Picture a neighborhood bar with couples dancing a lively two-step to the driving four-four beat of a banjo, string bass and drums. The trumpeter leans forward in his chair and points his horn into a battered tin derby astride a tripod, producing a wailing descant over the gruff trombone and plaintive clarinet. Waitresses deliver rounds of beer to the packed booths. The bar stools are full, too. People come and go, and laughter and conversation are frequently heard over the brassy polyphony of the combo. The music continues all but uninterrupted for three hours. A mournful "Franklin Street Blues" gives way to a relaxed medium-tempo "Bucket's Got a Hole in It." And then the sextet stomps out "Milneberg Joys." The band takes a brief break and the drummer passes the hat.

A New Orleans Kitty Hall of yesteryear? Nope. It's the District's last bastion of traditional jazz, Colonel Brooks Tavern at 901 Monroe St. NE.

For nearly a decade, Tuesday nights at Colonel Brooks have been filled with the sounds of New Orleans-style jazz. Currently the Pontchartrain Causeway New Orleans Jazz Band and the Federal Jazz Commission maintain a schedule of alternate Tuesdays; it was the former that, on a recent evening, created the scene and the sounds above.

Those sounds are hard to come by live these days. To say that the Preservation Hall Jazz Band produces such music is misleading -- although its music is authentic, its emphasis upon solos disqualifies it as a model for the Pontchartrain.

Rather, one must look to California's Magnolia Jazz Band, Japan's New Orleansendcol Rascals or one of several Canadian or British bands for other exemplars of the attack practiced by the Pontchartrain.

"It's not a string-of-solos approach," explains Pontchartrain trumpeter, Dave Robinson. "There's ensemble going all the time; instruments rise to prominence and fade back into the ensemble. Melody is very important and should be there all the time. The trumpeter has to stick to the lead line and do a lot of embellishment but not go off on total improvisation.

"It's a challenge to see how much you can do with the lead line," he says. "The clarinet or trombone may pick up the lead from him and when that happens you drop into a harmony role. But you're still playing. It's pretty much solid ensemble playing. It's really a team effort."

Sound familiar? Probably not, because most traditional-style jazz bands today use as their models the bands that were being recorded in Chicago during the 1920s -- those of expatriate New Orleans greats like King Oliver, Jelly Roll Morton and and Louis Armstrong, or the groups of their young white disciples, including Eddie Condon and Bix Beiderbecke. Those bands emphasized solo statements.

The original New Orleans style, with its dense ensemble and charming heterophony, was not recorded until the "New Orleans revival" of the '40s; before that the record companies had no interest in documenting what was wrongly regarded as only a local folk idiom of minimal sophistication.

Pontchartrain clarinetist Don Rouse points out that the musicians on those records -- Bunk Johnson, Kid Rena, Jim Robinson, George Lewis and others in their fifties and sixties -- were "the home town guys playing the way they normally played."

"I don't think that it's primitive music and I don't think that its practitioners were primitive in any way," Rouse said. "It's a sophisticated act to be able to place notes rhythmically the way those guys did, and certainly there is nothing wrong with their chord changes. I think that the New Orleans style has characteristics that are different and have to be learned. It's a different way of looking at music."

Perhaps William Russell, the idiom's greatest historian, said it best when he dubbed the style "sloppy New Orleans ensemble" and admitted that "almost every sin known to European musical culture is committed." Yet the results, he insists, "are more thrilling than any symphonic group."

Thrilled is exactly what Pontchartrain's leader Dick Stimson was when he was first exposed to the style.

"I saw the George Lewis band when I was in the Navy about '55," recalls the self-taught drummer. "And I sat there for four nights straight."