Amanda Gowdie's organically grown tomatoes, for sale in front of her house on Arlington Ridge Road, have a captive market. During rush hour, her street is bumper to bumper with automobiles making their slow, painful journey to or from the famous Mixing Bowl.

Gowdie's 3,000 tomato plants nod in the hot, bright September sun. They began coming into harvest only a few weeks ago because of the early summer drought. Gowdie has been picking about 600 pounds a week and selling them all.

There is virtually no resemblance between what she sells and what masquerades as a tomato in the supermarket. Gowdie says that's because of a Department of Agriculture regulation which defines "mature" tomatoes as those containing "jelly." She whips out her pocket knife and proceeds to cut open a tiny, hard, green tomato and points to the "jelly" which has already begun to form. Tomatoes she explains, will ripen after picking only if they have attained a degree of redness while still on the vine. The "red" tomatoes in the supermarket are picked while they are still green and are turned red with ethylene gas. The word "vine-ripened" in the supermarket does not mean ripened on the vine.

That's what makes the difference in taste and texture. In addition, Gowdie's tomatoes are grown without the use of pesticides or chemical fertilizers. "The big secret of everything," Gowdie explains, "is the compost." Her other secret is birdhouses: one for the "big beaked birds which take care of the insects; one for the small beaked birds which take care of the weed seeds."

Gowdie got into the tomato business after she had two heart attacks and had to give up her strawberry plants because they required too much bending. Last year she has 30 tomato plants; this year she increased her plantings 100-fold. The crop comes in two sizes: medium, which sell for 59 cents a pound and large, for 69 cents a pound. "My tomatoes aren't cheaper," she says, "just better." Her hours are 3:30 to 7 p.m., Mon. to Fri: Sat., 10 a.m. to 1 p.m., at 1935 Arlington Ridge Rd, Arlington.

She also has an extensive collection of tomato recipes, which anyone with tomatoes in the backyard would find useful. Here are sample. HEALTH FOOD COCKTAIL

(Serves 2) 2 tomatoes 2 ribs celery Several sprigs parsley 1/2 cucumber, sliced 1/2 zucchini, chopped 1 small onion, cut up

Place all ingredients in blender and blend at high speed until liquefied.

Note: To make tomato soup for four out of the health food cocktail, combine ingredients an blend as directed. Strain and place in saucepan. Add an equal amount of Half 'n Half or skim milk. Season to taste with salt and pepper. Bring almost to boil over medium heat, stirring. Sprinkle with paprika, chopped chives and a dollop of sour cream. AMANDA'S TOMATO AND CORN CASSEROLE

(4 servings) 4 ears corn, kernels cut from the cob 4 large tomatoes, chopped Salt and pepper to taste 1 teaspoon garlic powder 1 teaspoon fresh basil 1 medium onion, chopped 4 tablespoons butter 2 cups soft bread crumbs or cubes 3 tablespoons wheat germ 1/2 cup freshly grated Parmesan cheese

Place corn kernels in bottom of a 9-by-5 inch loaf pan. Top with tomatoes. Sprinkle with salt, pepper, garlic powder, basil and onion. Dot with 2 tablespoons butter. Mix bread crumbs with wheat germ and sprinkle over top. Dot with remaining 2 tablespoons butter and cheese. Bake at 375 degrees for 20 to 25 minutes, until casserole is hot and bubbly.

Note: For variety, add cooked spiral macaroni (rotini), cooked fish or cooked ground beef.