Under a cloudless blue Delta sky the beanfields are brown and the big blues pickers are grazing over the cotton fields for one day. Blankets and air mattresses are spread out on the rough, hastily cut-over pastureland. The weather is hot. People who arrive in sweaters end up wearing T-shirts stamped "Delta Blues Festival" bought at a concession stand.The mood this Saturday is relaxed, blacks and whites mingling and greeting each other like old friends. If you want to talk to one of the musicians, no one will prevent you from wandering back behind the big flatbed trailer that serves as a stage.

"Hey, man, let me look at your guitar. I hadn't ever seen a nine-string guitar." This from a young man to Big Joe Williams, huge and fat, sweating under the sun after his performance. He's wearing a red T-shirt, stamped "Big Joe, King of the Blues."

"Look at it if you want to," Joe says. "But don't try to take out no patents on it."

On stage Sam Chatmon, who says he is 81 and had a grandmother who lived to be well over 100, shouts out, "Don't mind the cow being pore/Just drink the milk I give you and ask for more/Don't mind the mule being blind/You just sit in the saddle and I jerk on the line. "

Chatmon could sing all day and all night from his repertoire of hundreds of his own songs. He's a crowd pleaser, playing and singing his raunchy, bawdy blues, giving the audience of 5,000 a sly grin and a knowing look. "Cigarette-smokin' woman, throw your butts in here."

Walter "Furry" Lewis of Memphis so feeble at 85 that he has to be carried on and off stage in his chair hollers in the strong voice of a man half his age, "It's a dirty shame - 85 years old, half blind, can't walk. But people, I come way down here to have a nice time."

His long, frail, flexible fingers move over the strings of his guitar. "Blues so bad, baby,/hurt my feet to walk./Got the blues so bad, - it hurts my tongue to talk. "

He is a showman. He plays with his fingers, the back of his hand, his elbow. Sounds like he's playing three guitars. "Arrested me for forgery./Can't even sign my name. "

Out front a woman is dancing along. She calls up at him, "Hey, are you Muddy Waters?"

"No."

'Well, go get him," she says.

'How I'm going to get him? I can't even walk."

The children are eating caramel apples. Beat-up pickup trucks and new Oldsmobiles are parked side by side. Earnest academic types, garden-club ladies, and old-line civil rights activists sit side by side in the grass. The beat picks up. Rural Burnside is playing now, a jump tune, and people are beginning to dance on the stubbily grass, kids, 8, 10 and 12 teenagers, and old folks.

On stage the blues honor roll is being called out: Robert Johnson, Blind Lemon Jefferson, Son House, Howlin' Wolf, Bessie Smith. The black mayors of half a dozen Mississippi towns are brought on stage and introduced. Unita Blackwell, mayor of Mayersville and organizer of Freedom Village, speaks for the mayors. She is majestic. tall, dark-skinned.

"You people are on sacred grounds," she says.

Freedom City, the site of the festival, was organized and built in 1966 at the abandoned Greenville Air Force Base as a result of a sit-in of jobless and evicted black families from the surrounding area. After their ejection from the base, these families, with the help of the National Council of Churches' Delta Ministry, and other philanthropic groups, purchased the 400 acres of farmland and built the village.

Put together by Mississippi Action for Community Education, Inc. (MACE), a Greenville-based community development organization with grants from the Ford Foundation, the National Endowment for the Arts, the Mississippi Arts Commission, and private donors, the festival attracted such famous blues men and Houston Stackhouse, Walter "Furry" Lewis, Piano Red Williams, Chatmon and others less well-known, but equally good, like Othar Turner on the cane fife, Burnside, who drives a tractor all day and sings the blues at night, and Napoleon Strickland, who can make a harmonica sound like a train.

Says Charles Bannerman, president of MACE, "We've already bought the old Masonic Temple in Greenville to house a Blues Institute and Museum. Maybe Museum is the wrong word. We don't want to collect the blues and put it in a bottle. We're not purists or historians. We plan to set up a place where young musicians can come and study with the older men you've been hearing this afternoon. That's the way the blues have always lived and grown and spread.

"This is a beginning, the only blues festival sponsored and put on by blacks. But don't misunderstand me - put on by blacks, but for everybody."

The day began with James "Son" Thomas, singer and guitarist of Leland, Miss. "Come here, Bumble Bee, stop your fuss./You my Bumble Bee/And you know your stuff. "

"Somebody askin' me before I come on the stage about the real old songs, and I know you young people ain't heard this one, because 'Bumble Bee' is at least 50, 60 years old.

"Learned to play on my uncle's guitary," Son Thomas says. "He used to charge me a dollar every time I used it. Playing country dances, when they get to shooting in the house, I'd have to run off and leave my guitar. Go back and get it the next day."

Other old-timers spin their blues yarns, too. Eugene Powell, who grew up in Utica, Miss.: "My mama kept a roadhouse and the blues men used to leave their guitars at the house sometimes. I wasn't supposed to touch them, but when Mama was out at the greens patch, or putting the clothes on the line, I'd sneak and play them. She'd whip me if she caught me. Finally went and ordered me my own from Sears and Roebuck. Cost two dollars and fifty cents."

Thomas, a tall, slender man in his late 40s, famous among Delta blues people for his deep, sweet voice and his bottle-neck guitar technique, sets the themes of love and race with his first three songs.

"God forgive a black man/Almost anything he do. Now, I'm dark-complexioned./Looks like he forgive me, too."

And:

"I would go to Cairo/But the water's too high for me./That girl, she got drownded/Swimmin' long after me."

It's getting dark now. Little Marcellus is on stage, 15 years old, already a pro. He will be followed by Piano Red Williams, the old Howlin' Wolf band, the Oliver Davis Band, Van Hunt of Memphis, queen of the Blues, accompanied on the piano by Mose Vincent.

Up on the trailer, Big Jack Johnson from Leland is shouting out, "Blues like the boll weevil. Spread all over the world." It's dark. The bands are playing. The people are dancing. Nobody wants to go home.

Ellen Douglas is a novelist from Greenville, Miss., whose most recent book is "Apostles of Light." Her eldest son is a blues singer and composer.