OH, YES, fried chicken. And hamburgers. The Fourth of July is as tradition-bound as Thanksgiving. You gotta have potato salad and watermelon and all the usual summer bounty we give sweltering thanks for in this first of our harvest festivals.

But in another month even the picnic fare we dream of all winter will begin to pall. What, hamburgers again? And another bowl of potato salad? So we begin to search our cookbooks for non-spill, non-spoil picnic food. There's no better source than the Wolf Trap Picnic Cookbook, for it has been inspired by one of the world's most sophisticated and imaginative picnic sites. Spectacular music in the glorious setting that is Washington's world-renowned Wolf Trap Park--what else would one expect to accompany it but marvelous picnic food.

Here is an example in which the new standby, tabbouleh, is adapted to picnic portability. It is also arranged attractively enough to serve as the party's centerpiece. All it takes is a dash through the express lane of your supermarket and perhaps a side trip to the garden for optional ingredients plus some salt, pepper and olive oil on your shelf. As for the preparation, it is nothing but a quick chopping and layering of vegetables, though it does require enough advance planning to let it sit overnight in your refrigerator,

EXPRESS LANE LIST: bulghur, lemon juice, scallions, celery, parsley, tomatoes, green peppers, cucumbers, mint (optional) and lettuce (optional). PORTABLE PICNIC TABBOULEH (8 servings) 1 cup uncooked bulghur 1/2 cup olive oil 1/3 to 1/2 cup fresh lemon juice (or to taste) 1 cup (about 1 bunch) scallions, finely chopped, including green tops 1 cup celery, chopped 1 cup parsley, chopped (or half parsley, half watercress) 1 cup fresh mint, chopped (or 2 tablespoons dried mint) (optional) 3 tomatoes, finely chopped 3 green peppers, seeded and finely chopped (optional) 2 large cucumbers, peeled and chopped 2 teaspoons salt Freshly ground black pepper, to taste Lettuce leaves (optional)

Use a large glass jar or canister (1 1/2 to 2 quarts), with a screw-on top, if possible; or a deep, large glass bowl that can be easily covered; or a stoneware crock.

Place the bulghur in the bottom of the container. In a small bowl, mix the oil and lemon juice, and pour over the bulghur. Add the vegetables in layers, in the order listed above. Sprinkle the last layer (cucumbers) with salt and pepper. Cover and refrigerate for at least 24 hours, or until the bulghur has expanded and is a light tan in color.

Just before serving, shake the jar well, or toss the salad to blend the ingredients completely. For easy picnic eating, spoon a serving of salad onto a large lettuce leaf, roll up, and eat with your fingers.