The austere beauty that emerges from the polyphonic chaos of a New Orleans band in the heat of ensemble remains one of the more arcane mysteries of jazz. A highly appreciative audience, many in formal attire, was witness to the act if not made privy to the secret last night at the Wolf Trap Preservation Hall Jazz Band Gala in Constitution Hall.

The components of the musical enigma were the plaintive and driving trumpet of Percy Humphrey, the soaring clarinet of his elder brother Willie Humphrey and the hoarse moan of Frank Demond's tailgate-style trombone. The honky-tonk piano of Sing Miller and the tuneful strumming of Narvin Kimball's banjo partook of both melody and rhythm. Allan Jaffe's basement boom sousaphone and the varietal effects of Frank Parker's drum kit kept the beat.

Such classics of the genre as "Ice Cream" and "His Eye Is on the Sparrow" provided solo spots. Both Humphreys, Miller and Kimball contributed period vocals. At evening's end the stage of the staid hall was invaded by a parasol-led parade of dancers to "The Saints Go Marching In."

The Marine Corps Marching Band, resplendent in red and white, opened the evening with rousing deliveries of the National Anthem and several marches.