While buying sweetbreads recently, the lady next to me in line asked what in the world I was going to do with them. The butcher was equally interested. My praise of this delicacy and my explanation of how to handle it did not erase the look of incredulity on their faces. I left echoing the TV commercial, "Try it, you'll like it," turned and said "in fact, you'll love it."

Sweetbreads may be an "offal," but are quite the opposite of the homonym "awful." They are, in fact, wonderful. Proper preparation transforms the soft, slippery raw product into a smooth, firm-textured meal that lends itself to a variety of presentations. And they will enlarge the repertoire of most cooks.

Sweetbreads are not always available at American meat counters because a large part of the American production is exported to Europe, where they are regarded as a luxury. But any meat department of a major supermarket will order them for you, given a few days notice, if they are not in stock.

Except for a paper-thin membrane enveloping the sweetbread there is no waste, so it is relatively inexpensive meat. A sweetbread weighs about one pound and is sufficient for three servings -- four servings if the dish involves mushrooms, cream and other stretchers.

First, rinse the sweetbreads in cold water. Then parboil for 8 to 10 minutes in lightly salted, boiling water, with a small onion sliced, a carrot sliced and a bayleaf. Drain and rinse under very cold water until cooled. Remove the thin outer membrane. Place a plate on top of the sweetbreads and weight it down with a heavy object. Chill for several hours. They are now ready to use according to any of the following recipes. SWEETBREADS EXQUIS (Sweetbreads With Lemon Cream) (6 servings) 1 1/2 to 2 pounds of sweetbreads Salt, pepper and flour for coating Pinch of nutmeg 3 tablespoons butter 2 tablespoons warmed brandy 1/3 pound of thinly sliced mushrooms 1/3 cup of Madeira or sherry Juice of 1/2 lemon 2/3 cup of heavy cream 2 to 3 cups of croutons, browned in butter

Prepare the sweetbreads as directed above. When thoroughly chilled, slice them. Season with salt, pepper and a pinch of nutmeg. Dredge the slices in flour to coat them lightly.

Heat the butter in a skillet, saute the slices until golden on both sides, pour on the warmed brandy and set aflame. When the flame dies out add the mushrooms and simmer for 3 minutes, stir in the Madeira or sherry and simmer for 4 minutes. Add the lemon juice and the heavy cream cook only until well blended and hot.

The whole dish and the croutons may be made as long as a day in advance and merely reheated just before serving.

Arrange the slices of sweetbreads on a platter, pour the sauce over them and arrange the croutons around the edge of the platter. Serve with a green vegetable, salad and hot rolls. SWEETBREADS AU PORTO (6 servings) 2 pounds sweetbreads Salt, pepper, flour for coating 3 tablespoons butter 1/2 pound mushrooms, sliced 1/3 cup port wine 2/3 cup heavy cream 1 tablespoon of cornstarch, if necessary

After washing the sweetbreads and parboiling and chilling them as directed above, slice them about 1/2 inch thick. Salt and pepper the slices and sprinkle lightly with flour. Heat the butter in a skillet and saute the sweetbreads until lightly golden on each side. Remove them from the pan. Put the mushrooms into the skillet, add a tablespoon of butter if necessary to keep them from sticking, cook the mushrooms for about 4 minutes, until they are just tender. Pour in the port and with a wooden spoon stir and scrape up all the brown bits from the bottom of the skillet. Allow the wine to boil up until it is reduced by one fourth. Add the heavy cream, again let it boil up until it is reduced by one fourth and is slightly thickened. Return the sweetbreads to the pan and reheat. The whole dish may be made in advance, leaving only the reheating until serving. If the sauce is too liquid for your taste, thicken by stirring in, drop by drop, cornstarch dissolved in a little cold milk. A tablespoon of cornstarch should be more than sufficient, and be careful to stir it in slowly, stopping when the desired consistency is reached.

To serve, arrange the slices of sweetbreads on a platter and pour the sauce over all. A perfect accompaniment is circles or fleurons of puff pastry. Strips of watercress or parsley and a bowl of pilaf or a wild rice mixture go very well also. SWEETBREADS GALVESTON (6 servings) 4 tablespoons butter or margarine 3 tablespoons flour 1 large onion, finely chopped. 1 cup chicken stock 1 large stalk celery, finely chopped 2 tablespoons chopped parsley 1 cup sliced mushrooms, sauteed until tender, about 4 minutes 2 pounds sweetbreads, parboiled and chilled as directed above 2 cups cream 3 tablespoons sherry 1/2 cup fine bread crumbs 1 tablespoon butter

Melt the butter; saute the onions in it until tender, then stir in the flour. With a wire whisk continue stirring and cooking until a dark brown roux is formed. Stir in the chicken stock. (This may be made with 1 1/2 bouillon cubes dissolved in hot water if you have no stock.) And the chopped celery and parsley. You will now have a thick brownish paste. Cover tightly and simmer over a low heat for 20 minutes, then stir in the sliced mushrooms and sweetbreads broken up into bite-size pieces, then the cream and sherry. Cook over the same low fire until thickened, about 5 minutes. Put the mixture in a greased baking dish. Sprinkle the bread crumbs over the top and dot with the tablespoon of butter. The dish may be made ahead to this point. Bake for 30 minutes at 350 degrees. If you have held the dish in the refrigerator, add 10 minutes to the baking time. Serve with a green vegetable, salad, and crispy hot bread.