After two years of trial and error, Michel Guerard is coming out of the deep freeze. The sprightly, witty, inventive Prince of Nouvelle Cuisine and King of Cuisine Minceur is about to rock the gastronomic world again.

On April 17, the first of a series of Guerrddesigned frozen dishes and forzen sauces, manufactured by Findus, went on sale in 30 Paris supermarkets and specialty grocers.

Early in the month the sharpest tongues of the French press gathered for a sampling aboard the river restaurant Lefebvre, moored near the Eiffel Tower. The four initial cooked dishes were presented in between Guerard-labelchampagne and Guerard-label armagnac:

Terrin ede rascasse du Nord, supposedly a North Atlantic cousin of the Mediterranean rascasse used in bouillabaisse. A medallion of fish mousse, pale ivory perked up with specks of carrots and green peas, served warm in a sea of watercress sauce. Visual appearance: excellent. The mousse: too bland for this crowd, bored with the baby-food texture that has been fashionable the last few years. Unanimity on the full-bodied sauce - a happy color of spring and the taste of cress fresh and strong - and a clamor for it to be marketed on its own.

Filets de merlan (whiting) napped with a julienne of vegetables, discreetly saffroned. A for effort. The look corresponds to that of dishes in modish Paris restaurants. The slivers of vegetable maintain their individuality. Main carp: Turbot would have been nicer than whiting, but big business demands obeisance to budget.

Terrine chaude de volaille, sauce auxcepes et au girolles. This was more like it. Real bites of diced chicken and vegetable in the light chicken mousse. Aroma of forest mushrooms, miraculously intact. A hint of armagnac in the sauce. Everybody seemed to forget that the stylish littlt hors d'oeuvre had been kept on ice six months before being dropped, still in its plastic sack, into a pot of boiling water.

Fricasee de poulet au vinaigre et au poivre vert. Good-sized chucks of chicken had been gently browned before being cooked in a reduction of robust red wine and fine vinegars and aromatized with green peppercorns. Oven heating is required to bring it back to life from its frozen state. The style of the dish is regional with a Guerard twist on the traditional. Reactions were mixed and rabidly partisan. My hand went up in favor.

Fresh noodles were served to sop up the "old-fashioned" sauce. This is the kind of dish that is reassuring to the French," Guerard said. "We will be moving more in this direction."

Guerard's involvement with freezing on an industrial scale happened at a small lunch at the three-star Paris restaurant Taillevent in spring of 1976. Among the guests was Pierre Liottard-Vogt, president of Nestle, the parent company of Findus.

Would Guerard care to try his hand at cooking for the cold wave that inevitably is part of France's future? queried Liottard-Vogt.

Guerard curious and creative about all aspects of kitchen chemistry, is smart enough to leave business to a businessman. His commercial mentor is Claude Jolly, a former textile executive with a Walter Mitty steak who under the name of Claude Lebey writes the food column for the French weekly newsmagazine L'Express. Jolly auctioned the U.S. right to Guerard's book "Cuisine Minceur" for $100,000 to William Morrow and developed Guerard's Comptoir Gourmand, a gastronomic boutique whose pilot shop on Place de la Madeleine in Paris will soon be expanded into a chain.

With Findus, he negotiated a contract which has made his protege the most rewarded chef in France, and certainly the most envied. The U.S firm that bid double was turned down, for fear that the Guerard name would be cashed in on without enough say in the final product. (However, since Nestle controls Stouffer's in the United States, Guerard dishes eventually may land on American TV lap trays.)

Since October 1976, a Findus brigade of chefs and a team of research technicians have been making monthly descents upon Guerard's gourmet retreat in southwest France. Every fortnight in between, Guerard has been traveling north to the Findus labs in Beauvais.

"I soon learned I knew almost nothing about freezing," Guerard said in his office behind the Comptoir Gourmand.

Cooked dishes offered problems and surprises. A cooked dish when frozen undergoes alternations for six months, after which it is stabilized for the next year and a half to two. He gave a resume of some of the unexpected things he met.

Oily fish such as salmon or mackerel and fatty meats such as certain types of pork and duck develop a rancid taste. Fresh herbs taste dried or rotten and also lose their subtlety unless specially treated according to the imposed conditions. Lyophilization did not help. The solution was to infuse them in oil.

The whiting in the Merlan a la julienne de legumes in the first months of experimentation gave off water, which made the sauce too fluid. The celery in the julienne absorbed the salt of the fish and became inedible until it was cooked in butter separately before being tossed with the other vegetables.

Citrus fruits have a tendency to degenerate, producing a taste like ether.

Of 40 Guerard recipes, Findus has retained 25 for further development. A hollandaise is almost ready and a cheese souffle is still under testing. In marketing tests, peasant dishes are proving more popular than nouvelle cuisine. A cassoulet is on the agenda. Guerard is particularly fond of a southwest daube des bonnes femmes , a longsimmered stew of pork, lamb, cabbage, white beans ant tomatoes.

There are high hopes for a bouillabaisse of morue (cod), a recipe which brought great response from viewers of Guerard's fortnightly television program.

The dishes that go on sale in a few weeks are priced at 20 to 24 francs (about $5 and $6) in packets whose portions will serve two and include a plastic sachet of sauce. Sauces when sold apart are priced at 8 francs. CAPTION: Picture, Michel Geurard by Dan Wynn for The Washington Post