Sara Clapp can use up an entire head of garlic when she cooks dinner for two. Not just one of those puny heads that come two to a box, but the large head which can be purchased separately in many ethnic grocery stores.

Garlic, along with enormous quantities of fresh lemons, dired mint and oregano, are the staple seasonings of Clapp Argentine-influenced Greek cooking that has been adapted to American ingredients. And her Yankee-thin, New England-born husband, Steve, thrives on eating quantities of it, nevery gaining an ounce because he runs 6 to to 8 miles a day, 20 on Saturdays and Sundays. Since she doesn't run, she just eats less.

Not that the food is really fattening. On the contrary it's just that it tastes so good, one is tempted to eat a great deal of it. Actually what the Clapps eat and feed their two small children is proof that delicious food doesn't have to be sweet or contain great quantities of fat.

Clapp, who was born in Argentine to Greek Sephardic Jewish immigrants, says her mother never gave her a sweet for a snack when she was a child, though there were always desserts for special occasions. Instead she would have a carrot stick, a piece of lemon with salt (a treat she describes as "delicious"), possibly a round hard cracker with oliver oil and garlic. Her mother, she said, somehow "knew about what was good for children."

That kind of background, coupled with her interest in her husband's work as editor of the Community Nurition Institute Weekly Report, has made her very conscious of the importance of a good diet. Community Nutrition Institute is a consumer interest organization that acts as a watchdog over federal activities involving nutrition and health, particularly the Department of Agriculture.

"Cupcake and stuff like that, it's empty calories," Clapp said. "I think it's bad for your teeth. It make you fat. We don't have soft drinks either. I give the children orange juice or V8 or apple juice or that purple drink. What do you call it? Grape juice?

"We went to visit some people last week and the child was eating a package of little donuts for lunch. Isn't that an awful thing to give children?" Clapp said. "When we go on a pinic I make a little package of a piece of chicken and some vegetables for the children." Meats processed with sodium nitrite are on the forbidden list, too.

The children, Emilia, 7, and Melissa, 2, thrive on that kind of food though the older one has some problems with what is served to her for school lunch. "Emilia doesn't like sweets or meats with all the gravy at school so when they serve that she takes her lunch," her mother explained.

The younger child is fed the kind of lunches toddlers used to get about 30 or 40 years ago: calves' liver with mixed vegetables and dried or fresh fruit with lowfat milk or juice; meatball (leftover from the previous night's dinner) with vegetables and sliced tomatoes on the side.

Weekday breakfast are fresh fruit or juice, hard-cooked eggs for the children, cold cereals but not the sugar-encrusted varieties, toast with jelly and Milk. Weekend breakfasts are a little more elaborate with Spanish or cheese souffle a frequent feature. Often the family drinks the typical Argentine beverage for breakfast, yerba mate , a bitter dried herb which is brewed like tea.

It's at dinner that the garlic, lemons and spices come into their own. But curiously, even when Clapp has meatballs with garlic on top of the stove and is cooking chicken with garlic and a spinach tortilla with more garlic in the oven, her Southwest townhouse is not permeated with its pungent odor. Nor does the food taste only of garlic. Actually lemon is the most pervasive flavor, but not so much so that it masks the expert blending of herbs.

Clapp learned Greek cooking from her mother, who "never used a recipe in her life," and Italian cooking by watching the mother of a friend of hers when she was a little girl. She said she loved to cook and helped her school earn money at its annual fair by making and selling food.

Today she likes to cook in large quantities so that there is enough for leftovers, especially for Sundays. This week, however, her husband is on his special pre-Boston Marathon diet.

Steve Clapp runs in the Boston and Baltimore marathons each year and for a week before each race his diet is completely changed. For the first three days he eats high protein foods; no sugar and no starches. For the three days immediately before the race he goes on a carbohydrate-loading diet, consuming mostly starches such as rice, pasta, potatoes, bread and various grains. This is an accepted form of training for the grueling 26-mile races.

The main dish recipes that follow, however, are normal family dinners which the children eat at 6:30 and Clapp and her husband eat later. They are served to company. If the idea of an entire head of garlic in a dish for 4 or 6 people is overwhelming, start with less and gradually work up to what please your palate. CHICKEN WITH LEMON

(4 to 6 serving) 2 whole chicken breasts, halved and 3 chicken legs 3 lemons 1/2 head of garlic, peeled and finely chopped 1 bunch spring onions, thinly sliced 1 tablespoon each oregano, thyme, rosemary and marjoram 1 cup white wine, approximately Salt and pepper to taste 4 to 6 potatoes, peeled and halved. 1 green pepper, chopped 1/4 pound margarine

The day before serving, combine the lemon juice, cut up lemon rind, garlic, onions, spices and wine and marinate the chicken in a bowl in the mixture, turning occasionally. To bake, pour half the marinade into a bowl and reserve. Place chicken in shallow pan in single layer with potatoes and green pepper. Top each chicken piece and potato with pat of butter. Bake, uncovered, at $50 degree for about 1 1/2 hours, until chicken and potatoes are done. Baste frequently with reserved lemon-wine mixture. If necessary add more lemon and wine to keep chicken moist. Serve with rice. MEAT BALLS WITH LEMON AND GARLIC

(8 servings) 4 slices whole wheat bread 2 pounds ground beef 2 tablespoons parsley 1 head garlic, peeled and finely chopped 2 tablespoons dried mint leaves or 6 tablespoons finely chopped fresh mint 1 teaspoon paprika Salt and pepper to taste 5 or 6 eggs Flour 1 can (12 ounces) tomato sauce juice from 2 to 3 lemons

Salt and pepper 1 tablespoon dried mint leaves Oil

Moisten the bread with a little water then squeeze out water and crumble bread into bowl with beef, parsley garlic, 1 tablespoon mint, paprika, salt and pepper and 3 eggs. Mix well and shape into golf ball-sized spheres.

At this point the meat balls either can be broiled or dipped in 2 or 3 beaten eggs and then coated with flour and sauteed in hot oil. If sauteing, use enough oil to lightly cover bottom of heavy skillet and brown meat balls on all sides. Drain thoroughly on paper towles.

For the sauce, combine the tomato sauce with juice from 2 to 3 lemons, coarsely cut up rind from the lemons salt, pepper and 1 tablespoon mint leaves. Bring sauce to boil; add browned meat balls and simmer over low heat about 30 mintues. TORTILLA DE SPINACA (Spinach casserole)

(12 servings) 6 packages frozen spinach, defrested 10 slices whole what bread 1 head of garlic, peeled and finely chopped 2 bunches spring onions, thinly sliced 1 pound mushrooms, chopped 2 tablespoons safflower oil Sald and pepper to taste

1 tablespoon dill weed 2 1/2 teaspoons oregano 1 teaspoon nutmeg 1 teaspoon paprika 1 tablespoon dried mint leaves 6 eggs, lightly beaten 1/2 cup grated Parmesan cheese 1 cup cornflakes Oil

Defrost spinach and squeeze out juices; reserve the juices. Moisten bread with water, then squeeze out water. Saute the garlic, spring onions and mushrooms in 2 tablespoons oil until onions begin to soften. Add the salt and pepper, dill, oregano, nutmeg, paprika and mint and mixwell. Remove from pan. Add a little more oil and saute the spinach for several minutes. Combine the spinach with the bread, sauteed garlic mixture, eggs and cheese and 1 1/2 cups of spinach juices, enough to make loose mixture. Mix well. Oil a 3 or 3 1/2 quart shallow baking dish and spoon in spinach mixture. Sprinkle over the cornflakes and dribble on a little oil. Bake at 350 degrees for 40 to 50 minutes, until mixture is bubbly and firm. At the end the dish may be run under the broiler for a minute to make it crisp. Cut into squares and serve hot as a side dish or cold as an appetizer with feta cheese, tomato and onion slices, Greek olives and Greek bread. RICE PUDDING

(Serve 6) 4 cup milk, scant 2/2 cup rice Peel of 1 lemon, coarsely cut up 1 cinnamon stick 1 vanilla bean 2/3 cup sugar, heaping pinch salt

Pour milk over the rice and allow to soak for two or thee hours. Add the lemon peel, cinnamon stick and vanilla bean and cook in heavy pot over low heat, uncovered, until milk is absorbed and rice is soft, about an hour or so. Stir occasionally. Fifteen minutes before rice is done, add the sugar and continue cooking, stirring until mixture is creamy. Chill and serve.

The following recipe, for Pinonato , comes from the island of Rhodes in Greece. It is very similar to a Jewish recipe called taiglach ; little pieces of dough cooked in honey. The directions for adding the flour are somewhat vague because Clapp says you must feel the dough. PINONATO

(Honey Cooked Dough) 4 eggs, well beaten 2 1/2 cup flour, approximately 1 cup sugar 1 cup honey 1 teaspoon rosewater 1 cup water

Beat the eggs in large bowl; continue beating as you add the flour, until dough is too thick to be beaten. Continue adding flour, using your hands to work it in. Add enough flour so dough doesn't stick too much. Knead it until it works easily and becomes silky, about 15 minutes. Divide the dough into parts and roll out each part into a narrow rope, about 1/2 inch wide. Cut rope into 1/2-inch-long pieces. Keep dough which is not being worked covered to prevent it from drving out.

In a large heavy pot combine sugar, honey, rosewater and water. Cover; bring to boil. When mixture is boiling quickly add the dough pieces and cook over medium heat, covered, for 5 minutes. After five minutes open the pot, just enough to put in a slotted spoon; stir gently so dough does not break. Re-cover and cook a little longer, then stir again with slotted spoon. Be careful when you open the pot not to burn yourself. Repeat the operation until the dough is broken brown. When they are done they will be brown and puffed up a little.

Remove the pot from the stove and uncover. Immediately place under cold water faucet. Turn on faucet quickly and turn off quickly so that a little water has been added to the mixture. This prevents the honey mixture from caramelizing. Stir quickly and then transfer mixture to another pot. Cool. Serve at room temperature.