His suspenders stretched across his expanding middle, Mac Rebennack grinned backstage in New Orleans after wrapping up a triumphant hometown show under his nom de musique, Dr. John. He had rippled quick right-hand triplets over a second-line left-hand boogie-woogie, just like any of his local piano heroes. After years of imitating his betters on the New Orleans rhythm and blues circuit, the 44-year-old Rebennack had finally matured into one of the Crescent City's most accomplished talents.

He speaks with the same coffee-grinder drawl that he sings with as he pontificates on his first and foremost musical inspiration, Professor Longhair:

"I didn't even know who he was when I walked into this joint and saw this guy wearing a tuxedo with a turtleneck shirt and an Army fatigue hat with a watchband around it. Someone brought out a big plate of shrimps and crawfish, and he ate them right there at the piano while the band was playing.

"All the time he was rapping to the people -- walla-walla-this and halla-halla-that. When he was finally done eating, he took off the greasy white gloves and started to play those double note crossovers and over-and-unders and second-line rhythms. He really struck me as someone unique."

Rebennack was just a teen-ager when he first encountered the great pianist in a New Orleans club. But the eager youngster hung around and eventually played with most of the great hometown pianists: Professor Longhair, Fats Domino, Little Richard, Huey (Piano) Smith, James Booker, Allen Toussaint, Art Neville. He soaked up not only their music but their way of life, and tonight he brings his second-line piano pumping, his gris-gris singing and his mumbo-jumbo jive to Club Saba. "Maybe the one thing that makes New Orleans so different is the climate," Rebennack suggests. "It's too hot to hang out inside and watch TV, so people hang out on the front steps and in the bars. Being outside, you just naturally mingle with all the other ethnical groups -- Caribbean, black, Indian, redneck, French and whatnot. All the different musics get mixed up . . .

"Moreover, in the '50s it was such a cutthroat business that musicians had to play everything people wanted to hear or you didn't work. If a club owner wanted to hear hillbilly music, you had to know how to play it. If he wanted calypso or jazz, you had to know that. If I was playing behind a stripper and she wanted Cuban music, I couldn't play R & B."

Because his father distributed records in black neighborhoods, the young Rebennack got to meet all the local R & B players. He learned guitar from Fats Domino's axeman, Walter (Papoose) Nelson, and was touring the South with Frankie Ford and Jimmy Clanton by the time he was 16. Before long he became a studio musician for Ace Records, which scored hits with Huey Smith's "Rockin' Pneumonia and the Boogie Woogie Flu" and "Sea Cruise" by Rebennack's cousin, Frankie Ford.

"Huey inspired me to start writing songs," Rebennack recalls. "He taught me a lot of tricknology -- how to take street chants, jump rope rhymes or slang sayings and make a song out of it with a melody to match. His song, 'Don't You Just Know It,' came from a popular saying . . . .

"At one time, there were several different sets of Huey's 'Piano' Smith & the Clowns traveling around. Back then there weren't all these TV shows, so people didn't know what singers looked like. If the stuff sounded good, they'd go for it. James Booker was Huey for awhile. The musicians didn't care. They didn't see color -- all they cared about was how well you could play."

Out of this environment came an incredibly vital music. Little Richard and Bobby Marchan were stars in evening gowns on New Orleans' competitive female impersonator circuit before they became rock 'n' roll stars. Fats Domino and Ray Charles had to compete on an equal footing with such local stars as Big Maybelle, Willie Jones, Little Jimmy Scott and Smiley Lewis, the "forgotten masters," as Rebennack calls them. Rebennack and Allen Toussaint got their union cards as teen-agers together in 1957. When one of his fingers got shot off in a Florida motel room in 1962, Rebennack switched from guitar to piano.

This golden era of New Orleans music came to an end in 1963, when District Attorney Jim Garrison (of Kennedy conspiracy fame) padlocked most of the nightclubs in a crackdown that put nearly 1,000 musicians out of work.

After moving to Los Angeles and playing sessions for Sonny and Cher, Phil Spector and Frank Zappa, Rebennack conceived the idea of a character named Dr. John, who would dress and sing like a Mardi Gras character. He planned to have Ronnie Barron play the role, but when Barron's manager vetoed it, Rebennack assumed the role himself in 1968.

Dressed up in colored plumes and paint, and with the help of his old friend Allen Toussaint, he scored hits in 1973 with "Right Place, Wrong Time" and "Such a Night." Eventually, though, the high cost of staging his show forced him to abandon the voodoo persona and revert to being a barrelhouse pianist.

Now living in New York, Rebennack writes and performs commercials for Popeye's Chicken in between jazz dates and short road forays. Everything he does, however, still has that New Orleans feel.

"It's part of me, and I'm part of it," he philosophizes. "It's easier to draw on something that's part of your life than from some Fig Newton of your imagination."