THEODORE Roosevelt was a prodigious eater. He would have been delighted to know his grandson Archie's mother-in-law.

When Lucky Roosevelt's mother, Najla Showker, is in residence at the Roosevelt's Georgetown home, it's worth canceling whatever else you are doing if you receive an invitation to share a meal. You are in for a Lebanese feast which you won't find easily elsewhere in Washington.

Mrs. Showker was born and raised in Lebanon but has spent almost all of her adult life in Tennessee. You might have thought that it would be impossible to buy sesame paste, cracked wheat and yogurt in Kingsport, Tenn., 50 years ago, and that Mrs. Showker would have learned how to cook American food instead. You would be right on both counts. But anxious to have her family know the food of her own childhood and her husband's, Mrs. Showker imported everything she needed from New York.

Today the exotic ingredients are no longer exotic, and are available in Tennessee just as they are throughout the country.

Lucky Roosevelt remembers that everything she ate as a child was fresh. "We were all brought up to be good cooks. My sister," she said as she helped her mother prepare a lunch for 18 guests, "is an excellent cook."

"I think it's a pity not to enjoy cooking," her mother added as she arranged the okra. "When I started I didn't know how to fry an egg."

But when she came to America as a very young bride she did know how to speak English, as well as French. "When I came there I spoke the language, better than some of the people living there did." By the time she was 36, Mrs. Showker was president of the Tennessee League of Women Voters, and when her husband died she went to college. By 1964 she had progressed to her Ph.D. orals and went on to teach back in Tennessee, retiring last year.

She did not, however, return to cooking again on a daily basis, just for special occasions. But she makes sure there are a lot of special occasions for cooking. "I entertain a lot. I know I'd never cook for myself. I'm very busy. I don't have a minute."

Lebanese are known for their hospitality. One mark of it is the lavish display of appetizers they offer guests. Even though the meal at the Roosevelts' was lunch, there were two wonderful dishes passed with cocktails before the guests sat down: baba ghanouj (eggplant with sesame paste) and deep fried cauliflower dipped in tahini (sesame paste).

The meal, served from an amply filled buffet table, was what the untutored might call Lebanese. Mrs. Showker says she doesn't know what Lebanese food is. "I don't think I know of anything that I would call Lebanese. It's Middle Eastern. Lebanese love good food. There's a great deal of French influence because they've been there since the Crusades."

Lebanon has long served as a cross-fertilization point for East and West. Until the latest devastation, Beirut was considered the culinary capital of the Middle East. One could find food from every continent in its restaurants. But those who have been there say the best food in Beirut is the Lebanese version of Middle Eastern dishes. And the most advanced form of the art is the mezze, an hors d'oeuvre table covered with anywhere from half a dozen to 50 dishes.

Some of the dishes Mrs. Showker served for lunch would find their way to a mezze, especially an extended one: Not only the baba ghanouj and cauliflower dishes, but the hummus bi tahini (chick peas and sesame seed paste) and tabbouleh (cracked wheat salad), chicken and rice, stuffed squash, kibbe (lamb or beef and cracked wheat), green beans and tomatoes, salad, Arab bread (pita) and an okra dish that can turn okra haters into okra lovers. The secret to getting the gumminess out of the okra? Partially baking, frying or broiling the okra before using it in a dish, Mrs. Showker explained.

Tahini is the most important ingredient in Arabic cooking. A paste made from sesame seeds, it can be served with vegetables, fish and chicken. It is used not only as a dip, but as an integral part of many, many dishes. Kibbe, which is prepared in several ways and served cooked or raw, is virtually the national dish of Lebanon, where it is made with lamb. Mrs. Showker says Americans prefer beef. The cracked wheat bulgur used in the dish should be finely ground. It comes in coarse and fine grind.

The dishes are quite uncomplicated. "We don't use a lot of spices," Mrs. Showker said. "I have a feeling people use a lot to cover bad food. We only use a lot of cumin."

Most Lebanese also use a lot of garlic, but Lucky Roosevelt doesn't like it so you will not find it in the recipes where it is traditionally used, the hummus and baba ghanouj.

With or without garlic the Lebanese feast made the kind of hit few meals do in Washington. Almost everyone, including the chic and svelte women who count their calories, asked for seconds. OKRA MOLD (Falib Bamia) (20 people as side dish) 6 boxes frozen okra, slightly defrosted 6 tablespoons melted butter 1 tomato, peeled and cut into petals 1 large onion, chopped 2 tablespoons butter 28-ounce can tomatoes Salt and pepper

Place the okra on two jelly roll pans. Drizzle with butter. Bake the slightly softened okra at 500 degrees for 15 minutes; don't let them brown. In a 3- or 4-quart casserole lined with foil, arrange the okra like the spokes of a wheel. Place the tomato, opened to look like a flower, in the center. Fill in the holes with smaller pieces of okra. Cover the tomato with okra. Saute the onion in the butter. Spread the sauteed onion over the okra and tomatoes. Spoon on half the can of tomatoes. Top with another layer of okra arranged like the spokes of a wheel. Top with remaining tomatoes. Season with salt and pepper. Refrigerate if desired. To serve, if refrigerated, let sit at room temperature for 30 minutes. Cook on top of stove and simmer for 20 to 25 minutes, until mixture is hot and bubbly. To serve, unmold by turning upside-down on serving plate. Remove foil. STUFFED SQUASH (20 servings) 26 small yellow crookneck squash 3/4 cup pine nuts 6 tablespoons butter 2 medium onions 3 pounds ground beef Salt and pepper to taste 16-ounce can tomatoes

Wash the squash and cut off the necks. Scoop out the inside. Line a 6-quart pot with foil. Brown the pine nuts in the butter. Add the onions and beef and brown. Season with salt and pepper. Stuff each squash with this mixture and place in lined pot. Place the big ones on the bottom, the smaller ones on the top. Pour on the tomatoes and 1 can of water. Season with salt and pepper. Refrigerate, if desired. To cook, cover and cook slowly for first 30 minutes. Raise heat and cook quickly for about 10 minutes; reduce heat and cook slowly for another 20 minutes or so, until squash are tender but not falling apart. Serve sauce separately.

Squash is also good served with plain yogurt. TAHINI 1 1/2 to 1 3/4 cup tahini (canned sesame paste) Approximately 1 cup water Approximately 1 cup freshly squeezed lemon juice 2 teaspoons olive oil

Beat the tahini until smooth. Add 1/3 cup water and mix; add another 1/3 cup and mix. Add as much more water as you need from the cup to make a very stiff paste. (Water stiffens sesame paste; lemon juice thins it). Then start to add the lemon juice. Add 1/2 cup and mix well. Add 1/4 cup and keep stirring. Add more of the remaining lemon juice until mixture is thickness of medium cream sauce, but err on the side of thickness. Stir in the olive oil. BABA GHANOUJ (20 servings as hors d'oeuvre) 3 slender medium-large eggplants 3/4 cup tahini (canned sesame paste) Salt Lemon juice Chopped parsley Pomegranate seeds

Slash each eggplant in three places to keep from exploding. Bake at 400 degrees until soft, 45 to 60 minutes. When cool enough to handle, peel and puree the inside, adding salt to taste. Mix with tahini and adjust seasoning. You may want to add some lemon juice. Chill. To serve, spoon onto large shallow serving dish; decorate with parsley and pomegranate seeds and serve with triangles of toasted Arab bread. KIBBE (20 servings as one of several dishes) 2 cups raw, fine cracked wheat 1 large onion, chopped 1/3 cup pine nuts 1 teaspoon (heaping) cumin 1 tablespoon dry mint, crushed Salt and plenty of pepper 2 pounds ground beef

Soak the cracked wheat in cold water, for 30 minutes at the most; drain and squeeze out water. Place chopped onion, pine nuts, cumin and mint with a little water in blender or food processor and process to a paste. Season with salt and pepper. Mix this paste with the beef, working in with fingers. Add cracked wheat and mix well. Adjust seasoning and chill. Serve with triangles of Arab bread.

Note: This recipe is for kibbe served raw, but it is often served cooked. Spread in a flat pan and bake at 350 degrees for 35 minutes. Serve hot or at room temperature.