CONSIDERING how easy sorrel is to grow, and the unique lemony taste it gives to soups and sauces, it's astonishing that it isn't more familiar to American cooks. People who grow up in the country often know it as a weed, the fragrant "sour grass" one nibbles on a warm summer day.

The French have a variety of uses for garden sorrel, a milder member of the dock family, which resembles spinach in appearance and has a gentle enough taste to be included in lettuce salads. French chefs enjoy inventing sorrel sauces to serve with fish and veal, relishing its flexibility as an herbal counterpart to lemon.

There is no more elegant way to start a meal than with sorrel soup, which is easy to prepare in any of its various manifestations. It takes two minutes to melt fresh sorrel into a puree suitable for an omelette, and finished off with a little heavy cream, sorrel puree is refreshing as a side dish for grilled pork chops, a bed for poached eggs or (combined with herbs and lemon juice) a stuffing for baked fish. Mixed with spinach, sorrel provides the flavor for an unusual souffle.

Sorrel is still considered fairly exotic in this part of the world, but local cooks should do something to correct this. In addition to being east to grow and prepare, sorrel is loaded with Vitamin A and other nutrients.

Naturally you can't cook what can't buy, and you won't find sorrel at supermarket produce counters -- yet. But from April through the summer it is available from quality greengrocers such as Hudson Brothers (3206 Grace St. Nw, in the Georgetown Market) and Sunrise Produce (13224 Fifth St. NE, in the Washington Market) If you have even a tiny spot for gardening however, you should consider growing your own, because this hardy perennial grows like a weed as long as it is kept moist. (Plant it in partial shade.)

Out of curiosity, I bought a sorrel plant at the Cathedral Greenhouse early last summer, tried a recipe or two, developed a following among the toughest of critic (food snob friends and conservative 8-year-olds) and went back for two more plants. Three plants kept out family in sorrel soup at least once every two weeks through the summer and spring. The plants survived the winter and are producing better than ever (The Greenhouse is located behind the Washington Cathedral, on Wisconsin Avenue half a block above Massachusetts. Call first, 537-6258, to be sure they have stock.) Seeds are available from mail-order firms such as J.A Demonchaux Co., 827 N. Kansas, Topeka, Kan. 66608.8.

Hudson Brothers is currently selling sorrel at $1.50 a pound, but a pound of sorrel is a lot of sorrel. One pound untrimmed provides about 10 cups of usable sorrel, and half a pound is more than enough for sorrel soup for six.

To prepare sorrel for cooking, wash in cold water and, using a sharp knife, cut off the white stems and central rib removing any bad spots. Roll a few leaves into a cylinder shape and cut them cross wise into thin strips, referred to as chiffonade . To produce a sorrel puree, heat the chiffonade in butter (a tablespoon per packed cup of sorrel) until it softens and turns a darker green. This may take less than a minute. A cup of sorrel produces about 2 tablespoons of puree. For some dishes you will want to bind the melted chiffonade with a little thick cream. Always cook sorrel in a stainless steel or enamel pan; it contains oxalic acid, which reacts badly with many metals.

These recipes show how sorrel lends itself to variations on a theme. Each of these soups is, in its own way, a champion.

Anne Elsbree of the Cathedral Greenhouse gave us this recipe for a sorrel soup that may be served warm but is delicious cold. It is an elegant soup for an elegant dinner: GREENHOUSE SORREL SOUP (6 to 8 servings) 2 cups sorrel 3 lettuce leaves 3 sprigs parsley A few sprigs chervil or basil 1 medium onion Salt, pepper and nutmeg 3 tablespoons butter 2 tablespoons flour 2 quarts chicken or veal stock 4 egg yolks 1 cup sour cream

Chop sorrel, lettuce, parsley chervil and onion very fine. Cook with the spices in melted butter until soft and tender. Add flour, then stock, and simmer for 10 minutes. Cool slightly, then add egg yolks and sour cream. You may want to blend the soup to make it smooth (the sorrel looks stringy), but many people find the prosper of a creamy white soup boring. Serve warm or ice cold.

If you are serving sorrel soup for a dinner party, you may prefer one of the creamier, more delicate soups. But if there are children in the crowd, particulary hungry children, this hearty soup is more likely to hit the spot. Resist temptation to puree it; people who like this soup like their potato in recognizable chunks. The recipe is taken from one of the best summer cookbooks I've found: "Summer Feasts" by Molly Finn (Simon & Schuster, $11. 95). SORREL AND POTATO SOUP (6 servings) 8 to 10 scallions including green tops, sliced 3 tablespoons butter (or more) 2 large potatoes, peeled and diced 1/4 pound sorrel leaves (2 to 3 cups shredded) 3 cups chicken stock, preferably homemade salt and freshly ground pepper

Saute scallions in butter in a 3-quart pot. When soft but not brown, add the potatoes and the sorrel and toss in butter over low heat until the sorrel leaves have wilted. Add the stock, bring it to a boil, turn down the heat and simmer soup for 20 to 30 minutes, until the potatoes are done (taste one to be sure). Season to taste with salt and pepper.

This classic French cream of sorrel soup, is a thin soup, light and delicate. It's a perfect course to precede a heavy dish like duck or goose. GREEN SOUP (4 servings) 3 tablespoons butter 1/2 onion, finely chopped 2 medium-sized potatoes, peeled and diced 1 3/4 pints chicken stock 2 good handfuls of sorrel Salt, pepper, nutmeg and a pinch of sugar 3 or 4 tablespoons of cream

Melt the butter and cook the onion in it until soft. Add the potatoes and pour in the chicken stock. season well and simmer until potatoes are soft. Wash the sorrel leaves and, unless they are very small and tender, strip them off the central rib. Put the soup and the raw sorrel in the goblet of a blender -- a little of each at a time -- and reduce to a smooth cream. Reheat gently, test the seasoning, and stir in the cream. Serve garnished with tiny croutons of fried bread, or with a swirl of whipped cream sprinkled with chives topping each bowl.