New Grass Revival: adventurous band that won't be pigeonholed. MUSICAL CROSSOVERS

New Grass Revival is a taut, crisp band that uses traditional bluegrass instruments to play contemporary music, drawing on a multitude of musical styles. Rock, bluegrass, country, blues, jazz, gospel, and reggae all scampered across the frets at their recent performance at the Berklee Performance Center here. It was an evening of proud individuality: New Grass was bookended by Steve Warriner and Nanci Griffith, who also refuse to be pigeonholed by easily marketable genres. Mr. Warriner, who has a pure country voice similar to George Strait's, worked in some Windham Hill acoustic strains, as well as a thunkin' ``Freight Train.'' Headliner Griffith calls her style ``folkabilly'' and combines complex poetry with a down-home country sweetness.

The three acts are part of ``the new traditionalists,'' performers who cross boundaries and are even getting big-label record contracts.

The promoter of the evening, FolkTree's Harry Lipson, introduced New Grass as ``the world's greatest band.'' He's not alone in thinking they're pretty remarkable.

The band, which has been around since 1971 and with these four players since 1981, has tremendous energy, lightning-fast playing, and a seamless tapestry of sound that comes from years of working together.

``They're equally good as individual members as they are as a unit,'' says Lee Michael Demsey, of WAMU in Washington, D.C., a heavily bluegrass station. ``They know every nuance of what the others are doing; they're like clockwork.''

They're also known as ``musicians' musicians.'' At Berklee, Pat Flynn played acoustic guitar as hard as if it were electric. Sam Bush, the only member of the original band, is acknowledged as one of the best mandolin players and best fiddlers around. He played so fast it sounded like a machine gun. Bass player John Cowan brought a supple, soaring voice to anchor the vocals. Bela Fleck is said to be the most influential banjo player to come along in the last decade.

The group, nominated for a Grammy earlier this year, has released 11 albums and has just brought out its second on a major label, Capitol/EMI America. It's played folk, jazz, and bluegrass festivals all over the United States, and in Africa, India, Nepal, and Europe. And it has they've opened for acts as diverse as Leon Russell and Loretta Lynn. All four members have hefty independent careers as well.

``Metric Lips,'' written by Mr. Fleck, was an instrumental filled with time changes and intricate solos. Knowledgeable listeners could pick out the layers of jazz and rock threaded through the song simultaneously. While the group's forte seemed to be hard-driving numbers, the real scorcher was Mr. Cowan's version of the Staple Singers' ``You Don't Knock,'' sung in the funky falsetto of Little Richard. The most bluegrassy was ``Hold to a Dream,'' the title of their current album.

The group had the relaxed friskiness that comes with doing a job well. One song started out sounding like ``La Bamba,'' but turned into ``Twist and Shout'' `a la Los Lobos, with a little Earl Scruggs thrown in.

During a backstage interview, Flynn and Fleck talked about the general opening up of music to new styles. ``There are great opportunities. Look at the Police doing reggae; Graceland was a major inspiration,'' says Flynn. ``Bela's been delving into Irish music in the last couple of years. If we hear a sound that we really like, we try to find some way to incorporate some part of it in our music. I think what we're trying to do is make music that's across the board.''