It was raining and it was late. So late that Saturday, July 5, 1958, had given way to Sunday when announcer Willis Conover told the capacity crowd at the Newport Jazz Festival: "Ladies and gentlemen, it is Sunday and time for the world's greatest gospel singer, Miss Mahalia Jackson."

For 46 minutes, 50 years ago today, the force of nature known as the Rev. Martin Luther King Jr.'s favorite singer briefly washed aside racial divisions in white and black America.

On that grassy Rhode Island field, a mostly white, well-dressed, well-to-do crowd of jazz listeners sat on wooden folding chairs and clapped, danced, sang and prayed shoulder to shoulder with black fans.

"Saturday had been a long day. But everyone stayed to hear Mahalia," recalls Columbia Records jazz producer George Avakian, 89, who was overseeing two Ampex reel-to-reel tape machines recording the concert.

"I had no idea we were shooting history," says "Jazz on a Summer's Day" filmmaker Bert Stern, 78.

Fellow New Orleans native Andrew Young, 76, recalls, "When Mahalia sang, she could dredge up all the power and suffering of 200 years of slavery and transform an audience of any color."

In "Movin' on Up," her 1966 memoir, Jackson pointedly observed: "When you move back and forth between the white and colored worlds every day, the stupidity and cruelty of some white people hits you so hard you don't know whether to explode or pray for someone who has such hatred in his soul."

Jackson's passport into those worlds, however, made her a unique singing soldier in the civil rights movement.

Five summers after Newport, in 1963, Mahalia Jackson would appear with King at the Lincoln Memorial. At the March on Washington, Jackson would galvanize a wandering crowd of 250,000 black and white Americans.

Then, for her encore, the singer quite possibly ended up inspiring one of the world's greatest speeches.

Queen of gospel

In 1958, booking the queen of gospel —- a woman who steadfastly refused to perform secular music —- at the 4-year-old Newport Jazz Festival was unconventional.

"[Jazz promoter] George Wein was trying to widen the appeal of the festival," said Avakian, who helped get her signed to Columbia in 1954.

Due to her rising popularity, Jackson was given the final slot on a Saturday night program that even included Chuck Berry rocketing through "Sweet Little Sixteen," to the horror of jazz purists in the audience.

"Booking Chuck Berry was considered scandalous!" Avakian said. "But booking Mahalia was inspired. She was not someone you could just go out and see anytime like Count Basie. Besides Newport, I don't know of any other festivals she ever played."

And with first-time filmmaker Bert Stern shooting and Columbia Records rolling tape, it would become one of the best documented performances of Jackson's four-decade career.

Stern and Aram Avakian's 1959 film of the festival is considered by the Library of Congress to be the finest jazz documentary ever filmed. A 50th anniversary presentation of the film screened at Lincoln Center in New York on Friday night. Jackson's live recording, "Newport 1958," remains among the most popular in her catalog.

From the moment a beaming Jackson, resplendent in a white gown, takes to the microphone and her burnished contralto amplifies the opening verse of "An Evening Prayer," the audience is instantly enamored.

"On the album, you can practically hear the crowd sitting up in their seats," says Nedra Olds-Neal, an independent producer who oversees Jackson's Sony's Legacy album reissues. "When Mahalia opened her mouth, there was no way for your attention to be divided."

Ironically, "Newport 1958" also helped the singer repair ties with her core audience in black churches.

By the late '50s, Jackson was experiencing unprecedented success via her crossover recordings for Columbia.

For some hard-core gospel fans, the pop instincts of Columbia producer Mitch Miller (famous for saddling singer Rosemary Clooney with the cloying "Come on a My House" and his own series of saccharine "Sing Along With Mitch" recordings) resulted in some of Jackson's oldest fans labeling her a sellout.

"The folks who grew up seeing her didn't like the Mickey Mouse arrangements," said Bil Carpenter, author of "Uncloudy Days: The Gospel Music Encyclopedia."

But at Newport, Jackson arrived with just a bassist, organist and her longtime pianist Mildred Falls.

"It was stripped down to Sunday prayer meeting," reflects Olds-Neal.

For Andrew Young, Atlanta's future mayor, she was Miss Mahalia, a household name he grew up listening to in New Orleans. "She was able to cross over at places like Newport because she performed songs straight out of the Baptist and Methodist hymn books. These were songs that were also known in the white churches. It connected her to everyone."

Since 1955, when the Rev. Ralph David Abernathy and King first asked her to perform during the Montgomery bus boycott, she stayed busy behind the scenes raising money for King's causes.

"She was a powerful voice in the civil rights movement not only because of her singing voice, but because of the massive reach she had across the races," says Rep. John Lewis (D-Ga.), 68. "She brought inspiration and optimism to us all. She created, as Bobby Kennedy used to say, 'ripples of hope.' "

For many, the pinnacle of Jackson's work with King occurred on the afternoon of Aug. 28, 1963, at the March on Washington. CBS interrupted its soap operas to televise Jackson's performances of "I've Been 'Buked" and "How I Got Over."

Young and Lewis recall how her spirited singing, after a long afternoon of speeches, snapped 250,000 sun-drenched backers to attention.

"She managed to whip up all those tired people and get them ready for Martin," Young says.

And according to some in the crowd, Jackson's contributions didn't end there.

Jackson was seated to the side of King during his speech. As he neared the end, he departed from his prepared text and began preaching.

That's when those close to the pair reportedly heard her urging King, "Tell them about the dream, Martin. Tell 'em about the dream!"

Relates Lewis: "Mahalia was up there serving as Dr. King's own amen corner."

Less than five years later, Jackson would sing at King's funeral in Atlanta. In the liner notes for her tribute album, "Mahalia Jackson Sings the Best-Loved Hymns of Dr. Martin Luther King, Jr.," released 40 years ago this summer, the singer said of her friend: "I never thought of Dr. King as ordinary. There hasn't been a man like that since Jesus."

Bert Stern recalls a similarly religious revelation about Jackson that rainy morning at Newport. As Jackson launched into a rousing rendition of "Didn't It Rain?" the skies opened.

" 'Didn't it rain, children, didn't it rain?' " Stern recalls, reciting the lyric. "Yes, it did. Somehow, everything stayed dry."

Uncertain whether to proceed with her encores, Jackson surveys the crowd, saying: "You make me feel like I'm a star. I don't know if you want to stay in the rain, but I'm just getting warmed up."

The crowd cheers its approval. Jackson calms the crowd enough to begin "The Lord's Prayer."

And filmmaker Stern was faced with a final dilemma: Abide by festival organizers' request to cut off the cameras during the solemn selection or capture it for "Jazz on a Summer's Day's" finale.

If you listen closely, on both the live recording and on the documentary's soundtrack, you can hear the hum of movie cameras.

Says Stern, sheepishly: "It was just too special not to capture. Fifty years later, it's a chance I'm glad we took. I can't think of a more perfect way to end the film."