IN THE LAST few years I have joined the smugglers -- not of drugs, not of liquor, not even I of foie gras, but of plain, all-purpose flour. Why should anyone want to bring flour to France, a land famed the world over for its bread? The quality of French flour is precisely the problem. American flour reacts quite differently, and many time-honored French recipes simply will not work in the U.S. unless proportions are adjusted. So a cookbook written in France for the U.S. market must be tested with typical U.S. ingredients.

Milled from hard wheat, American flour has a higher gluten content than soft-wheat French flour. It is ideal for pasta and yeast breads, but, because of its tendency to shrink when kneaded, it is tricky for making pastry. Through experiments at La Varenne cooking school, we've discovered that American flour absorbs approximately 20 percent more water than French flour, which means that for use in the U.S. we must increase the amount of liquid or decrease the amount of flour in our recipes. This solution works for all but the most delicate doughs, like puff pastry, which require a flour akin to French flour, best made in the States by mixing three parts all-purpose flour with one part cake flour. So cake flour, not to mention American specials like whole-wheat, rye and buckwheat flour, are all crammed into my suitcase.

Flour is by no means the only problematic ingredient, though it certainly is the most bulky to transport. For example, French gelatin comes in cellophane-like sheets, not in powder form, and it is weighed by the gram, not measured by the envelope. The French use only cake yeast, so all of our recipes have to be retested with American dried yeast, which has double the leavening power per gram of cake yeast. French chocolate is dark and bittersweet, whereas the chocolate sold in the U.S., particularly in the wake of the cocoa crisis, tends to be either unsweetened baking chocolate or sugary chocolate chips. The nearest U.S. equivalent, semi-sweet chocolate, is milled differently and contains less cocoa butter than French chocolate, thus giving different results. We have trouble, for instance, making shiny coatings and icings with U.S. semi-sweet chocolate. And, of course, the French have no molasses, corn syrup or maple syrup, and their brown sugar, which is rarely used in baking, is quite different from ours.

Dry ingredients are relatively easy to transport to France for recipe testing; perishable ingredients are another matter. When the French call for cream in a recipe, they usually mean cre me frai che, a thick, partially fermented cream which resembles American sour cream but, like heavy cream, can be whipped and boiled without separating. To determine which recipes can be made with American heavy cream, we use English sweet cream purchased from Marks and Spencer in our Paris kitchens. For recipes in which cre me frai che is an essential ingredient, we culture our own cre me frai che from sweet cream and buttermilk, a procedure I've used in the U.S., England, Australia and South Africa. (It does seem an irony to make cre me frai che in its native home of France.) In addition, the French version of cream cheese, fromage fraise, has a much finer curd than its nearest equivalent, American cottage cheese, so the latter must be sieved or pure'ed in the processor for use in a French recipe.

Many fish varieties are the same in France and the U.S., but some, like the grunter and the prehistoric-looking scorpion fish -- essential ingredients in a Marseilles bouillabaisse -- are not available in America. So I consulted colleagues in Boston and San Francisco to devise substitutions that would allow American cooks to produce an authentic-tasting bouillabaisse. Because most American shellfish is purchased in its frozen state, we first freeze our fresh scallops in Paris to see how they cook when thawed. Crayfish, a common and classical garnish for many French regional dishes, had us stymied for a while until we tried substituting shrimp. The adapted recipes are slightly different, and often even tastier. Fish stock, another cornerstone of French cooking, presents problems since fresh fish bones so important to a flavorful broth cannot be found in many areas of the U.S. Again, a suitcase import is the answer, as bottled clam juice mixed with an equal quantity of water gives an acceptable, if somewhat salty, version of fish stock.

American and French chickens are similar, but Cornish game hen pales beside squab, quail or pigeon, though for recipe-testing purposes they can be substituted. Duck is another matter, and our U.S. recipe testers have a terrible time with pan-cooked dishes because American ducks are so rich in subcutaneous fat. Also, no book of regional cooking would be complete without a recipe for canard rouennaise made from specially smothered ducks whose blood is used to thicken and enrich the sauce. Even if there were a market for smothered duck in this country, the SPCA would never allow the practice. Fortunately we found that pure'ed liver could be used to thicken the sauce, retaining the traditional flavor.

The French raise superlative veal but mediocre beef, while just the opposite is true in the U.S. Not only do meat cuts differ in the two countries, but American beef, more generously marbled than French beef, requires less cooking time than its French counterpart. Organ meats, like brains and kidneys, which are popular in France, are simply unacceptable to most Americans. Tough, salty French bacon requires blanching before it can be added to a dish, but if American bacon is blanched, in dishes like hot bacon salad or boeuf bourguignon, it loses its flavor completely. Marks and Spencer keep us supplied with English streaky bacon, which resembles the American. The hardest part is keeping it away from the school chefs, who have learned to love lean bacon while on tour in the U.S., and who pilfer our testing supplies for their own American-style breakfasts.

Even vegetable recipes have to be adapted for the U.S. -- French cucumbers are twice the size of American ones; French eggplants are long and slender, not large and round like those in the States. No one comes to France without falling in love with slender French haricots verts. To achieve a similar effect in American kitchens, beans must be cooked twice as long, or laboriously sliced in half lengthwise. Fruits, too, must be adjusted since varieties of apples, melons and pears are quite different on the two continents.

For the most part, our ingredient importation takes a one-way path from the U.S. to France. Last winter, however, I wanted to bring a special present to thank our American colleagues who helped test the recipes for "La Varenne's French Regional Cooking": fresh truffles. How could I smuggle truffles, with their heavenly, incomparable perfume, into the U.S.A.? The odor of a whole kilogram is, to say the least, pervasive. Concealing fresh truffles in a suitcase is a little like trying to hide the Eiffel Tower under an umbrella. My husband, Mark, had the perfect solution in his clothes closet. We packed the pungent fungi in mothballs. Imagine my chagrin when, weeks later, I discovered that fresh truffles are not banned by the Customs Service after all!