AT ROUGHLY $200 a pound, the black truffle of France is one of the most expensive foods in the world. Used in sauces, salads, and as decoration in the highest haute cuisine, available fresh for a mere three months out of the year, these subterranean fungi are delightful to taste, and very difficult to find. The French employ trained pigs to sniff the black truffles from around the roots of trees. The Italian "whites" are equally elusive, and even more expensive. Hounds are used to scout their location.

Of course anything as rare and valuable as truffles is going to be the subject of imitation - even intrigue. According to gastronomic expert Robert McDaniel there has been a search for truffle substitutes at least since the time of Catherine de Medici. And though the genuine delicacy is widely imported here, records show that many chefs across the United States have responded to the high cost of truffles by using an imitation. Few have bothered to tell their customers.

The heart of the imitation truffle business is in Clinton, Maryland, where Johannes Jacobus Geldoff, a Dutch immigrant in his sixties, makes and distributes "Trufflettes." He's been at it for ten years. "It's a one-man operation," he says, "I do it all myself. I have a place where I make them and it's all hand work." He is reluctant to say more.

Despite repeated inquiries, Geldoff will not disclose the location of his operation, but one person who has dealt with him since the late 1960s and has been invited to watch the production process says, "He makes them out of his home - he lives over the place . . . He took the basement and turned it into a little factory."

Naturally there's no specific law against imitating truffles, but Geldoff's operation does appear to be illegal - whether or not he makes Trufflettes in his basement. If he does, he is in violation of the Prince George's County and State of Maryland regulations prohibiting people from making commercial food products in their home. In addition, a person must have both a "County Food and Drink Permit" and a "Use and Occupancy Permit" in order to manufacture food anywhere in Prince George's County; Geldoff has neither of these, according to county officials. Finally, Trufflettes are improperly labeled. The can says only "Pure Natural Ingredients" without saying what the ingredients are; the Food, Drug, and Cosmetic Act of 1938 requires that all ingredients be listed on the label.

Geldoff's product has apparently never been inspected by the county or the state. No one at the Maryland Food and Drug Administration, or at the County Health Department - including the area sanitarian in charge of Clinton - had any records concerning Trufflettes.

There is another imitation truffle on the market now, but it is hardly as successful as Geldoff's. Imported from Holland, the main problem with this imitationis that it tends to swell - instead of a delicate garnish, one gets black golf balls. Geldoff's product, at least, doesn't do that.

"Most of the difference between my product and the French truffle is the price," says Geldoff, and the cost is very different - five and a half ounces of real truffles are about $60 compared to $12.50 for the same amount of the imitation.

But real French truffles are nubbly, mushroom-like fungi with finely pocked skin. Their coloring is a rich black and their aroma is overwhelming - a distincitve combination that's spicy, garlicky, and a little like cheese. The smell of truffles, whether fresh or jarred, is so strong that they permeate any food with which they come in contact.

Trufflettes, on the other hand, have no aroma at all. Inside the can is a solid mass of black that looks something like tarred streets going soft on a hot summer day - all smooth and gooey.

Real truffles grow symbiotically with the roots of trees. On the other hand, Geldoff's product, as described in United States patent records filed in May 1967, consists of 70-75 per cent egg yolk, 10-15 per cent cornstarch, 10-15 per cent water, 1.5 per cent salt, and coloring. Theingredients are mixed, sealed, placed in hot water to cook and then cooled.

Trufflettes are sold in the Washington area by Geldoff himself. Atlantic Institutional Supplies of Alexandria, and the Watergate Restaurant Corporation.In addition Geldoff uses other distributors in New York City and New Orleans.

Though there is no indication that they're aware of the illegalities involved, many of those who market Trufflettes are reluctant to discuss their customers. "I sell to the big restaurants in town," says Geldoff. "There are a lot of French restaurants in Washington that use it, but I won't call any names because they use it on the menu as real truffles. They use Trufflettes for decoration and for sauce; in sauce they use real truffles too, mixed together. You can't tell the difference in a sauce, so why not?"

Stephen Gatti, general manager of Atlantic Institutional Supplies, is equally reluctant to discuss the names of his clients, but will say that the company, which has been marketing Trufflettes for six years, sells to between twelve and fifteen restaurants in the Washington area.

The Watergate Restaurant Corporation, which has sold Trufflettes since they first came out, distributes the product to restaurants across the country. Their invoices show that in Washington both Watergate restaurants - the Watergate Terrace and Les Champs - use Trufflettes, as do the Kennedy Center and the Marriott hotels. Elsewhere, they supply hotels, country clubs, and gourmet shops in Minneapolis, Detroit, Houston, Los Angeles, New Orleans, Boston, Chicago, Miami, Milwaukee, and New York.

The French Market in Georgetown is the only local gourment shop selling Trufflettes. According to a salesman they don't sell the product to private customers and they stock them only for the embassies. Which embassies? "Oh," he said as he started to laugh, "I can't tell you that - the chef doesn't want you to know that he put artificial truffles on his beautiful salmon."

It seems that socialities can now tell whether they're on the A or B list at parties by carefully examining the black flecks which garnish the platters, swim in the sauces, and glisten in the pate.

At the International Club, Maurice Bell says that he sometimes uses Trufflettes for decoration, but never for the sauce. "For the good buffet I always use the real truffle for decoration, but for the cheap party we use the imitation." According to Maurice at Ridgewell's Caterers, "We always cook the sauce with real truffles, but rarely use real truffles for decoration - if the customer asks for it we'll up the price. Like the party for King Hussein, we decorated with real truffles, but they don't care about the cost."

If the price of Truffles makes them too expensive to cook with, why don't chefs simply leave them out? The imitation is tasteless and has no aroma so it only adds color to a dish. And if the color black is essential for decoration, why not use black olives? "Because," says Claude Picard, the chef at the Madison Hotel who uses Trufflettes for decoration even though his prices rival the highest in town, "black olives aren't flat - you can't get the desired shape." Pulling out his set molds, Picard explained, "The imitation truffle is easy to work with and can be made just like you want it, any shape at all."

Two of the most respected French chefs in Washington are outraged by the widespread use of Trufflettes. Jean-Pierre Goyenvalle of Lion d'Or says, "You cannot reproduce a truffle with something that's like a ball of rubber." Jacques Blanc of Le Provencal echoes these sentiments and says, "Truffles play a tremendous role in French cooking and nothing can be used as a substitute. It's a question of trust - people have to trust us - the fact that you're not a chef and can't tell whether the truffles are real or not is not the point. Why not fill a bottle of Chivas Regal with cheap Scotch - it's the same thing."