Finding the freshest food at open-air farmers markets

''Don't poke the merchandise when you shop at a farmer's market this summer. It's hard not to, but you really won't be able to tell much,'' according to Fran Garvan, who has written a book about the open air food stands now appearing in large cities during summer months.

''Scout out the whole market before you buy. Get to know a few vendors and don't hesitate to ask how to coo- something or where it comes from,'' she advises.

''Discuss prices but don't bargain. If you expect rock-bottom prices, you're likely to get rock-bottom quality and service.

''And don't expect to find super bargains at the end of the day. Consider if it's worth a few pennies to have food that sat in the sun all day,'' she says.

Fran Jurga Garven, who grew up on a New England farm and has had experience in the restaurant business in United States and Canada, knows about many kinds0 of farmers markets.

''A fArmers market'' she explains, ''can be anything from a group of local gardeners selling their extra outdoor zucchini out of the back of station wagons , to a huge indoor arena of food sellers and dealers that attracts thousands of customers a day.

''No matter what size farmers markets are, and whether they're in the city or the country, acceptance by the public seems to be universal. People like to shop at them and will if they have time and access,'' she says.

Her book, ''The Farmers Market Cookbook'' (Harvard Common Press, Harvard, Mass., $14.95; paperback, $8.95) is sectioneL into monthly chapters highlighting the current harvest with re#ipes and buying information.

Whether you're thinking of selling your own produce or just want the best value for your grocery money, you'll find tips from these monthly guides.

The chapter on the month of May, for example, features everything you ever wanted to know about fiddleheads - and more - as well as timely recipes for dandelion greens and strawberries with rhubarb.

Also in order are tips for savoring zucchini, cukes, tomatoes, and corn during summer months.

June continues with a menu including several easy dishes cooked in Chinese style - Stir-Fried Broccoli and Mushrooms, Shrimp, and Broccoli in Sesame Sauce, two recipes for bluefish and a strawberry cheesecake recipe.

In November, she tells how to roast a turkey until ''you wiggle a drumstick and it falls off in your hand'' - which I would consider overcooked.

The turkey is in a definitely nontraditional, if not strange, menu of curried corn pudding, baked eggs Florentine, whole-vegetable tempura, and Jerusalem artichokes with pignoli nuts! Oh well, to each his own.

''Your Christmas Goose,'' a gingerbread house, and sculpture dough, are December offerings, and January's advice is well taken - a New Year's resolution ''to organize your food system once and for all.''

The author is assuming you have a well-stocked kitchen, as well as many friends who drop in to eat on unexpected evenings or long after stores are closed.

''After all,'' she says, ''the best place to start organizing your social life is right in the middle of your kitchen, so now might be a good time to evaluate both your social and your cooking lives.''

While the selection, storage, and use tips are helpful, the coverage of certain items in various months defies logic. And some of the choices, notably bananas, would never see the light of day at a bona fide local farmers market in the continental U.S.

She does explain, however, that ''France has strict controls on imported food , particularly fresh produce. . . open-air markets are fiercely preserved'' and local farmers ''encouraged to keep up their growing and selling cycles.''

The book is attractively illustrated and well designed, and most cookbook fans are bound to find something to please tucked away in its 130-odd pages.

Here are recipes from the book, to please both friends and family. Marinated Carrots, Broccoli, and Cauliflower 1 small cauliflower, broken into tiny flowers 1 head broccoli, in flowerets 2 pounds of carrots, sliced 2 small onions, diced Several sprigs of fresh parsley Marinade: 1/2 cup sugar 1/2 cup white wine vinegar 1/2 cup olive oil 1/4 cup lemon juice

Combine marinade ingredients except lemon juice and bring to a boil; then remove from heat. Add lemon juice and stir well.

In a large glass jar or salad bowl, arrange vegetables in layers by colors. Use a thin layer of onions between broccoli and carrots.

Stud cauliflower and carrot layers with parsley sprigs that are visible from the outside. Pour marinade over all and cover.

Marinate at room temperature or in a refrigerator at least 8 hours before serving. Have pepper mill on the table for seasoning. Baked Haddock in Sour Cream and Dill 2 pounds fresh or frozen (thawed) haddock 2 cups sour cream 1/2 cup mayonnaise

1 teaspoon celery salt 1/2 teaspoon pepper 1/4 teaspoon thyme 1/2 teaspoon paprika Enough fresh dill to cover or 1 tablespoon dried dill Sliced lemon Parsley for garnish

Wipe fish dry with paper towels - do not wash it. Lay it skin side down, in a greased, shallow baking pan. Preheat oven to 350 degrees F.

Mix together sour cream, mayonnaise, celery salt, pepper, thyme, and paprika, and pour over fish. Use a spatula to spread sauce evenly. Cover with fresh dill, or sprinkle liberally with dillweed.

Bake 40 minutes or until fish flakes easily. Serve with parsley garnish and a slice of lemon. French Fries Deluxe 4 large potatoes Flour 1 beaten egg 1/4 cup milk Vegetable oil

Wash potatoes and remove any eyes or sprouts. Cut into cubes, slices, or French fry sticks. Dip into flour, then into egg mixture. Fry in about an inch of oil until brown and crisp. Drain and blot dry. Applesauce Cake 1 1/2 cups brown sugar, packed 1 cup butter 2 eggs 2 teaspoons baking soda 2 cups thick unsweetened applesauce 3 cups flour 1/2 teaspoon salt 1 teaspoon ground cloves 2 teaspoons cinnamon 1/4 teaspoon ground ginger 3/4 cups chopped nuts Cream butter and sugar. Add eggs and beat well.

Sift together flour and spices. Gradually blend into creamed mixture. Mix baking soda into applesauce and add to batter. Pour into greased and floured 9 -by-13-inch pan and bake at 350 degrees F. 50 to 60 minutes. When cake is cooled , frost with penuche frosting. Penuche Frosting 2 cups light brown sugar, packed$ %/2 cup milk 1/2 cup butter 1/4 teaspoon salt

Mix ingredients together in heavy saucepan. Stir over low heat to melt sugar, then bring to a full boil, stirring constantly.

Boil exactly 1 minute. Remove from heat and beat until lukewarm or of spreading consistency.

Janet Christensen is former food editor of the Boston Herald-Traveler and is now home economist at the Massachusetts Department of Agriculture.