Thought about prunes lately? Probably not in polite company. There is, however, a campaign by the California Prune Board to bring the prune out of jokes and into the American diet.

The first stage of the campaign tried to sophisticate the prune. Stressing that many great French chefs highlighted prunes frequently in their dishes, it included a sweepstakes to raffle off a gourmet dining tour of France. And while it is true that the French delight in prunes and it is not uncommon in southwest France for grateful guests to present their hostess with a beautifully wrapped box of prunes, the Americans didn't buy the idea or the prunes.

So the firm went after the truly marketable elements -- nutrition and health. "We are now positioning it as the high-fiber fruit," says Gavin Goodrich, of Oglivy & Mather in San Francisco, an advertising agency hired to uplift sales of prunes. "Prunes have one of the highest fiber contents among all fruits."

Susan Mesick of Ketchum Public Relations, hired by the California Prune Board, said that after the campaign of sophistication, sales of prunes "remained pretty much flat last year." She continued, "This campaign is more in keeping with the current trends of health. We are concentrating on the fact that not only do they contain fiber but that they are good tasting, too."

No joke, prunes are one of the richest sources of dietary fiber. Two ounces of dried prunes (or 6 prunes) have 9.2 grams dietary fiber, compared with 1/3 cup of bran cereal with 8.9 grams, an apple with 3.0 grams and 1 regular slice of wheat bread with 2.1 grams. They contain both sorts of dietary fiber (soluble and insoluble), lignin, cellulose and hemicellulose, which are insoluable and have a water-holding capacity, thus preventing constipation, and pectin, which is soluble and aids in gel formation and is a cholesterol-binding agent. As all fruits, prunes have no cholesterol; and they are rich in potassium, iron and vitamin A.

Easily incorporated into meals, prunes can be added to breads, muffins, cookies and pancake batter for rich flavor and improved moisture. Breakfast is the most convenient meal to sneak in a few prunes; chop them over cereals, combine them with fruit juices or cook them in simmering water for a warm snack of extra-plump prunes.

The French were right to use prunes in their dishes, thus blending the deep rich and sweet flavor with pork and chicken to create exotic tastes. The dish below was adapted from a recipe in Jane Grigson's Fruit Book (Atheneum, 1982); in the interest of lowering fat consumption, the cream has been omitted, but the dish is nevertheless delicious. If you already have flour, butter, salt and pepper in your home, this will require only a short stop at the express lane.

EXPRESS LANE: prunes, white wine, pork tenderloins, oregano, red currant jelly, lemon juice PORK WITH PRUNE SAUCE (6 to 8 servings)

1 pound pitted prunes

2 cups medium-dry white wine

3 pounds pork tenderloin

1 cup flour mixed with 1 tablespoon oregano and salt and pepper to taste

2 tablespoons butter

1 tablespoon red currant jelly

Salt and pepper to taste

Parsley for garnish

Bring prunes to a boil in the wine and simmer for 10 minutes.

Trim the tenderloins and cut them diagonally into thick slices just under 1/2 inch. Turn them in flour and fry them quickly in butter until they are nicely browned on both sides. Pour in the prune juice and simmer a few moments until they are cooked through. Transfer to a serving dish, arrange the prunes around them and keep warm. Add jelly to pan juices, whisk and boil down to concentrate the flavor (this will depend on the quantity of prune juice); it should be a delicious syrupy essence. Season to taste. Pour over the pork, and scatter with a small amount of chopped parsley. Serve very hot.