FRENCH FRIES did not become French very easily. As a matter of fact, potatoes - natives of the New World - were introduced to Europe by Spanish explorers around 1550. They became popular in Spain, England and Italy. But at the beginning of the 18th century, the French still were turning their noses up at them.

Then along came Antoine Auguse Parmentier, an economist, agronomist and public relations expert who believed that potatoes were a necessary food for the people of France, since the country was immersed in a horrible famine.

As the story goes, Parmentier had a group of palace guards stationed around a potato field 24 hours a day. After a while, curiosity built to the point where the public wanted to know what this important piece of real estate was all about. It was enough of a gimmick to get the French to try potatoes, and they have been eating them ever since. In fact, they managed to develop a style of cutting and cooking them that is known as "french fries" everywhere but in France itself.

No matter how you slice it, french fries are the vegetable cornerstone of the fast-food industry. A hamburger on a plate looks naked without them. Unfortunately, all too often a grease-sodden group of limp sticks masquerades as this dish fit for a king. (Louis XIV loved his pommes frites.)

The "real" french fries are twice-fried, an easy dish to prepare at home, and certainly worth the effort. Here are some tips:

Almost any variety of potato may be used, and the more mature the better. Many professional cooks think Idahos produce the best results because of their shape and high starch content. The potatoes may be peeled, but for extra vitamin retention, well-scrubbed skin may be left on. The potatoes should be uniformly cut with the grain into 1/4-inch to 1/2-inch slices. The slices should be soaked in cold water for at least 15 minutes, and then thoroughly dried on paper towels to remove moisture and excess starch.

Any deep, heavy pot or saucepan may be used for frying. The container should not be more than half full of fat, oil or shortening. If you plan to do a lot of frying, a deep-fat thermometer and a wire basket are excellent investments.

The first frying operation is to blanch the fries. They should be placed in small batches into fat that has been heated to 275 degrees. Be careful not to heat the fat so that it smokes. In order to test without a thermometer, place one slice of potato in the hot fat and cook until it looks creamy and all sputtering has stopped. Remove from fat. It should mash easily with a fork.

Once in the fat, they should be free to move easily. Remove and drain on paper towels. Skim fat after each frying to remove any crumbs. Allow fat to reheat to 275 degrees and repeat. This step may be done well ahead of serving time.

The second frying, or crisping phase, must be done just before serving. The fat should be heated to between 350 and 375 degrees. To test, use a deep-fat thermometer or place a 1-inch square of white bread in the fat. It should brown in about 40 seconds. Cook potatoes in small batches until golden brown. Remember to skim the crumbs off the fat after each frying. Drain on paper towels and salt to taste. Serve while still hot.

The fat may be reused. When slightly cooled, strain to remove any left over particles. Store in a cool place in a covered container. When the fat becomes thick and dark, discard it.