What happens when a high school cooking class meets a French chef? Last week chef Jean Pierre Goyenvalle of Le Lion d'Or spent an hour with students at Charles Woodward High School in Rockville and the result was a range of questions, some serious, others amusing.

Goyenvalle left the stove of his downtown restaurant to fill in for James Beard, who was ill in New York. The original plan had been for Beard to discuss aspects of his new book, "James Beard's Theory and Practice of Good Cooking" (Knopf, $12.95), and in preparation the students had made recipes from that and other Beard books. But the discussion turned, quite logically, to some theories of French cooking and how they are practiced in restaurant kitchens.

Goyenvalle explained that in a relatively small restaurant such as his (110 seats) there is a team of four chefs plus himself for each lunch and dinner. They work at stations (broiler, fish, sauces and preparation), though they also take on other chores. In France, a similar restaurant would have probably twice as many in the kitchen because young apprentices are learning the craft, he said. "As a result sometimes here preparation has to be slightly different."

It also is somewhat easier to make elaborate dishes in a restaurant than a home, he explained; not just because professionals can work faster but because some of the basic preparations "already are done." To make a stock in which to poach a single chicken or fish takes the home cook considerable time. In a restaurant stocks are on hand.

Goyenvalle urged the novice cooks to "find one (cook) book in which the recipes are not too difficult to understand and the directions easy for you to follow. Don't jump from one book to another. Go to market, find something you like that's beautiful and fresh and just prepare it." French sauces, he explained, are often variations on one another. "Once you know the basics of it, French cooking is really very simple."

The salty onion soup had resulted, he told them, from adding salt before the stock was cooked down, thus the taste became concentrated with further cooking. "We never put salt in a stock pot," he said firmly.

The trick to achieving a bright shine and delicate extra flavor in a sauce was revealed, too. The chef simply whisks in a small nob of butter just before serving it. "After that you must not let the sauce boil," Goyenvalle warned, "or the butter will separate out."

His entree and dessert crepes are made from the same batter, partly because "in a restaurant you have to simplify so you can use your foods in many ways" and partly because "with sugar (as is recommended in many recipes for dessert crepes) it is harder to cook them properly. They become very brown." Goyenvalle suggested several filings, but what brought "ohhs" was his description of crepes filled with a souffle mixture and praline that is cooked in a hot oven for about 5 minutes.

As for making a souffle itself, a challenge some of the students had undertaken unsuccessfully. Goyenvalle said overcooking was a common error. That, he said, resulted in the batter becoming scrambled eggs. Another frequent mistake is overmixing the beaten whites into the base. The air bubbles are broken up and the souffle does not rise properly. Folding should be gentle but rapid, he said, suggesting the cook stir some of the whites into the base before folding to make it "sofe and easy to mix." Nor should the souffle be ignored during cooking. If there are hot spots in the oven, it may rise unevenly. if the oven temperature is not accurate, as frequently is the case, it may cook too fast.

The door may be opened and the souffle moved or the temperature adjusted. "Learn to work with your oven," Goyenvalle advised. "Put your hand into it. Feel the temperature." The audience responded to that bit of culinary wisdom with a few indvertant glances at hands and some nervous laughs.

They laughed, too, when Goyenvalle - after explaining that the French did not eat rich food and sauces all the time - told them "when I don't want to gain weight I don't eat much. It's the same solution in France as here."

"As chef are you ever satisfied with a peanut butter and jelly sandwich?" inquired a student as the conversation on diet continued.

"I've never tried one," responded the chef, thus clearly illustrating a basic difference between the eating habits of French and American children.

Goyenvalle promised to return soon to make a souffle with the students. His reward is likely to be a peanut butter and jelly sandwich.