LEONIDAS SMITH didn't have to think twice when it came to choosing between his car and his vegetable garden. To save the car from being stolen for the third time, he paved the lower half of his Anacostia back yard, surrounded it with chain link fence, parked the car and locked the gate.

It wasn't long, though, before this man with a green thumb found himself filling trash cans, cinder blocks, planters and battered ice chests with dirt and seeds, producing more than enough fresh summer vegetables to carry him through the season. As usual, there were leftovers to pass out to sons and daughters, fellow church members and the neighbors who have watched his garden grow during the 29 years he has lived in the tidy row house with his wife, Mary.

"At first I was so disgusted," says Smith, smiling when he thinks about giving up the original garden back in l970. "As it turns out, I like it much better." He points out the terraced window boxes for tomatoes and cucumbers built above open cinder blocks overflowing with parsley, scallions and green pepper bushes, among other things. This new system, he says, is far more productive and consumes less space.

Green things are everywhere. Above Smith's car is a dried-out grape arbor from last year's crop. Unusual greens such as rape and mustard grow next to the tires. Tomato plants flourish beside the steps near the chili pepper bush.

But he doesn't stop at vegetables. Smith's front yard is ablaze with flowers of every size, shape, color and hybrid imaginable, all encircling a fat Japanese cherry tree planted in 1939. Along the side of his house are what he calls his geranium trees from which he breaks off shoots to plant in the ground surrounding the narrow cement walkway. His orange and pink dahlias are as big as dinner plates. Mint and spearmint grow next to them. Vines of green beans grow around the rose bushes and cover them as the petals die off, making more room for his favorite garden vegetable.

His secret, he says, is his special fertilizer, a combination he mixes in a large trash can--two pounds of Super Manure, one quart of 5-10-5, 20 gallons of water, 20 scoops of Miracle Grow and lots of love.

"You gotta love 'em like your children to get 'em to grow," he says, adding that plants don't need more than six inches of good soil, fertilizer and plenty of moisture with good drainage. "I try to plant from seed as much as I can," he adds. "I figure if the other guy can do it, so can I." This way he gets more produce for less money and gives the excess away.

"He spends all day in the garden," Mary Smith says. "He sticks a rose in the ground and it grows into a tree. I tell you, I have to watch my old shoes, I'm afraid he might plant them when I'm not looking."

Once the produce is ready, Smith harvests his crops and makes them table-ready. His technique is simple, and he doesn't write his recipes down. His favorite is green beans, boiled with salt pork, salt, pepper, seasoned with cheddar or parmesan cheese. He eats zucchini pickles from the jar year round. BOILED GREEN BEANS WITH TINY NEW POTATOES (6 to 8 servings) 2 pounds green beans 2 pounds tiny new potatoes Water to cover 1/2 pound salt pork, rinsed and cut into slices, or 1 ham hock Small onion, chopped Freshly ground black pepper to taste Grated cheddar or parmesan cheese, to taste

Clean green beans and snap into bite-sized pieces. Wash potatoes. Put in 4-quart saucepan and cover with water. Add salt pork, onion and pepper. Bring to a simmer and cook for 30 minutes just until potatoes are barely done and beans are cooked. Drain and serve sprinkled with cheese. LEONIDAS SMITH'S PICKLED ZUCCHINI 2 pounds tiny zucchini, peeled and quartered Salt 1 teaspoon calcium hydroxide 1 quart water 1 quart white vinegar 2 cups sugr 1/2 box or bottle pickling spice (about 5 tablespoons), tied in cheesecloth

Salt zucchini and set aside for 30 minutes. Squeeze water out with paper towel. Soak in clean water to cover about 2 to 3 hours. Mix calcium hydroxide with 1 quart cold water, add zucchini and let soak overnight. Mix together white vinegar, sugar and pickling spice wrapped in cheesecloth and bring to a boil. Drop zucchini in and return to boil. Remove from heat and pack into hot jars leaving 1/8 inch head space. Seal and process 15 minutes in a boiling water bath.