What were Barry White, Patti LaBelle, Joe Williams and Curtis Mayfield doing on the White House lawn Thursday night?

And why were Jimmy and Rosalynn Carter raising their hands in testimony and singing:

Soon and very soon we're going to see the King, Hallelujah, we're going to see the king .

"This is a celebrated occasion, something to enjoy," said legendary blues singer Joe Williams as he scanned the checkered-cloth picnic tables crowded with 800 black music-makers basking in the hospitality of the White House.

"This is letting America know we're serious about our music, the White House recognition just endorses that," said White, the crooning balladeer of disco, just after he had been besieged by camera-toting admirers.

At this gathering of musicians and administration officials, initiated by the Black Music Association, politics took a back seat to the social event. But the minute Carter appeared on the White House South Lawn, he was surrounded by people congratulating him for his stand on Rhodesia.

Carter, whose credibility has been slipping among blacks, made his entrance to the buffet dinner only a few hours after issuing a strong statement against the lifting of sanctions against Rhodesia.

Randall Robinson, the head of the principal black lobbying group, Trans-Africa, pumped the president's hand and promised, "Black America will be four-score behind you on this issue." The neat timing of the announcement was noted by Del. Walter E. Fauntroy (D-D.C.), who said, "It comes at a propitious time." Fauntroy added that if Carter had announced he was lifting sanctions, "I would not have come. That would have been a serious breach of confidence in the black community."

The mood was festive. People tablehopped even during the performances. The conversations were chatty. A radio announcer, putting his head right up under her wide hatbrim, said happily to LaBelle, "I haven't seen you since that party in South Philly."

Nevertheless, in comparison to the two other largely black music events held at the White House-the birthday party President Nixon gave for Duke Ellington in 1969 and the White House Jazz Festival of last year-Thursday night's event was subdued.

The evening's entertainers, Chuck Berry, Andrae Crouch, Billy Eckstine, Evelyn "Champagne" King and Sara Jordon Powell, were applauded warmly but not wildly.

In his 10-minute segment, Berry converted one of his chestnuts, "Oh Carol," to "Oh Amy," the little girl who was sitting on the grass with a daisy in her hair. But that went largely unnoticed. Only in the final minutes when Crouch, the double Grammy Award-winning progressive gospel singer, delivered "We're Going to See the King" and "Jesus Is the Answer" did the entire audience come to its feet. People were swaying and clapping.

Though serious issues were in the air, the guests, who included record company executives, promoters, disc jockeys and performers, kept mainly to social niceties.

"One of the things missing in the attitudes toward black music is dignity. It's basically white America that calls it race music. This is an endorsement from the highest office in the land, an office that basically represents white America," said Kenneth Gamble, one of the founders of BMA and the successful producer behind the O'Jays, Teddy Pendergrass and Billy Paul.

Though @bma had hoped to attract some of the younger established singers such as Stevie Wonder and Diana Ross, Gamble said he wasn't disappointed they didn't come.

"I talked to a lot of people, a lot of them are working and a lot didn't want to come to the White House," said Gamble. "They are unhappy over government priorities, and I can understand that."

If the musicians didn't gain anything Thursday night but a presidential seal of approval, the administration will most likely gain a couple of points with black voters.

Jerry Hammond, a city council-man from Columbus, Ohio, observed: "Jimmy Carter knows that black folks all over the country like music."

The political aspect was acknowledged by Jack Watson, a White House speical assistant, who said, "Everything the president does has a political aspect. Yet this is also for fun."

And the fun outlasted the food, especially the strawberries, which went early.

After the encores by Crouch, the First Family posed with the gospel singer. And Carter told Crouch's mother: "I know you're proud of him."

Then, as Carter strolled leisurely back to the White House, the Marine Band struck up a song that never made the hit parade: "Stars and Stripes Forever."