluegrass more than 30 years ago while an undergraduate at the University of Maryland. A veteran of Washington television in the '50s, he's perhaps best known for his 13-year partnership with Don Reno, which ended in 1976. A fine guitarist, Harrell is also appreciated for his easy, relaxed singing style and the fine musicians in his backing band, the Virginians. "Blue Ridge Mountain Boy" is a mix of originals and adaptations that showcase fiddler Carl Nelson -- one of the very best in the business, he incorporates elements of swing and country -- and the group's solidly traditional approach. There are a few glitches -- some draggy tempos and a slow-waltz rendition of "Nearer My God to Thee" that's meant to sound church primitive but doesn't -- but the album is mostly smooth and sure. Among the highlights: nice grassy adaptations of Fred Rose's "Blue Eyes Cryin' in the Rain" and Dolly Parton's "Put It Off Until Tomorrow," a sparkling pair of instrumentals that go round the horn in fine style. Best of all are the turn-of-the-century waltz, "I Love You the Best of All," and "Hushed and Still," a wistful celebration of traditional rural values graced by a lovely melody. ON RECORD, ON STAGE THE ALBUMS BILL HARRELL & THE VIRGINIANS -- Blue Ridge Mountain Boy (Rebel LBG-8106). JIMMY ARNOLD -- Rainbow Ride (Rebel REB- 1063). THE SHOWS JIMMY ARNOLD and several other bands, Sunday afternoon at 3 at the Birchmere. BILL HARRELL and other bands, Sunday night at 7 at the Birchmere. Both shows are fundraisers for WAMU.