BEAN sprouts have gone the way of the American hippie -- right into the mainstream.

No longer are sprouts solely a key component of earnest communal meals; now they are popping up everywhere, from elegant sandwiches and salads to interesting entrees and vegetable dishes. They're a way to grow and serve fresh, living vegetables even if you have no garden plot. But the cook who prepares them always ought to remember that their flavor, texture and nutritional content depend on their being eaten alive.

A sprout is that tender limbo stage between a seed and a plant. It's alive and always changing, pulling out food reserves packed into the seed and mobilizing them until the plant has grown big enough to photosynthesize and make its own food.

Germination begins when the seed soaks up water, which is why you begin sprouts at home by soaking the seed. The water softens the seed coat, and it filters into the plant embryo, whose cells begin to elongate and divide. Most of the seeds we choose to use for sprouting grow fast on the root end, and soon the growing root, or radicle, breaks through the dissolving seek coat. But to keep on growing, a sprout needs air as well as water -- which is why, after a night of soaking, you pour off the water and let sprouting seeds drain.

Living sprouts slough off cells as they grow. So they need to be rinsed regularly to cleanse this accumulation from them. The faster sprouts grow in these first days of life, the more water they use, the more cells they lose, and the more rinsing it takes to keep them fresh and healthy.

Temperatures have an influence on sprouting seeds. Counter-top sprouting takes longer in winter, and some summer days may get too hot to sprout. The seeds take in water and throw out new growth so fast in hot weather that it's hard to keep them rinsed as often as needed. Unrinsed sprouts turn brown at the root end, indicating inadequate breathing space and nourishment for the plant. Sprouts will grow more slowly if kept in the refrigerator, but they still need regular rinsing; they still need life-respecting care.

Standing water and overcrowding threaten sprout life just as much as too much growth too fast. The seeds need to stand that first night in water to break into the tough seed coat, but from that point on in a sprout's existence, water can suffocate. A jar full of sprouts must be rinsed with fresh, cold water at least once daily, and that way you'll leave enough moisture clinging to the sprouts. But always drain the excess water. Even if you leave sprouts in the refrigerator to last a bit longer, rinse and tip them to avoid their turning brown at the ends. Too dense a sprout population can suffocate them, too, a detail hard to remember when you're pouring out a mere spoonful of dry little seeds into a quart jar for sprouting. But in three springtime days, a tablespoon of alfalfa seeds nearly overflows a quart jar.

Treat store-bought sprouts similarly. Don't leave them in a container where they can't breathe. If they came in the container in which they were sprouted, give them a rinse and let them drain adequately. If you bought them in bulk and brought them home in a plastic bag, put them in a quart jar with a mesh top on it (a swatch of nylon hose works fine). Rinse them and tip them to drain, and keep them draining in the refrigerator. Rinse them at least once a day thereafter.

Traditional cooks in Chinese cuisine use only the radicle, or growing root end of the sprout. In Britain, making sprouts means planting mustard or cress seeds in a growing medium, then in a week clipping off the green shoots or cotyledons, to spinkle as a garnish on salads. But American tradition calls for root, shoot, seed and all -- a tradition that makes for coarser, crunchier, and more nutritious sprouts than either foreign practice. The nutritive value of sprouts depends on whether the seed is attached or not," says nutritionist Ruth Matthews of the USDA, suggesting that sprouts eaten seed and all provide the most food value.Matthews is supervising the laboratory research going into the forthcoming revision of the USDA's "Handbook of the Nutritional Composition of Foods," due for sale from the GPO later this year. "This is the first time that sprouts will be included in the vegetable section of the handbook. We have been besieged by calls asking for the nutritive value of sprouts."

Lab researchers working for the USDA have discovered several curious details about the nutrition of sprouts, including the fact that Vitamin A content is higher when sprouts are grown in daylight rather than in the dark. Trace amounts of minerals -- calcium, iron, magnesium, phosphorus, potassium, sodium, zinc, copper and manganese -- also have been measured in alfalfa sprouts, but as Matthews says, "You have to eat a lot of sprouts to get a significant amount of the nutrients. Still, they certainly contribute."

Other tests have found high levels of saponin in alfalfa sprouts. Saponins are naturally occurring plant-produced detergents that can destroy red blood cells and would be harmful in large quantities. A pinch of alfalfa sprouts on a salad or sandwich won't cause difficulties, but relying on alfalfa sprouts as a major protein source might.

Sprouts are traditionally used raw, tucked into sandwiches or scattered in a salad bowl. But sprouts can be used in cooking too, as long as you keep them crisp and tasty by following these two rules: 1) Cook them very briefly, either in a stir-fry or in a hot oven, 2) When baking, cover them with other ingredients so they do not remain exposed to the heat. They can substitute for common ingredients in favorite recipies, like ground meat in lasagna. Or you can create new recipes just for the sake of sprouts. HERB AND SPROUT CASSEROLE (4 servings) Olive oil to grease casserole pan 3 cups cooked rice 1 1/2 cups fresh sprouts 1/4 teaspoon rosemary 1/4 teaspoon sage Dash of worcestershire sauce 1 cup grated muenster cheese 1 tablespoon parmesan cheese

Oil 1 1/2-quart casserole, then layer in ingredients in the following order: 1 cup rice, 3/4 cup sprouts, pinch of herbs and dash of worcestershire, 1/2 cup grated muenster. Repeat layers once again, then top with one more layer of rice, sprinkle on parmesan and another pinch of herbs and worcestershire. Bake 15 minutes at 425 degrees. SPAGHETTI ALLE GERMOGLIE (2 servings) 1 teaspoon butter 1 tablespoon olive oil 4 scallions 8 mushrooms 1/4 teaspoon thyme 1/8 cup grated fresh parsley 1 handful pasta (enough for two) 1/2 cup grated parmesan or romano cheese 1/2 cup fresh sprouts

Melt butter, add oil, then simmer sliced scallions, slice mushrooms, thyme and parsley, until softened. Cook pasta until al dente. Strain and toss in serving bowl with scallion and mushroom mixture, grated cheese, and fresh sprouts. Serve immediately. BURRITOS CON VASTAGOS 12 flour burritos 2 fresh tomatoes, chopped 2/3 cup fresh sprouts 1/2 pound monterey jack cheese Hot pepper sauce

Into each burrito, spread (in this order): chopped tomatoes, sprouts and grated cheese; top with a dash of hot pepper sauce. Roll tightly and lay side by side in shallow baking pan. Bake at 425 degrees for 5 minutes. Serve immediately. SPROUTING YOUR OWN

* Buy seeds specially for sprouting. Try alfalfa, mung beans, radish, or chickpeas first; then advance to soybeans, lentils, wheat or sunflowers.

* Use 1 tablespoon of tiny seed, 1/4 cup of larger seed. Soak overnight in a wide-month quart jar with at least four times that amount of water.

* Next morning, drain off water through screen or cheesecloth attached to jar rim. Tip jar upside down and balance in bowl to catch excess water. Be sure to allow air circulation. Leave jar in cool, dark, draft-free place.

* Over next few days, rinse sprouts one to three times daily, depending on temperature and seed size. Higher temperature and larger seed calls for more frequent rinsing.

* Sprouts may be eaten at any point in process; five to seven days after start will result in optimal nutrition. Thereafter, keep rinsing sprouts but set jar in refrigerator to halt growth.