"Valentine, Saint (d. 3rd century, Rome), name of two legendary martyrs whose lives seem to be historically based and who are commemorated on Feb. 14 . . . . St. Valentine's Day as a lovers' festival and the modern tradition of sending Valentines cards have no relation to the saints, but rather, seem to be connected either with the Roman fertility festival of the Lupercalia (Feb. 15) or with the mating season of birds." Encyclopedia Britannica

Some things are best left unexplored, and one is how the death of two men in the third century and the sex life of a tern or a sparrow have led us to send one dozen red roses, one lacy card, one heart-shaped box of chocolates or some other romantic trifle to the one we love each Feb. 14.

Let us concentrate, instead, on fertility and all the things people have tried through the centuries to produce -- if not love, at least compliance -- on the part of their mates.

A dinner composed of things historically considered aphrodisiacs would certainly begin with that favorite of Casanova, oysters, or perhaps truffles, though as long ago as 1874, a book called "Fungi" was reporting sadly that, "Truffles are no longer regarded as aphrodisiacs."

Next, bird's nest soup, which, New Biology reported in 1959, was alledged to have ashrodisiacal qualities.

For a salad, tomatoes, once called apples of love and thought to inspire that emotion in any who ate them. You might also serve the sweet potato, considered a producer of passion in the 1600s. Both of these homely vegetables achieve their reputations because they had just been introduced to Europe from faraway places.

As always, it is rarity and high cost that convince people a given item is an aphrodisiac. (In the days of showgirls and their like, one mink coat, taken externally, was discovered to be a potent love portion.)

There are only two things that today's encyclopedia lists as aphrodisiacs: Spanish fly (cantharides) and a substance derived from the bark of the Yohimbe, a tree found in Central Africa. Since both can give serious toxic, even fatal, effects, it is a case of see Rome and die.

We may as well do as people always have done: Choose a rare and costly food and imbue it with magical powers. With caviar out of favor, that leaves steak.

Turning from passion to romance, Valentine's Day would be well-celebrated with the heart-shaped dessert, coeur a la creme.

To make it, force one pound each of cottage cheese and cream cheese through a sieve, add a pinch of salt and stir in two cups heavy cream, blending well. Scoop into a heart-shaped mold or basket, lined with cheesecloth, and set it in the refrigerator overnight to drain. Put a fairly deep plate underneath to catch the drippings.

To serve, unmold, decorate with strawberries and serve with crackers. This, by the way, is not a particularly sweet dessert.

Little Caledonia, 1419 Wisconsin Ave. NW. has a limited supply of the individual white china coeur a la cream molds for $6 each. The larger molds can be ordered from Williams-Sonoma, Mail-order Department, P.O. Box 3792, San Franciso, Calif. 94119, or by calling toll-free, 800-358-9151. They are $17.50 plus $2.35 postage.