"Frog" Joseph pugged up his cheeks until they were as big as crabapples, put his trombone to his lips and tootled out the first notes of "Way Down Yonder in New Orleans."

As if on cue, the lights went down in the art deco ballroom of the river steamboat S.S. President where about 1,300 jazz buffs had gathered for an evening of jazz, ragtime and spirituals Sunday as they cruised up and down the Mississipi River. This was the second of seven concerts of the New Orleans Jazz and Hertiage Festival, which continues through this weekend.

The star of the night was 34-year-old ragtime pianist-composer Eubie Blake, who sat placidly at a "table through the first act - Louis Cottrell and the Heritage Hall Jazz Band - with his spidery fingers wrapped inside a white crocheted shawl. "It's my wife's doing, to keep 'em warm and limber," he said. "She coddles me."

At first, Cottrell's band played through a series of genteel pieces that no one recognized. "Can you figure out the name of this music?" said Dick Allen, curator of Tulane University's jazz archive. "Nobody can, but it's good."

The air conditioning was going full throttle, but the ballroom kept heating up as people crowded onto the floor to watch and clap time. Allen loosened his tie, which showed and army of crawfish marching toward hiis throat, beat time and smiled.

The tempo changed during "I Want To Be Happy." Joseph used the rubber part of a plumber's friend to achieve some brassy tones, drummer Freddy Kolhlman started playing faster and faster. And trumpeter Teddy Riley was soaring. In the back of the ballroom, Ellyna Tatum stood up and began to bump and grind in time.

"Oh, play that jazz" the musicians hollered in unison as a red spotlight was flashed on them, heating up the atmosphere even more for a rendition of "The Second Line."

In Jazz jargon, the second line is the retinue that struts behind a jazz band, as it winds through the streets, using parasols to keep time the way a drum major would use his baton. As the song steady one-two, one-two tempo increased to fever pitch, a contingent of spectators stood up, opened wildly colored parasols and started to promenade, dragging others to their feet as they passed their tables.

Leading the way was a bouncing navy blue umbrella with "I Love New Orleans" written all over it, topped off with a paper rose. Following it was a yellow model with green trim, wielded by French-Quarter artist Ana Lane; then came one in blue with a fake dove perched on top, a red one, another in four shades of blue, and one in pink gitter and black feathers.

Husbands left wives, bartenders deserted their stations, and waiters stopped waiting on tables long enough to step in time to the beat. It was enough to make them forget that it was raining outside and that the water was leaking through the roof and onto the stage, where concert staffers quickly collected the water in plastic beer pitchers.

Sitting at a front table, Rosalind Kohlman, the drummer's wife, could sit still no longer. Spreading her arms like a funky scarecrow, she fell into line and stepped off the beat.

"This is one of the few times I get to see my husband," said Kohlman, who has a five-day-a-week job as a Navy commissary cashier. "He got in today from Cleveland at 12:30 and had to play for a wedding at 1. That lasted til 3:30 p.m. and he had to come for this, and he's leaving for Hawaii May 1.

"I'm a widow half the time, but when I hear something like this, it's worth it. It's in your blood."

The music roared to a finale, and Blake was led on stage acknowledging the standing ovation with his hands clenched above his bald head in the prizefighter's salute.

"I know you gotta have some nerve to follow this band," he said, "but I got some nerve."

Blake always plays from memory, but he keeps a list of selections in his coat pocket to give him an idea of how long his set should be. "I don't trust my memory," he said to loud laughter as he fished a wrinkled piece of paper from the breast pocket of his coat, read it and launched into one of his rags: "Troublesome Ivories."

His elegant fingers scampered up and down the keys, easily threading through the syncopations as his feet worked like pistons to keep time. Occasionally, the punctuated his playing with series of "da-da-da-das" and "ya-pa-pa-pas" during particularly favorite runs, and after a few minutes, he disregarded the little program sheet and started playing what he felt like playing.

He didn't limit his act to the keyboard. Before launching into "The Charleston," he announced he was going to show of the dance, as members of the audience held their collective breath, hoping he wouldn't fail down. He struggled to his feet, shuffled off a few steps and stopped, saying, "I would go a little futher but there's no use running it into the ground."

The program was primarily ragtime, but Blake took detours to play his tender "Memories of You," a medley of "Rhapsody in Blue" and "The Man I Love," and "I Got This Old-Fashioned Love in My Heart."

He also took time to honor his wife and manager, Marlon, who has carefully handled his career since it took an amazing rebound during the 6-year-old ragtime revival. "She takes care of my business," he cackled and leered, "the little business that I have."

He then began the "Charleston Rag," which he composed in 1899 - long before most of his spectators were born. He raced through the syncopated runs, lingered tenderly over the slower, more intricate parts and roared to a conclusion shouting, "and that's it" as he hit the final chord.

To bring the steamboat back home, the Wallace Devenport All Stars came on stage. After fast renditions of "I Can't Give You Anything But Love" and "If I had My Life to Live Over," the band launched into "Tin Roof Blues," a steamy selection whose mood matched the high humidity outside. The rain had stopped, but clouds hung over the boat, making the river look pudding-murky and almost obscuring the skyline that was getting steadily closer, as the boat approached the dock.

While most of the audience went wild over Ernest Elliott's drum sole in "Ting-a-Ling," veteran musican Paul, Barnes sat quietly at a table.

"I like it pretty good in the audience," said Barness, a member of the Preservation Hall Jazz Band, who wore clarinet and saxophone tie clips and a third clip showing a line of music, "Sitting here, I can tell what they're doing right, and what they're doing wrong. They're doing most things right, but some things, they're playing too fast. I know, I played with Jelly Roll Norton. "King" Oliver and Louis Armstrong - I played with all of them."

The All Stars were joined by the Zion Harmonizers, a male quintet inblue-and-white houndstooth-check blazers and blue pants, who belted out spirituals. They brought Aline White onto the stage to lead singalongs of "Just a Closer Walk With Thee," a standard at New Orleans jazz funerals, and "When the Saints Go Marching In."

As the music peaked, Pat Jaynes of Stillwater, Okla., tapped time on her table top and said, "It had better be reported that jazz lives."

With that, she joined the "second line" that danced the President into the port to the tune of "Down by the Riverside."