For centuries, mussels have been eaten and relished all over Europe, but it wasn't so very long ago that they were virtually unknown in this country. They were here, growing in profusion in coastal waters all around the country, but unless someone noted their occasional appearance on the menu of a sophisticated restaurant, nobody ever thought of eating them.

Mussels, which grow in tidal areas, clinging to rocks, pilings and anything else they can get a grip on, are easy to gather, very prolific and can be harvested year round, so they have always been inexpensive. They have been cultivated for generations in other countries and yet have been neglected here.

In the '70s, with the increase in international travel, Americans abroad became enamored of mussels, and mussel dishes began showing up in restaurants around America. Now, with vast amounts of mussels being produced by aquaculture, they are also commonly available at fish shops and supermarkets.

In Sicily, where I first learned to appreciate mussels, little waterfront restaurants keep thick ropes encrusted with live mussels, as they come from the mussel farms, dangling in the water where they stay plump and fresh. When a group of diners orders mussels, the waiter hoists a rope, heavy with the shiny black mollusks, out of the water, weighs it and charges by the kilo, rope and all.

The rope goes to the kitchen and in the time it takes to sip a glass of wine, the waiter is back with steaming bowls of mussel soup, redolent with fresh herbs, garlic, wine and a hint of saffron, and a basket of crusty bread to mop up the juices.

Though mussel soup has long been Mediterranean peasant fare, the recipe below, which I encountered in a coastal Corsican village, elevates simplicity to celestial heights with the addition of cre`me frai~che.

One of the most sumptuous foodstuffs known to man, cre`me frai~che simultaneously enriches and mellows the flavors of the soup, making it an elegant entree for light entertaining.

Accompany it with a loaf of crusty French or Italian bread and a plate of sliced, sun-ripened tomatoes drizzled with fruity olive oil and strewn with shredded fresh basil leaves and cracked malabar pepper. Open a chilled bottle of hermitage blanc or a good white burgundy and bask in the memorable flavors of a Mediterranean summer.

HERBED MUSSEL SOUP WITH CREME FRAICHE (4 servings)

1/2 cup dry white wine

4 pounds mussels, scrubbed and debearded

2 tablespoons unsalted butter

2 tablespoons fruity, extra-virgin olive oil

2 cloves garlic, minced

1 cup carrots, peeled and cut in 1-inch julienne

1 cup celery, cut in 1-inch julienne

1 leek, trimmed, washed and cut in 1-inch julienne

1 medium onion, peeled, trimmed and cut, lengthwise in 1-inch julienne

1 cup ripe tomatoes, peeled, seeded and chopped

6 cups fish stock

1/2 teaspoon saffron

2 ounces cre`me frai~che

3 or 4 tablespoon mixed fresh herbs including basil, tarragon, flat leaf parsley, thyme, summer savory or oregano

Salt and freshly ground pepper to taste

In a heavy bottomed pan, large enough to hold the mussels, bring the wine to a boil. Add the mussels, cover, and cook, shaking the pan frequently until the mussels have opened.

Remove the mussels from the pan, discarding the shells and reserving and straining the liquid. Heat the butter and oil in a heavy skillet and saute' garlic 1 minute. Add the vegetables and saute' until tender.

Bring the stock to a boil in the same pan the mussels were cooked in. Add the saffron, vegetables and mussels and cook until heated through. Do not boil. Remove from the heat. Combine the cre`me frai~che and mussel cooking liquid and stir into the soup, along with the fresh herbs and salt and pepper to taste. Serve immediately.