EVEN THOUGH all-star recording sessions are nothing new in popular music, they seldom result in the kind of commercial and creative success that allows the same musicians to gather again and again in the studio. "The Bluegrass Album, Vol. Four" documents a most welcome exception to the rule -- yet another winning collaboration from six of brightest lights in bluegrass.

Just as the cast has remained the same since Dobroist Jerry Douglas signed on a couple of years ago -- joining guitarist Tony Rice, mandolinist Doyle Lawson, banjo wiz J.D. Crowe, fiddler Bobby Hicks and bassist Todd Phillips -- so has the high level of musicianship and dedication to tradition.

More than half the album is devoted to songs written by Bill Monroe, Lester Flatt or Earl Scruggs, and many of the other tunes reflect their influence.

Most of the selections find Tony Rice singing lead, his voice buttressed by the harmonies of Lawson, Crowe and Douglas on songs like the gospel number "Talk It All Over With Him." Still, it's the band's sparkling, if somewhat less than usually refined, musicianship that makes this album such a worthy sequel.

Gospel harmonies and the music of Monroe and Flatt are also central to the success of the first release by the Nashville Bluegrass Band, "My Native Home." Given Nashville's pop-ish output these days, the band's name may strike some as a contradiction in terms. But begining with the exquisite quartet harmonies found on "Up Above My Head" (and later found on "Blind Bartimus" and "Prodigal Son") there's no mistaking this group's traditional bent.

There's also considerable evidence that banjoist Alan Bryant, guitarist Pat Enright, mandolinist Mike Compton, bassist Mark Hembree and special guest Blaine Sprouse on fiddle can all throw sparks as instrumentalists. Yet it's those harmonies, built around the voices of Enright and O'Bryant, that place this album among the best bluegrass debuts in years.

J.D. CROWE & OTHERS -- "The Bluegrass Album, Vol. Four" (Rounder 0210);

THE NASHVILLE BLUEGRASS BAND -- "My Native Home" (Rounder 0212); J.D. Crowe and the New South, and the Nashville Bluegrass Band appearing Friday at the Birchmere.