If it's a tenet of European wine making that the grapes of a great wine must be grown in sight of a river, it should likewise be a tenet of American restaurant going that no great restaurant can exist in sight of the ocean - particularly, if the restaurant is in a beach resort.

One man who is working to disprove this statement is John McDonald. McDonald, 36, is one of three proprietors - and the head chef - of The Garden, a small restaurant in Ocean City, Md., on Route 1, the Coastal Highway.

It is located just 50 yards from the ocean and not much further from the Delaware line in a primarily residental area, north of the gas stations, fast-food places and high-rise condominiums that are generally associated with Ocean City. Featuring a discrete mixture of classic French dishes with some recipes direct from Larousse Gastronomique, adapations of French and Italian dishes and a number of his own inventions. The Garden is in the middle of its third highly successful year.

Classic dishes include Flounder Meuniere Orange and Crabmeat Remick; adaptions include Veal Romana, with a Finnish Swiss-type cheese and Polish Ham substituted for Fontina and Proscuitto; and inventions include Crabmeat en Chemise and Shrimp and Lobster Marsala. These are also the restaurant's most popular dishes. Aside from shrimp, just about all the food used or served by The Garden is fresh. Vegetables, such as acorn squash and carrots, are locally grown.

After opening or managing popular, though less food-oriented, place in Ocean City, including the Quarter Deck and the Sheraton, McDonald accepted the position of food and beverage director with a large hotel company in Kansas City, Mo. What he thought would be the pinnacle of his career turned out to be a big disappointment. "I was particularly upset at the way the company treated its employes," he explained. "I decided I'd rather be my own boss and do things my way."

One night McDonald and two old friends, Jim Lennon, who had accompanied him to Kansas City, and George Parrott, who was living in Ocean City but vacationing in Kansas City, were reminiscing about the Eastern Shore. The Garden was conceived. McDondal and Lennon promptly quit their jobs and the three returned to Ocean City. A few months later, The Garden was born.

In appearance, the restaurant is solidly California-style, with plenty of wood and green plants. There are also Tiffany lamps, cut-glass originals and a few off-beat pieces of furniture, such as an apothecary display case by which the host - frequently McDonald - stands and greets guests when he is not in the kitchen. Many of the 98 diners The Garden can accommodate sit on church pews, actually quite comfortable when one is eating well. Attractive photographs grace the walls.

There were few changes made in food or personnel, once the restaurant got off the ground. The staff, experienced and happy, according to McDonald, has remained intact. One improvement, however, was in the desserts. Rita Anderson, a friend of the proprietors and head cocktail waitress at the Sheraton, expressed displeasure one day at the selection. She was promptly made dessert chef, baking walnut cake with a pistachio cream icing, Harvey Wallbanger cake and Rita's Delight (a white pound cake with vanilla custard filling and a coconut and pineapple frosting) in her off hours. This year she quit the Sheraton to work full time at The Garden.

The propietors are justly proud of their wine list, where most of the items are marked up just 40 percent from retail. A 1976 Berncastler Auslese sells for $7 while a '76 Grand Cru Chablis (Les Clos) sells for $10.50

One of the reasons for the success of The Garden is that it is small. "Once a place gets much over 100, it is hard to maintain quality," McDonald says. That also explains why the restaurant has had no imitators.

Why are there so few good restaurants in ocean resorts? McDonald believes that most people do not want to eat big or heavy meals there and restauranteurs assume that they won't frequent a good restaurant. "A restaurant will do well if it serves good, fresh and light food, emphasizing fish and veal rather than beef or lamb," McDonald says. "We do and we have," he adds.

Surprisingly, two-thirds of the restaurant's clientele is local - only one-third comes from Washington or Baltimore.

The Garden is open from April through October, seven nights a week, from 5:30 to 11:30 p.m. Dinners, which include a main course, salad, two vegetables, a potato and fresh fruit, run between $9.50 and $13.50. FLOUNDER MEUNIERE ORANGE

(4 servings) 2 pounds fillets of flounder (or fluke or rockfish) 4 tablespoons clarified butter (see Notes) 4 tablespoon flour 2 eggs, beaten 2 ounces orange liqueur 2 or 3 ounces orange juice 2 tablespoons chopped parsley

Dredge fillets in the flour, shaking off excess. Pass fillets through beaten eggs, making sure to cover but not to soak the fillets.

Meanwhile, in frying pan large enough to hold the fillets in one layer, heat 2 tablespoons of butter over medium heat until butter just begins to brown. Place fillets in frying pan. When brown, turn. Fish should be slightly underdone. Remove fillets to heated dish or place inside oven which has been warmed to 200 or 225 degrees. Add remaining butter to pan and heat until sizzling. Add orange liqueur and heat; then ignite. When flame has extinguished, add orange juice. Increase heat and cook 2 to 3 minutes. Remove sauce from heat, add chopped parsley, and pour over fish. Serve immediately.