FARMERS IN Prince George's County mind their peas and corn.

So much so that when they plant these vegetables each spring, they use the Heat Unit Theory (HUT) to plan harvesting and can estimate within a week when the crops will be ready for market.

It's a backwards technique that's been around for a good 20 years, says David Conrad, an extension agent at the Prince George's County Cooperative Extension Service. First, farmers determine what week they want to harvest their crops, then they determine when to plant them according to how many good growing days are both needed and expected during the spring growing season.

They do their planning according to daily average temperatures for the area, keeping in mind the optimal temperatures at which peas and corn grow fastest.

Peas, says Conrad, grow best between 40 and 75 degrees within 60 to 70 days. Days with temperatures that fall within this range are called heat units or growing degree days. The number of degrees that the temperature rises above 40 on any given day determines the speed with which the plant will grow. "Simply, the higher the temperature, the faster the growth rate," Conrad says. "It's really no different with growing tomatoes; the figures simply haven't been worked out for this area as of yet," says Conrad.

Below 40 degrees, he explains, pea plants become dormant and stop growing. When the temperature rises above 75 degrees the plants' growth will also be slowed. Under normal conditions the peas have reached their "physiological maturity" by the end of May and must be harvested before the plant dies off.

Other spring and summer vegetables are planted "whenever field conditions are right and the planting season has arrived. It's based on a gut feeling," Conrad says. Farmers can estimate crop maturity of these vegetables only within a range of two or three weeks.

Like all crops, though, Prince George's County peas are appearing late in the market due to an unusually cold, wet spring. This doesn't mean the HUT theory doesn't work; it's because "we haven't experienced the growing degree units that we normally experience in the spring," Conrad says.

Although pea lovers have had to wait an extra three weeks, the tiny bright green seeds within a pod are flooding the markets. Peas squeak to let you know they are perfect. While the technique takes a little practice, squeeze a pod between your fingers and rub the peas against one another. If they squeak, you know they're going to taste great. Avoid light-colored, swollen pods as they will be tough and mealy. Wrinkled skins are a sign that the peas have passed their peak and have lost some flavor.

Peas, like corn, are best when taken straight from the garden to the table, braised quickly in a bit of water and seasoned with salt, pepper and butter. Sadly, though, for every pound of peas you get just a cupful for the table, and that's a lot of podding for each single serving.

The Maltese Scampi recipe that follows is one way to spread the beauty and flavor of garden-fresh peas without burying their wealth with other ingredients. Peas and Cucumbers in Sour Cream tastes wonderful cold or hot and is a colorful side dish for grilled meats. Curried Peas and Potatoes is an Indian recipe that won't require a trip to a specialty market for the ingredients. You can buy ground cumin and coriander at any grocery store.

Be sure to shell the peas just before cooking to retain freshness and nutrients. They are rich in Vitamins A and C and iron and have traces of riboflavin, thiamin and niacin. Fresh peas may be stored in their pods in the refrigerator for two or three days. MALTESE SCAMPI (6 servings) 1 1/2 to 2 pounds large raw shrimp For shrimp marinade: 1/2 cup olive oil 1/2 cup vegetable oil 1/3 cup lemon juice 2 tablespoons tomato paste 1/4 cup chopped parsley 1 tablespoon dried oregano 1/2 teaspoon salt 2 tablespoons chopped garlic 1/2 teaspoon hot pepper sauce For scampi: 1/4 pound smoked sausage (kielbasa or chorizo) 1 to 1 1/2 pounds peas 1/2 pound scallops 1 pound mussels 6 tablespoons butter

Peel and devein shrimp.

Whisk the marinade ingredients together. Pour over shrimp and marinate in the refrigerator for at least 3 hours.

Prick sausage with a fork; blanch in boiling water for 5 minutes to release fat. Cool, slice diagonally in 1/4-inch pieces and set aside. Shell peas, blanch for 1 minute and cool; set aside. Wash and scrub mussels, removing beards.

When you are ready to cook, remove shrimp from marinade, heat butter and saute' shrimp over high heat until pink on one side (about 1 minute). Shake the pan occasionally. Turn shrimp; add scallops, sausage and mussels. Saute' 2 to 3 minutes longer, or until the shrimp, scallops and sausage are lightly browned and the mussels have opened. Add the blanched peas during the last minute of cooking. From "The Victory Garden Cookbook," by Marian Morash PEAS AND CUCUMBERS IN SOUR CREAM (6 servings) 3 cups freshly shelled peas (about 3 pounds of pods) 2 medium cucumbers 1 cup sour cream at room temperature 3 tablespoons finely chopped fresh dill Salt and pepper to taste

Cook the peas in boiling salted water until barely tender (about 1 minute). Drain. Peel the cucumber, quarter it and scoop out the seeds, then dice it. Cook the diced cucumber quickly for about 2 minutes in just enough boiling water to cover. Do not overcook as the cucumber should remain crisp. Drain immediately. Just before serving combine the cooked cucumber and peas in the top of a double boiler, then mix in the sour cream, dill and salt and pepper to taste. Heat slowly over hot--not boiling--water until the vegetables are warm. Serve. From "The Four-Season Cookbook," by Barbara R. Fried CURRIED PEAS AND POTATOES (6 servings) 2 tablespoons vegetable oil 1 large onion, sliced 1 teaspoon ground cumin 1 teaspoon ground coriander 1 teaspoon turmeric 1 serrano or jalapeno chili pepper, seeded and minced (or to taste) 1/2 teaspoon freshly ground black pepper 1/2 teaspoon salt 2 pounds red new potatoes (about 3 large), boiled and cubed 1 cup green peas

Heat oil over high heat in large skillet. Add onions and brown over medium high heat. Add cumin, coriander, turmeric, jalapeno, black pepper and salt and stir for 1 minute. Add potatoes (peeled, if preferred), peas and a little water. Cover and steam until peas are cooked through--if frozen 5 or 10 minutes, if fresh 2 minutes.