MANDOLIN virtuoso David Grisman calls his distinctive hybrid of bluegrass jazz "dawg music." On his latest album, Grisman breaks down that hybrid into its two original sources. The single record has two different titles and two different front covers. One side is "Dawg Grass" (Warner Bros. 23804-1), with the band's mutt mascot, Buttons, in a cowboy hat by a haystack; the other side is "Dawg Jazz," with Buttons wearing shades in a smoky nightclub. Despite the packaging concept, the hybrid nature of "dawg music" remains, with a rural twang slipping into the jazz side, and sophisticated chord variations slipping into the bluegrass side.

The concept seems merely an excuse to invite some top jazz and bluegrass string players to engage in stimulating musical conversation with the four virtuosos of the David Grisman Quartet. "Dawg Jazz" begins with the quartet anchoring a 15-piece big band of such mainstream West Coast jazz greats as Pete Christlieb, Conte Candoli and Tommy Newsome. Grisman's prickly mandolin notes stand out all the more sharply against the rounded horn notes of the swing arrangement.

On his own "Steppin' With Stephane" and Duke Ellington's "In a Sentimental Mood," Grisman and bassist Rob Wasserman join legendary violinist Stephane Grappelli and guitarist Martin Taylor. Grappelli's mix of gypsy folk music and jazz was a big inspiration for "dawg music," and the two old friends follow each other's lyrically improvised lines with telepathic empathy. Fiddler Darol Anger and guitarist Mike Marshall show a similar empathy on the brisk, dextrous run of Anger's "Fumblebee."

On "Dawg Grass," Grisman pays tribute to another inspiration, mandolinist Bill Monroe, the "Father of Bluegrass." "Happy Birthday, Bill Monroe" radiates an unmistakable affection as Grisman ticks sharply against the sweeping twin fiddle lines of Anger and Marshall. When Grisman pays tribute to Flatt & Scruggs with "Dawggy Mountain Breakdown," Earl Scruggs himself helps out on banjo. Grisman's variation on "Foggy Mountain Breakdown" captures the original flavor and high speed and then converts it with odd jazz harmonies.

Guitarist Tony Rice, an alumnus of Grisman's band, plays on four of the six "Dawg Grass" cuts and adds the perfect melancholy tone to the traditional gospel lament "Wayfaring Stranger." Dobro specialist Jerry "Flux" Douglas plays on five of the "Dawg Grass" tracks and adds the necessary bluesy whine to "Swamp Dawg." But "Dawg Grass/Dawg Jazz" is much more than just a collection of skillful solos. Grisman writes tunes with a grabby melody and a dramatic structure and then creates a true ensemble rapport in the performances. Not only does he define the technical attributes of jazz and bluegrass, but he draws on the restless searching of jazz and the emotional concessions of bluegrass.

Grisman's strong presence and his all-star guests often distract attention from the unusually high caliber of his sidemen, all of whom could be band leaders in their own right.

Darol Anger and Mike Marshall have stepped out on their own to produce a duet album, "The Duo" (Rounder 0168). Both are multi-instrumentalists; Anger plays violin, mandolin and cello on the album; Marshall plays guitar, violin, mandolin and mandocello. They tackle an ambitious repertoire that includes a Bach piece for solo violin (played by Marshall on solo mandolin), Charlie Parker's "Donna Lee" (played recklessly with car crash sound effects to match), Chick Corea's "Children's Song," the bluegrass standard "Golden Slippers," plus six originals.

Anger and Marshall bring all the assets of Grisman's "dawg music" to their project, but their music takes place as a dialogue rather than as a symposium. This makes each voice more distinct and thus easier to get to know. Marshall's playing is more aggressive as he pushes the tempo and stretches the melody. Anger is more patient, as his playing flows with the momentum until it finds an opening and spins off into a new discovery. Together they avoid the technical formula of so many acoustic pickers and engage in a give-and-take that is as refreshing as it is unpredictable.

The fourth member of the Grisman Quartet, acoustic bassist Rob Wasserman, plays on two tracks of "The Duo" and has released his own album of unaccompanied bass pieces, "Solo" (Rounder 0179), with Grisman producing. Unaccompanied bass solos may seem unappetizing to most people, but Wasserman has a most unusual approach to the instrument. He plays in the bass' higher octave and plucks sharply defined notes, not unlike a mandolinist. Underneath this melodic top he thumbs a simultaneous bottom line, thus giving his solos two voices. He also gets a high, fluid bowed sound that almost has a whistling effect. Playing his own attractive melodies with these and other techniques, Wasserman brings a surprising sense of invention to this most taken-for-granted of instruments.

Wasserman has also released a set of six one-hour cassette tapes that provide instruction in playing the upright bass. The step-by-step course goes from the basics to blues and bluegrass licks to the distinctive style Wasserman developed for "dawg music." Grisman and Marshall accompany him on the last three tapes. The whole set with an illustrated book is available for $55 from Homespun Tapes Ltd., Box 694, Woodstock, N.Y. 12498.