Pot au Feu-two courses from a single pot, a tradition in rural France

These oldest and most popular of French dishes are indicative of Gallic thrift and ingenuity, although similar soups are made in many American kitchens where the cook does not even give her concoction a name.

A version of pot-au-feu was made by early settlers in this country. When they had nothing in particular for dinner except what was in the root cellar, they might say ''we'll just boil pot for today.''

A piece of salt beef was put into an iron pot with all the vegetables at hand and boiled until the beef was tender. Then the meat was served on a platter with the vegetables arranged around it.

It is still served this way in the peasant homes of France. You may like to serve it with vinaigrette, or mustard and coarse salt.

After the meat has been brought to a boil and all the fat skimmed off, the vegetables and herbs that give flavor are added and the whole simmered together for several hours.

This is important to the perfection of the dish, which makes it ideal to prepare in a slow pot cooker.

One common recipe calls for leeks, carrots, turnips, celery, onion, parsley, 5 cloves, a pinch of thyme, sweet marjoram and bay leaf, but there are all sorts of variations.

The stock, broth, consomme or bouillon is served as a soup with some added flavor . . . chicken, celery, onion or whatever suits.

Another name for Pot au Feu is Petite Marmite. A marmite is an earthenware lidded pot, higher than it is wide. The material from which it is made is in part responsible for the flavor of the soup. In restaurants Petite Marmite is served with toasted bread floating on top. France's ''Pot au Feu'' 1 pound meat bones 21/2 pounds beef, cut 2 small carrots 1 medium turnip 1 small parsnip 3 quarts water 3 leeks 3 onions 6 whole cloves, stuck into 1 onion 1 celery rib 1 large bay leaf 1 sprig thyme 8 sprigs parsley Salt to taste

Cover bones with water. Boil, skimming away the scum as it rises. Simmer 3 to 4 hours. Strain through cheese cloth and cool overnight. Remove fat. Put meat in saucepan with the stock. Heat to boiling and skim.

Wash, peel, and slice vegetables. Tie bay leaf, thyme and parsley together. Add vegetables, salt, and herbs to the stock. Cover saucepan. Tilt lid to allow steam to escape. Simmer gently 31/2 hours until meat is tender.

Remove meat and reserve to add stock later. Strain stock through a wet towel. Cool stock. Use as desired for making stock soups, consomme, sauces. Serves 8 to 10. Pot au Feu (Slow Cooker Method) 3 pounds rump roast, chuck pot roast, bottom round or sirloin tip 4 chicken wings or equivalent in chicken necks, backs, and gizzards 3 large carrots, scraped and quartered 3 medium young white turnips or 3 parsnips, scraped 3 large stalks celery, cut into 4-inch pieces 1 10-ounce can beef bouillon or 10 ounces water and 2 beef bouillon cubes 1 small onion, peeled and stuck with 4 whole cloves 1 large bay leaf 6 sprigs fresh parsley or 1 teaspoon dried parsley 1/2 teaspoon ground thyme 4 cloves garlic, peeled (optional) 8 peppercorns 2 to 3 teaspoons salt (preferably sea salt or coarse kosher salt)

Place all ingredients, except salt, in slow cooker, with vegetables and herbs on bottom. Cover and cook on Low for 12 to 18 hours.

Discard chicken pieces. Serve from a tureen into soup dishes. Serve salt on the side to be sprinkled over the meat by each diner before eating. If desired, serve in soup bowl with big chunks of crusty French bread. Serves 6.