AFTER THE SUCCESS of last year's "Plain Dirt Fashion," which ushered Colorado's eclectic Nitty Gritty Dirt Band into the country mainstream, the quintet has reunited with producers Marshall Morgan and Paul Worley on "Partners, Brothers and Friends."

Once again, Morgan, the engineer who crafted the patented Ricky Skaggs sound, takes the band's bluegrass roots and original songs and shapes them into commercial country at its most appealing.

Though the material isn't as strong on this return trip, the punchy drums and bass give the music a catchy presence without overwhelming the refreshing bluegrass picking and vocals from the band and such guests as Mark O'Connor, Sam Bush and Jerry Douglas. Three fine songs pay fond tribute to pastoral homelands: Wendy Waldman's lushly harmonic "Home Again in My Heart," Mike Cross' "Poor Farmer Narrative, Leon McDuff" and Jimmy Ibbotson's fiddle-enlivened "Telluride."

Bluegrass takes quite a different direction on a self-titled collaboration by John Hartford (the banjo minstrel who wrote "Gentle on My Mind"), Vassar Clements (the fiddle virtuoso who has played with everyone from Bill Monroe to the Nitty Gritty Dirt Band and The Grateful Dead) and Dave Holland (the great jazz bassist who has played with Miles Davis, Chick Corea and Sam Rivers).

Unlike most bluegrass-jazz fusions, this project doesn't rely on swing or speed but instead on the harmonic intelligence of the musicians. Hartford's guitar and Clements' fiddle search patiently for unexpected, counterpointed harmonies above Holland's restless bass line on "Til Something Better Comes Along." Hartford's banjo carefully plucks out contrasting lines to Clements' lonesome fiddle on Holland's majestically pastoral "Memories Of Home." Hartford sings with understated wit on three of the 10 numbers.

THE NITTY GRITTY DIRT BAND -- "Partners, Brothers and Friends" (Warner Bros. 9 25304-1); appearing at Wild World Sunday at 6 and 8.

VASSAR CLEMENTS, JOHN HARTFORD & DAVE HOLLAND -- "Vassar Clements-John Hartford-Dave Holland" (Rounder, 0207); The Vassar Clements Bluegrass Band plays the Birchmere at 9 on Friday.