The beach cleanup crews call it trash. Scientists call it marine algae, nature food stores call them edible sea vegetables. Food processors call them marine colloids. Hawaiians call it limu and buy it fresh in their grocery stores.

Whatever they call it, it's just seaweed. Interest in seaweed is growing for several reasons -- the popularity of Japanese restaurants, the increase in vegetarians, a growing population of Asian immigrants accustomed to sea vegetables, and indications that elements of a macrobiotic diet help prevent certain forms of cancer.

Sea vegetables are rich in vitamins and minerals, low in calories, easy to digest, and now they are readily available in dried form in oriental markets and health food stores.

But there is another source of fresh seaweed, the beach, where seaweed is available for the vacationing cook with an esoteric sense of curiosity, the beachcomber who needs a purpose for the dawn stroll, or the romantic who feels the primordial tug of the tides and sea currents that link the continents.

The Atlantic shores have been shortchanged when it comes to seaweed, except along the rocky Maine coast where several varieties of edible seaweed are commercially harvested or gathered by amateur seaweed aficionados and vegetarians. But seaweed does appear sporadically on the Delmarva shores, the Carolina beaches and the warmer waters of Florida.

The southern waters don't have the dulse and kelp of the colder waters or Maine's sea-tangy rockweed, the weed used to pack lobsters and put in the pot for clambakes. But it is there for the adventurous and curious.

Sargassum floats in occasionally to the mid-Atlantic shores in late summer or after a wrenching storm. This is the brown alga with the golden berries -- these are little carbon-dioxide filled bubbles that let this alga float literally from continent to continent.

Occasionally the mid-Atlantic shores have the bright and light green sea lettuce. This is prized as a food in Hawaii and the Orient, but used here mostly as decoration for Florida salad bars. Sometimes a storm will rip loose the subtidal seaweed far offshore and present to the beachcomber a little reward -- a lush species of red algae.

Sometimes it is only the cane grasses that are washed out of the salt marshes and into the sea, a curse for the shore fisherman who must strip them from his line before casting again. These aren't seaweed at all and aren't edible.

There is just one way to know whether you have an edible sea weed, and that is to taste it. Go ahead. This is not like the forest, where you can get in real trouble eating something unknown. (More about that later.) You will find out in a hurry if you have something you want to add to a salad or flavor a soup. Some are tough and need cooking. Others are tender and crisp as a piece of celery.

Trying to describe the taste of seaweed is quite maddening. There is a tendency to try to compare them to land plants. Judith Cooper Madlener, who wrote "The Seavegetable Book," a marvelous, comprehensive look at seaweed, says, "The algal flavors are not salty or fishy as might be expected; some might be described as beanlike, nutlike, or even as reminiscent of celery, parsley, or even grapes. There are . . . no popularly recognized terms to describe the unique flavors."

There are several ways to do a seaweed search. The easy way is to walk the beach. Each year, mysteriously, something new seems to appear. After a storm is a good time to look. If something is floating in, swim out and gather it while it's still clean in the sea. If you find it on the beach, or growing on rocks, it may be mixed with sand and bits of sea trash and it will take more rinsing.

If you're a snorkeler, you can take a look farther out in the subtidal zones. Even if you have a clean sandy shore, there may be concrete pilings or jetties where seaweed have taken hold. But there are cautionary rules. It is safest to search in protected coves and shallow bays. Stay out of polluted areas, busy harbors and boating lanes, and don't work under bridges or exposed coasts where there is a surf. You can get slapped by the surf onto rocks. And, as in any swimming, always have a buddy.

Much of the search is done by feel. Run your hand below the tide line where you find something growing. Usually it will be soft. And squishy. But if you feel something wiry and more resiliant, you may be onto something.

First rule for the seaweed gatherer: Don't take the holdfast. That is the part of the plant that is attached Cut above the holdfast by several inches, if possible, to allow the plant to continue growing.

Another rule, never take more than you can use. If you want to gather enough for dinner, take along a pail to the beach and cover the plants with sea water. If you're working in the water, the best thing is a net bag with a drawstring, which you can tie to your belt or swim suit and keep the plants fresh. Low tides may reveal plants in the intertidal zones. Be especially vigilant when exceptionally low tides are expected.

A book is helpful not only for identification but for information about harvest seasons, knowing which are the tastiest parts of the plant, methods of preparation and storing for different plants.

About the possibility of toxic plants. According to Madlener, nobody has ever had a lethal dose of seaweed. There are only a couple of toxic varieties and it is very unlikely that the average beach-forager would come upon one. There is an uncommon brown alga called desmarestia, which contains sulfuric acid, tastes like sour lemons and would cause severe stomach upset. The other variety is not one anyone attempts to eat. It is called Mermaid's Hair and is a bluish-green scum found floating at the base of mangrove roots. There is a legend about a lethal species growing in one spot of Hawaii but we won't worry about that.

There are several good resources; some are out of print but available from libraries: Madlener's "The Seavegetables Book" (Crown, 1977, $5.95), "Food Power From The Sea," by Leland Fryer (Mason/Charles), "Cooking With Sea Vegetables" by Sharon Rhoads (Autumn Press) and "The Limu Eater: A Cookbook of Hawaiian Seaweed" by Heather Fortner (U.S. Department of Commerce National Technical Information Service, PB-295 327).

Fortner gives these tips on cleaning seaweed: Roll it between the hands while running water over it. She also puts it in a mesh bag and uses a hose. Even a session in a washing machine on the rinse cycle can help shake loose the detritus.

No matter how you do it; the important thing is to get out the sand. HEATHER FORTNER'S LIMU NAMASU SALAD (8 servings)

Fortner, who lives and works as a fisherman aboard the NOAA ship Miller Freeman operating in Alaskan waters, showed up at a potluck dinner on South Padre Island, Tex., this summer bearing a limu (the term used by Hawaiians for all seaweed) salad. Fortner had found gracilaria growing below the low-tide line on an offshore concrete piling, a relic of a pier that didn't survive a hurricane

The gracilaria was mixed in with several other mossy, stringy weeds and not instantly recognizable as something you would want to find in a salad. But it was delicious. A brown alga, gracilaria tastes slightly sweet, piquant and salty, with a definite celery flavor and crunch. It is a prized seaweed in Hawaii.

4 cups fresh gracilaria, washed and wilted*; or 1 ounce dried hijiki; soaked 30 minutes in cool water, or 2 cups celery, sliced into strips

1 sweet onion, (red, Maui or Vidalia preferred), sliced into strips

2 firm tomatoes, peeled and sliced into strips

1 large cucumber, peeled (if waxed) and sliced into strips

FOR THE NAMASU DRESSING:

1/2 cup corn oil

1/4 cup apple cider vinegar

2 slices fresh ginger, about size of a nickle; peeLed

2 cloves whole garlic

2 teaspoons worcestershire sauce

2 tablespoons sugar

Salt and pepper

Louisiana hot sauce

In a salad bowl, combine vegetable strips. Combine dressing ingredients and pour over vegetables. Cover, refrigerate and marinate 3 hours. Drain, toss and serve.

*To wilt seaweed: Pour hot water over cleaned seaweed for about 30 seconds. The water should not be boiling hot, or it will turn the seaweed to mush. Gracilaria will turn dark purple. Other seaweed turn other colors when wilted. DULSE CHOWDER (8 servings)

Dulse, a red alga harvested in Maine and Grand Manan Island, New Brunswick, Canada, is one of the most popular of the seaweed sold in health food stores. It can be eaten as a snack out of the package or shredded as a seasoning for soups, salads or rice.

This soothing soup is a low-calorie, nutritious alternative to clam chowder. It is a good way to use leftover nori after making sushi.

2 1/2 cups sliced onions

2 cups diced celery, stalks and leaves

1/2 ounce or 1 cup dried dulse, shredded with scissors; or toasted nori

2 tablespoons light cooking oil

2 quarts water

3 medium potatoes, diced (peeling optional)

2 tablespoons chopped parsley, plus some for garnish

Salt and pepper to taste

In a heavy kettle, saute' onions, celery, dulse (or nori) in oil for 5 minutes or until vegetables are soft. Add water, potatoes, parsley, salt, and pepper. Bring to a simmer and cook for 20 minutes or until potatoes are tender. Pure'e 2/3 soup in blender, mixing with rest for texture. Garnish with chopped parsley. Adapted from "Sea Vegetable Gourmet Cookbook and Forager's Guide," by Eleanor and John Lewallen, P. O. Box 372, Navaroo, Calif. 95463. EUELL GIBBONS' STOVE TOP CLAM BAKE WITH SARGASSUM (4 servings)

The late Euell Gibbons was the one who started all this with his books about foraging for food in the fields and along the shore. He became interested in seaweed in Hawaii, enjoying the oriental uses for it. Returning home, he worked out many seaweed recipes from the six varieties he found in his tidepool in Maine. Gibbons said he always traveled with a canning kettle. He did this clambake on the small stove of a rented cottage. Gibbons had rockweed. It is not only a steaming agent but it adds its own sweet flavor to the seafood.

We adapted the recipe, substituting sargassum for rockweed. It doesn't have the same flavor, but it is a steaming medium and does have some flavor. We checked first with Dr. Robert Vadas, a phycologist (alga botanist) at the University of Maine, Orono. He couldn't think of any reason why sargassum wouldn't be a perfectly adequate substitute for rockweed for this purpose.

Rockweed, sargassum (or kale), for the steaming agent

4 baking potatoes, washed, pierced

4 ears corn (leave on inner husks, save outer husks, remove corn silk)

1 pound shrimp in the shell

3 dozen steamer clams (or more)

1 pound fish fillets, wrapped in corn husks

Melted butter for serving

Lemon wedges for serving

Louisiana hot sauce (optional)

Fill steaming kettle about 1/2 or 1/3 full of rockweed, sargassum (or kale); tuck potatoes into sargassum, cover with more weed, turn on heat, and when steaming freely, cover, and cook 30 minutes. Uncover, add corn, shrimp, clams and fish fillets. Fill to top with rockweed or sargassum. Cover and cook 15 minutes. Serve with melted butter and lemon wedges. It is optional to add hot sauce to the butter. Adapted from "Stalking the Blue-Eyed Scallop," by Euell Gibbons (David McKay Co., 1964, $5.95) CHICKEN & AGAR-AGAR SALAD (4 servings)

Made from the red seaweed, agar-agar is a freeze-dried sea vegetable extract used in several forms -- powdered, flaked or in long iciclelike strands. The powder and flake forms are nonanimal jellying agents that don't require refrigeration. The strands, after soaking, are much like Chinese cellophane noodles. They are colorless and nearly tasteless, but provide a nutritious, low-calorie, high-fiber vehicle for sauces. Not as nutritious as some other seaweeds , agar-agar still has enough minerals and vitamins to make it acceptable. Its glittery look is nice in summer salads.

1 ounce agar-agar strands*, or Chinese cellophane noodles, cut into 2-inch pieces

2 cups cooked chicken, in strips

1 carrot, cut into 2-inch-fine julienne

1/2 cucumber, peeled, seeded, cut into 2-inch julienne

1 scallion, cut into 2-inch slivers

1 tablespoon toasted sesame seeds

FOR THE DRESSING:

1/4 cup chicken broth

2 tablespoons sesame oil

1 tablespoon rice vinegar

1 teaspoon soy sauce

Soak agar-agar in cold water 30 minutes. Drain thoroughly. Combine with chicken, vegetables and sesame seeds. Combine dressing ingredients, pour over chicken salad, toss and let stand 30 minutes before serving.

*Available at Oriental markets.