IF I HAD space and time enough to raise just one vegetable, and only one, it would have to be the tomato. Ripened naturally by a hot summer sun, this home-grown fruit is a variety unto itself -- juicy, sweet-perfection achievable in just a small amount of earth. No matter how you serve the tomatoes you grow -- sliced fresh from the garden, cooked and frozen for ready use in sauces or soups, even canned -- they add sunny flavor and nutrients.

Unless you were farsighted enough to have started plants months ago indoors, tender tomato seedlings should be purchased now for setting out in the garden. To assure a good crop, choose disease resistant varieties. Plants bearing the initials V, F, N or T after their names have been bred to withstand verticullium wilt, fusarium wilt, nematodes and tobacco wilt respectively. Small Fry (vF), Spring Giant (VF) and Ultra Girl (VFN) are popular determinate or bush varieties. For indeterminate, vining types that will need support choose Supersteak Hybrid (VFN), Better Boy (VFN), Beefmaster (VFN) or Whopper (VFNT). For canning there are plum-shaped Roma (VF) tomatoes on determinate stalks or Campbell 28F for early maturing vines. If you have the space, select several varieties, looking for stocky, dark green, insect-free seedlings. Or consider growing some of the tomato's sun-loving cousins, peppers and eggplants.

All three solanceous fruits will dress up your garden -- stately, staked tomatoes make a classy background for any planting, shiny peppers or purplish eggplants will perk up a perennial bed. They all require rich soil, weed control that won't damage roots (again, mulch is best" and full sun all day long. Plant them deeply -- lower leaves should be just above the ground.

Dig a hole one foot square and deep, working in plenty of rotted manure and compost. Space plants at least 18 inches apart in a row if you plan to stake them, or 4 feet apart if you're going to cage them, or let plants sprawl. For patio gardeners, there are varieties specifically bred for container culture -- Bisty (VF), City Best (VF), Tiny Tim and Patio.

A large bag of peat moss may be the answer for gardening on concrete. Lay bag lengthwise on patio and slit four "X"s, then plant container tomatoes and stakes for an instant garden. Just take care not to overwater since the plastic bag won't drain.

No other home-grown crop seems to invite the gardening gadgetery of the ever popular tomato. There are preplanted seed boxes, steel "towers" to which plants can be staked, folding pens to cage them in, hormone spray to speed fruiting, tomato food (just a 5-10-10 fertilizer available from any garden supply outlet) and the latest rate -- the automator, a square plastic tray that's said to do everything from support the stem to protect against cutworm (as well as warm the soil, mulch and automatically feed and water your plant). It's easy to forget you may have gone to all this trouble of growing your own to save money.

No matter what gadgets you invest in, you will still wait impatiently for the first tomato to ripen. Make the most of perfection when it finally arrives. Tomatoes are the ultimate summer salad, simply sliced and topped with chopped fresh basil. Cooked the briefest of time, they simmer into sweet, fresh sauce or soup. Or preserved carefully, they will provide vitamins A and C year-round.

With tomatoes' high acid content you can put them up easily and safely at home without appreciable vitamin loss. Simply skin by dropping fruit into a pan of just boiled water for 1 minute. Remove any blemishes and press into sterilized jars. Add salt (1/2 teaspoon per pint, 1 full teaspoon per quart) and a sprig of your favorite fresh herb. Remove air bubbles with a spatula and wipe jar necks clean. Seal with commercial canning lids and process in boiling water (35 minutes for pints, 45 minutes for quarts). Tomatoes will make their own juice while you can them.

Cooking tomatoes briefly and freezing has become a popular alternative to canning. The advantage to this method is a cool kitchen and cook. BRONWEN SOUNDER'S FREEZER TOMATO SAUCE

Simmer tomatoes with onion and whatever vegetables or seasonings you choose. Cook until tender. Strain and let sit at room temperature until cool, then refrigerate for 24 hours, being careful not to jar or disturb the settling process. Scoop off liquid (reserving for stock, if you like) and store sauce in plastic containers in the freezer. You don't need to boil down unless you're making catsup. FRESH TOMATO SAUCE (2 or 3 servings) 2 cloves garlic, minced 1 small onion, chopped 2 tablespoons virgin olive oil 4 large ripe tomatoes, peeled, cored and chopped 4 to 6 leaves fresh basil Pepper and salt to taste Spinach noodles Parmesan cheese

Saute garlic and onion in oil until wilted. Add tomatoes and bring to simmer, then add basil, salt and pepper. Cook 5 minutes only. Serve immediately over green spinach noodles and top with freshly grated parmesan. PAT HAMPTON'S GREEN CHILI SALSA (Makes 5 to 6 pints) 1 gallon tomatoes; peeled, cored and chopped 3 to 4 large onions, diced 3 to 6 large hot green chili peppers, cored and diced 3 cloves of garlic, minced 1 tablespoon crushed coriander seeds 1/2 teaspoon each sweet basil and thyme 3 bay leaves, broken up 2 teaspoons salt 2 tablespoons sugar

Mix all ingredients together in a large kettle and cook down until salsa reaches desired consistency (like tomato sauce). Process pints for 45 minutes in hot water bath.