BY NOW spaghetti squash is relatively common in Washington area supermarkets. Still, the sight of the golden melon-shaped winter squash elicits an occasional query about preparation techniques. People want to like it; they just aren't quite sure how to approach it.

Like all winter squash, spaghetti squash differs from its summer cousins in several ways. Summer squash is picked when immature and has a soft skin while winter squash is allowed to ripen on the vine, thus developing a hard shell. The meat of the spaghetti squash is what gives the vegetable its name. The long strands buried inside really do resemble long pasta. Moreover, these mild-flavored squash strands are amenable to a variety of seasonings, sauces and cooking methods. And yet it has barely one third the calories of its flour-based look-alike.

Consumers are likely to pay from 59 to 79 cents a pound for average three- to four-pound spaghetti squash. Most of the vegetable is edible, and one squash can easily feed four or more people, either as a vegetarian main dish or as an interesting accompaniment to meat, poultry or fish. Choose a firm, healthy-looking squash without bruises or blemishes.

Now that you have endured stares and questions at the checkout counter and your purchase is on your kitchen table, what will you do with it? You can either bake, boil or steam your squash. (Baking takes longer and requires more heat, but if your meal includes other baked dishes, put the squash in the oven with the other items.)

If you choose to boil the squash, bring a large kettle of water to a boil and fully immerse the vegetable. Cover, lower the heat and simmer 20 to 30 minutes, or until a fork inserted into the squash comes out easily. Do not overcook or the squash will become soggy. Steaming is just as effective, but it takes longer. If you bake the squash, prick the skin with a fork beforehand so it won't explode in the oven. Bake at 350 degrees from 40 minutes to 1 1/2 hours, depending on size of squash.

Allow squash to cool enough to handle; then cut in half lengthwise and remove pulpy center and seeds, just as you would a pumpkin. Discard. With a fork, rake the squash meat and scoop the spaghetti-like strands out of the shell, ready for the chef's favorite recipe. Use immediately or stored covered in the refrigerator for several days.

The most basic treatment of spaghetti squash is simply to toss the strands with butter or olive oil and top with your favorite pasta sauce: fresh tomato/herb, white clam sauce, or -- if your garden still yields fresh basil -- pesto. Or: SIMPLE SAUTEED SPAGHETTI SQUASH (4 servings) 1/2 stick butter 2 or 3 cloves garlic, minced 1/2 medium-sized spaghetti squash, boiled or steamed, with strands scooped out* 1/3 cup parsley, chopped 1/2 cup freshly grated parmesan cheese Salt and pepper to taste

Melt butter in large skillet. Add minced garlic, and cook until soft but not brown. Add spaghetti squash strands along with remaining ingredients. Heat thoroughly. When serving, pass additional parmesan cheese, if desired.

*Note: To cook, fully immerse squash in boiling water, cover and simmer 20 to 30 minutes, or until a fork inserted into the flesh comes out easily. You can also steam until fork-tender, or bake at 350 degrees for 40 minutes to 1 1/2 hours (depending on its size). Be sure to prick with a fork ahead of time so it won't explode in the oven. Allow squash to cool; cut in half lengthwise and remove pulpy center and seeds. Discard. With a fork, rake the squash meat and scoop the spaghetti-like strands out of the shell. TUNA-SQUASH CASSEROLE (4 to 6 servings) 2 to 3 tablespoons cooking oil or butter 1/2 cup onions, chopped 1 cup mushrooms, sliced 2 6- to 7-ounce cans tuna (either oil or water-packed), drained 2/3 cup green olives 2 or 3 tablespoons good quality curry powder 1 medium-sized spaghetti squash, boiled or steamed, with strands scooped out* 1 1/4 cups sharp cheese, grated 1/4 cup milk (just enough to moisten casserole) 1/8 cup grated parmesan cheese Bread crumbs for sprinkling Paprika (if desired, just for color)

Cook onions in butter or oil until soft. Add mushrooms. Heat a few minutes more, stirring occasionally, until mushrooms are soft. Add tuna, olives and curry powder. Keep at medium heat; do not allow to burn. Butter a medium-sized ovenproof dish. Place a layer of squash on the bottom and alternate with tuna mix and sharp cheese. Moisten mixture with the milk. Top with parmesan cheese and bread crumbs, and sprinkle with paprika, if desired. Bake at 350 degrees for 20 to 30 minutes or until top is brown.

*Note: To cook, fully immerse squash in boiling water, cover and simmer 20 to 30 minutes, or until a fork inserted into the flesh comes out easily. You can also steam until fork-tender, or bake at 350 degrees for 40 minutes to 1 1/2 hours (depending on its size). Be sure to prick with a fork ahead of time so it won't explode in the oven. Allow squash to cool; cut in half lengthwise and remove pulpy center and seeds. Discard. With a fork, rake the squash meat and scoop the spaghetti-like strands out of the shell. BAKED STUFFED SPAGHETTI SQUASH (4 servings) 1 medium spaghetti squash 2 tablespoons olive oil or butter 1 medium green pepper, chopped 1 small onion, chopped 2 or 3 cloves garlic, minced 1 pound Italian sausage, hot or mild, according to taste, cut in 1-inch pieces Fresh herbs: rosemary, thyme, basil, marjoram, or substitute dried herbs, to taste 8-ounce can tomato sauce Splash of red wine 1/2 pound mozzarella cheese, sliced

Cut squash in half lengthwise. Scoop out center pulp and seeds (like a pumpkin). Brush halves with oil or melted butter; bake in pre-heated oven at 400 degrees from 40 minutes to 1 hour, or until almost done. Remove from oven and allow to cool. Scoop out strands, being careful to leave squash shell intact. Meanwhile, cook green peppers, onion, garlic, sausage and herbs in a large skillet over medium heat. If particularly fatty, drain off some liquid. Add tomato sauce, swish wine around tomato sauce can and empty into skillet. Simmer at low heat until part of liquid is cooked down. Add spaghetti squash strands. Stuff into squash shells. Top with mozzarella cheese. Return to oven and bake 15 to 20 minutes or until cheese is melted. Serve with crisp green salad and Italian bread. STIR-FRIED SPAGHETTI SQUASH (4 to 6 servings) 3 to 4 tablespoons peanut oil, or enough for cooking 1/4 cup sesame seeds 1 medium sized bunch broccoli, with most of woody stem removed, and with flowerets sliced diagonally 3 or 4 cloves garlic, minced 1 1/2 bunches scallions, sliced diagonally in 1/2-inch pieces 1/2-inch piece fresh ginger root, minced 6-ounce can water chestnuts, drained and sliced 1 spaghetti squash, baked or boiled, with strands scooped out* Dash sesame oil (or more, if desired) Dash hot pepper sauce (if desired) 3 to 4 tablespoons soy sauce

Heat oil in wok. Add sesame seeds and stir until light brown, being careful not to burn them. Add broccoli, garlic, scallions, ginger, water chestnuts, and squash strands. Cook quickly at high heat, stirring constantly for 5 minutes. Add sesame oil, hot sauce and soy sauce. Serve immediately, with additional soy sauce, if desired.

*Note: To cook, fully immerse squash in boiling water, cover and simmer 20 to 30 minutes at medium heat, or until a fork inserted into the skin comes out easily. You can also steam until fork-tender, or bake at 350 degrees for 40 minutes to 1 1/2 hours (depending on its size). Be sure to prick with a fork ahead of time so it won't explode in the oven. Allow squash to cool; cut in half lengthwise and remove pulpy center and seeds. Discard. With a fork, rake the squash meat and scoop the spaghetti-like strands out of the shell.