IT takes a tough hillside to make a tender herb.

For centuries the finest sage, oregano, rosemary and thyme have been grown in the steep, rocky mountains of the Mediterranean. The dry, windy conditions are less than hospitable, but the stress on the plants fills their leaves with oil and results in more flavorful herbs.

Just down the hillsides, says B.H. Kaestner of the McCormick spice company, are whole villages deserted by residents searching for jobs in cities like Izmir (Turkey) and Athens. The tourist industry, he says, offers more economic possibilities than scouring the hills for scrubs of herbs. While herbs are still obtained from these markets, the dearth of labor causes their prices to climb.

Although imported-herb price hikes don't outstrip those of cars or Hershey bars, says Kaestner, the foreign picture probably won't get any brighter. As a result, companies like McCormick and Spice Islands are interested in joining the few extant domestic herb cultivators who grow herbs on a large scale. It's tough, however, to reproduce the flavor of the herbs that grow under those windy and barren Mediterranean conditions. The lush, agreeable California environment apparently produces pretty plants of dubious quality.

"It's like wine," says Thomas Burns, president of the American Spice Trade Association, comparing herbs to European grapes that are brought to California for wine production. "You take herbs and move them, and they change appreciably." Basil, dill, tarragon, marjoram (sometimes) and parsley have been cultivated in this country for many years. But it's difficult to reproduce the flavor of southern Europe-style sage, thyme, rosemary and oregano in areas where cultivation and harvest would be economically feasible.

Mexican oregano has replaced much of the Greek imports, according to Burns; half of the oregano imported here comes from Mexico. "Botanically, they're two entirely different products," he says, and the kinship of the Mexican to the Greek is not entirely clear. The Mexican herb is harsher and more biting, but it's appropriate for chili powders, Mexican foods and sometimes sausages. For many years, at least one company has sold Mexican oregano on the West Coast and Greek style on the East because of regional preferences. Now, since Mexican oregano is cheaper, says McCormick's Kaestner, some food processors substitute it for the Greek oregano.

Commercial herb growers and the government continue to experiment with herb cultivation. The research relies on manipulating the genetic heritage and the environment of the herbs. "This is a field we don't know much about," says Holly Shimizu, curator of the herb garden at the National Arboretum. "Cultivation of herbs in the United States is really quite new," relatively speaking.

So is the popularity of exotic herbs in the United States. Until World War II, sage was the last word in American herb preferences. Although imported spices were common in 1939, Americans relied very little on herbs from Southern Europe.

But American GIs returned from the war with a taste for ethnic foods, primarily pizza and spaghetti, and the popularity of herbs began to grow like a patch of parsley.

Since then, herb sales have grown in spurts, first one becoming popular and then another. Between 1940 and 1953 there was a "huge zoom" in oregano sales, a 1,400 percent increase in imports, says Marshall Neale, whose firm has handled public relations for the American Spice Trade Association since 1938. In the mid-'70s, there was a 20 percent jump, from 5 million to 6 million pounds. And one ounce of oregano can season 432 slices of pizza.

The darling of this decade appears to be basil, according to Department of Agriculture import figures, which show a threefold increase in imports from 1981 to 1982. The "battle for the spaghetti sauce market" is partly responsible for this, says McCormick's Kaestner. Overall, the preference for Italian food in this country is so pervasive, say the experts, that you can't even call it ethnic food any more. That, coupled with what Kaestner calls the "Mexican food explosion," accounts for the 3,748 metric tons of oregano and the 1,119 metric tons of basil imported last year, and the increasing popularity of the coriander leaves (cilantro or Chinese parsley).

Recent dietary changes have created another type of revolution in flavor, says Marshall Neale. Cooks are learning to rely on herbs for flavor rather than fat and salt. And the interest in ethnic foods put more focus on herbs.

Industry accounts for more than 60 percent of the revolution, according to Neale. Food manufacturers who "are searching for flavor when they cut down on calories and rich ingredients" tend to rely on herbs, he says. Since salt is increasingly frowned upon, food manufacturers turn to herbs to improve the palatability of their products. Thomas Burns says that working women use herbs to improve processed foods they rely on for meals.

There's no way to measure domestic herb production in the United States. Herb cultivator Alois Pastor won't divulge exactly how much basil, dill and tarragon he grows on his 300-acre herb farm in San Jacinto, Calif. He's one of a very few commercial growers, and he sells to a specialized market where looks are as important as flavor. Pastor, who's been growing herbs since 1949, says that although he is constantly experimenting with herb growing, there's no way he can match imported sage and other herbs. And the specialists agree that Americans will depend on the European herb supply for a long time to come.

Just like wine grapes, herbs will grow in nearly any temperate climate. It was the European herbs, however, like the European wines, that set flavor precedence, and it is those flavors and flavor concentrations that consumers prefer, at least for now.

But just as regional vintners prefer their own wines to their more famous counterparts, American gardeners find their own herbs, fresh and dried, far preferable to dried ones imported from Greece, Turkey or the south of France.

No matter where they come from, herbs are meant to enhance the foods we eat. As Waverly Root said, "Wheat and beef, rice and fish are the prose of food, herbs and spice are its poetry." GRILLED LEMON CHICKEN WITH OREGANO (4 servings) 2 pounds boneless chicken breasts, cubed 3/4 pound mushrooms, halved For the marinade: 1/2 cup white wine 1/3 cup lemon juice 1/4 cup vegetable oil 1 1/2 teaspoons oregano 2 cloves garlic, minced

Place chicken and mushrooms in a shallow baking dish. To prepare marinade, place wine, lemon juice, oil, oregano and garlic in a container with a lid and shake to combine. Pour marinade over chicken and mushrooms and refrigerate for 2 hours.

Skewer chicken and mushrooms on four skewers, alternating 3 pieces of chicken with a mushroom half. Broil for 10 to 15 minutes, turning once or twice. Serve with rice. LAMB STEW WITH MARJORAM (4 to 6 servings) 3 pounds lamb shoulder, cut into 1 1/2-inch chunks 1 large grated onion 1 teaspoon freshly ground black pepper Salt to taste 2 garlic cloves, minced 5 tablespoons chopped parsley 2 1/2 pounds zucchini, sliced 1/2-inch thick 2 teaspoons marjoram

Trim and discard excess fat from the lamb. Brown meat in a large dutch oven. Add onion, pepper, salt, garlic and parsley. Add 2 cups water, cover and simmer until tender, about 30 minutes. Remove meat from the casserole and place in baking dish. Degrease the sauce, if necessary. Add sliced zucchini and marjoram and cook 10 minutes. Place it on top of meat. If necessary, thicken the sauce by boiling it down. Pour over the meat and reheat in a 400-degree oven. Serve hot. TARRAGON POTATOES (6 servings) 2 pounds potatoes 2 cups milk 1 teaspoon fresh tarragon or 1/4 teaspoon dried Nutmeg 1 teaspoon salt 1/2 teaspoon freshly ground pepper Butter

Slice potatoes without peeling and place in baking dish. Pour milk over potatoes. Sprinkle with tarragon, a little nutmeg, salt and pepper. Cover and bake at 375 degrees 30 minutes. Remove cover, dot potatoes with butter and bake, uncovered another 40 minutes. PIZZA CACCIA NANZA (1 round loaf)

2 1/2 cups flour

1/2 teaspoon salt

3/4 teaspoon active dry yeast

1 cup warm water

2 cloves garlic, slivered

2 tablespoons rosemary

3 tablespoons olive oil

Salt and freshly ground black pepper to taste

Combine flour, salt, yeast and water in a mixing bowl. Blend well, then turn the dough onto a lightly floured board. Knead well, for about 15 minutes, and shape the dough into a ball. Place it in a lightly greased mixing bowl. Cover with a towel and let rise in a warm place until doubled in size, about an hour.

Turn the dough onto the board and knead once more. Put it back into the bowl and let rise again. Then punch down the dough and turn it onto a lightly floured board. Roll it out to 1/2-inch thickness. Rub the surface of a baking sheet with oil. Transfer the round of dough to a baking sheet. Make indentations over the surface of the dough and insert a thin sliver of garlic and a bit of rosemary into each indentation. Pour the olive oil over the pizza and rub gently with the hands. Sprinkle with salt and pepper and bake 15 minutes or until golden brown. Brush the garlic away before serving. From "Italian Family Cooking." HERBED SHRIMP SAUTE (4 servings) 1/4 cup good quality olive oil 3 tablespoons finely minced shallots 4 large cloves garlic, minced 1/2 cup minced fresh parsley 1 pound canned plum tomatoes, drained with liquid reserved Freshly ground pepper and salt to taste 1 teaspoon dried thyme 1/2 teaspoon dried oregano 1/4 teaspoon hot red pepper flakes 1 pound fresh shrimp 2 small zucchini, trimmed and chopped Rice for serving

Heat 2 tablespoons olive oil in skillet. Add shallots, garlic and half the parsley, stirring over medium heat until softened. Chop tomatoes and add them to shallots along with pepper, salt, thyme, oregano and hot red pepper flakes. Cover and simmer 20 minutes. Meanwhile, heat remaining oil in another skillet. Add shrimp, being careful not to overlap, and stir them over high heat until they just begin to turn pink. Remove from skillet and set aside. Add zucchini chunks and stir over medium-high heat until they begin to brown. Add shrimp and zucchini to tomatoes and cook, uncovered, 3 or 4 minutes. Serve over rice sprinkled with remaining parsley.

Note: Add water to tomato liquid and use for cooking rice.