It's 11:30 p.m. Sunday and I'm still wrestling with the age-old problem facing us superior mothers and gourmet cooks: what to pack for school lunch tomorrow.

David, my eldest, is, at 14, a devoted son, a serious student and more handsome than Paul Newman. He also has an exquisitely honed culinary sensibility. With one sniff he can put down a low-grade caviar, [WORD ILLEGIBLE] point the very minute a Dover sole lost its life. With a flick of his fingernail he determines the original of an artichoke or the readiness of a quiche.Or, by only casting a side-long glance, he can unravel the secret of an esoteric mushroom. And if, Heaven forbid, the eggplant under the parmegian didn't sweat it out first, he's the first to notice.

Needless to say, preparing lunch for my juvenile gourmet is a tremendous challenge. First, there is the problem of planning. Sitting on my desk right now, fo example, are some resarch tools: "Mastering the Art of French Cooking," three more books on gourmet French, cooking, four cookbooks dealing with ethnic food, one which explores the use of wine in cooking, and two specialty books - one on hamburgers and one put out by the Women's Strike for Peace (called Peace de Resistance).

David knows I regularly consult these books in preparing his luncheon menus. I also keep a thick file folder on the desk wherein I file, by date, the lunch menus for the preceding six months. This guarantees I will not err on the side of monotony.

Now I seize my legal-sized lined yellow pad of paper, together with the carbon, on which I work it all out in writing. All of this, of course, is done with the utmost secrecy. I am a firm believer in the psychological benefits of a surprise at lunch time.

At the crack of dawn, I greet David with a cheery "hello" when he enters the kitchen, where I'm preparing a hearty meal to start his day off right. As the time draws near for his departure, I go to the refrigerator for his lunch and gingerly place it on top of the school materials in his book bag.

As he kisses me goodbye at the front door, he slings the faded green canvas book bag through one arm, then the other, until it clunks - all 14 pounds of it - on his back. "Have a good day," I call after him as he races down the block to catch the 7:20 bus.

With some luck, he tells me, he locates a vacant seat on the bus and plunks down on it, book bag squeezed in behind him, for a 25-minute ride. Once downtown, he transfers to the crosstown bus, racing across the street to make the connection his book bag bouncing all the way like a rowboat in a tidal wave. Being an extremely polite young man, whenever possible David makes way for adults to board the bus first, so that he often is the last one in before the door is forced shut. He says he cringes each time the door slams and pinches his book bag behind him.

When he finally reaches school around 8:45, he promptly forgets all about his gourmet lunch.

All his faculties are directed toward such things as English I, integrated math and Spanish II, not to mention tennis and girls.

The book bag cum lunch accompanies him from class to class. As he takes books in and out the lunch often ends up crushed, between "A History of Rome to A.D. 565" and "Physical Science for Progress."

Fifth period comes at last. Lunch time: For the 74th time David thumps the book bag down beside him. He reverently reaches inside and pulls out a small, tired-looking brown paper bag containing, he discovers, one blemished apple, three carrot sticks, and a squooshed peanut butter and jelly sandwich. So traumatizing were all the shocks sustained by my tenderly prepared epicurean delight snce it left my kitchen, that it suffered a metamorphosis.

That's my story and I'm sticking to it.