It was the first harvest of the season for more than 350 youthful inner-city farmers at the Washington Youth Garden in Twin Oaks Park.

The farmers, aged 5 to 15, celebrated the event in the classical manner this week, with games and good food. Under a late morning sun and the shady trees of 14th and Taylor Streets NW they competed in such contests as the zucchini chin chopper, the carrot balance, the radish bob and a corn-shucking competition. METROPOLITAN LIFE Watching Things Grow

The zucchini chin chopper required both coordination and a zucchini small enough to fit under the tiny chins of children who scurried from one tree post to another and then back to a partner.

Anxious radish bob contestants opened their mouths wide and dipped their faces into small tubs filled with water and dozens of the hard red vegetables. The bob had one unique qualification, said William Hash, director of the Washington Youth Gardens Project. "If you swallow the radishes, you are disqualified."

The festivities marked the 21st harvest of the Washington Youth Gardens, a project run by the D.C. Department of Recreation and the Washington Youth Council with some help from the U.S. Department of Agriculture in the form of seeds and equipment.

The project provides individual plots in three garden centers around the city, the largest being at the National Arboretum. The project's communal gardens at about 75 city recreational centers permit more than 2,000 inner-city residents to try their hand at planting seeds and pulling weeds during summer vacations.

"It is important to encourage community gardening. With food prices in the supermarket skyrocketing, children need to know how to grow their food at home," Hash said.

At the Washington Youth Garden in Twin Oaks Park, there are more than 14 different vegetables including corn, cabbage, carrots, beets and tomatoes, and 12 kinds of flowers and plants ranging from aloe vera to Venus' flytraps. Hash said he expects each gardener to harvest about 50 pounds of vegetables.

During the school year, Hash and another garden manager work in the public schools, teaching elementary and junior high students about the fundamentals of gardening. Children from participating schools volunteer to farm a 5-by-15-foot garden plot. They are given seeds, tools, fertilizer and lots of encouragement. The results are theirs to take home.

"I like growing my own food, especially tomatoes, because I like to pick them when they are green and sit them on my window sill to turn red," said Tirik Davis, 9, of 2126 H St. NE. Farmer Davis was cultivating his garden in the hot sun with a rake several inches taller than he is.

"The hardest thing about gardening is getting rid of the weeds. If they get too big they're really hard to dig up," he said.

"Children are naturally interested in growing things. It's easy and rewarding," Hash said.

Yesterday's event ended with the gardeners eating the vegetables of their labor under a tent near the Twin Oaks greenhouse. Susan Block, wife of Agriculture Secretary John Block, was there to lend her support, and representatives of the Glad Wrap and Bags Co. came to present a check to help fund the project.

"Programs like these become indispensible in the inner city where houses and apartment building replace gardens," said Block. "I encourage more community gardening for children. They need to see the value of their hard work."

Many of the gardeners were impatient to get back to their gardens. "Gardening takes a lot of dedication," said 14-year-old Sean Mack of 1306 Girard Ave. NE.

Mack, who is the youth chairman of the National Arboretum Gardens, has been gardening for five years. To be a good gardener, he said, one has to do four things: plant, cover, water and watch (and eat, of course).

"I gave up a summer job to work on my garden at home because I couldn't leave it unattended," said Mack, whose garden at home has more than 100 kinds of vegetables. Tending it and the garden at the Arboretum always gives him something to do, he said, and is also a source of quiet pride.

"I'm never bored. My gardens give me an opportunity to be able to sit back and say, 'I grew this,' " he said.