There, among the leafy-topped crates overflowing with collard greens and spinach, was Mrs. Guillory's kindergarten class, winding its way through yesterday's opening of the Washington Open-Air Farmers Market--an assemblage of farmers from far and near selling the fruits of their labors in the Robert F. Kennedy Stadium parking lot.

It's the market's third consecutive year under the Disney World-like Metro tracks, which shade about half of three dozen farmers from the sun and rumble with a deafening din whenever trains pass. For the next six months, nearly all manner of vegetable and fruit, eggs, honey, and iced seafood will be hawked at the market.

This year, organizers expect more than 7,000 people a day to mill through this marketplace born of the search for a way to get reasonably priced fresh produce into low-income neighborhoods where large food retailers were reluctant to tread.

For the first time, the market will be open on Saturdays from 9 a.m. to 3 p.m., in addition to its noon to dusk hours on Tuesdays and Thursdays, explained the market's coordinator, Al Smith.

But yesterday, there were fewer customers on hand than farmers would have liked to see--typical for opening days, the old-timers say. A few blamed a nearby sign that incorrectly informed passersby that the market would open today.

Nonetheless, the farmers challenged boredom by polishing their cucumbers and shaking their baskets of string beans. And they smiled at the wonderment Edith Guillory's kindergarteners held for the veggies a few had seen only in their coloring books, according to their teacher.

"What do you do with these?" asked Guillory's assistant, as she pointed to baskets of plump tomatoes.

"You put them on salads!" shouted the 22 five-year-olds from Charles Young Elementary School at 24th Street and Benning Road, just a minute's walk from the market.

"And how does corn grow? On trees?" she then asked.

Little girls in sun dresses and boys in jeans and summer shirts grew fidgety in the heat. No one answered for a while, then Brian Porter spoke up. He knew. He has been cast as Peter Rabbit in the coming class play and therefore is an expert on such things, Guillory said.

It's all good training for the children, the teacher said, as she prepared to shepherd her class back to school. In her arm nestled a plastic bag bursting with turnps and greens. She couldn't resist.

Makaza Kumanyika planted his massive farmers' hands on his hips and looked down upon the children as if a fairy tale giant, his greeting assuring the little ones that he was indeed friendly.

"All these beautiful boys and girls," he said. "Y'all work hard in school and some of you think about being a farmer when you grow up, because somebody's got to grow the food."

Kumanyika, executive director of Agricultural Teams Inc., a nonprofit farmers assistance agency based in Raleigh, N.C., said he thinks it is important for youngsters to consider farming as a career--particularly black youth.

Black farmers are victims of racial discrimination that nets them lower prices for their produce and limits their opportunities to secure bank loans, he said.

"Without loans, money, a man cannot get his fields into production; without production, he loses his land," Kumanyika said, adding that black farmers in North Carolina are losing their family lands at an alarming rate.

Smith, the market director, said the market organizers made a special effort this year to include black farmers from North Carolina after reading a recently published government report on their difficulties.

Kumanyika said the market is giving some of those poor farmers a hedge against extinction.

"This is an urban-rural economic linkage," he said, describing the benefit of poor black farms finding an outlet for their produce in the inner city.

One day, Kumanyika said, he would like to see black farmers more self-sufficient, owning and operating canneries, exporting food to Africa and the Caribbean.

Yesterday, it was merely Kumanyika's dream. The tractor-trailer truck that brought 28,000 pounds of vegetables grown on a patchwork of poor farms remained pretty full.

"I'm not discouraged," he said, as the last of Mrs. Guillory's kindergarteners disappeared across the baked concrete of the parking lot.