SURE, Thanksgiving is turkey and stuffing and pumkin pie. But it's a lot of other delectations as well.

For some, the Thanksgiving sweet potato is equally important. Not to mention the Sweet Thursday cranberry, appearing in conserve, relish or sorbet. There are people who pay little attention to turkey but look forward all year to a late November rendezvous with walnut-garnished creamed onions.

Even those who grant the big bird its star spot admit that the supporting cast makes a difference. This, after all, is where Thanksgiving offers choices. Tradition mandates no single soup or salad or vegetable. It's possible to skip potatoes altogether in favor of an early American spoon bread. There's more than one way to deal with the cranberry.

So, instead of settling for frozen peas, why not accompany the holiday fowl with a vegetable medley, combining leeks, carrots and zucchini? Or a melange of Brussels sprouts, minced green onions and cubed rutabaga?

The secret of a good vegetable bouquet is to stagger the cooking time to meet the tenderizing requirements of different vegetables. Carrots, Brussels sprouts and rutabagas take longer to cook than celery, leeks, summer squashes or broccoli.

For a carrot, leek, cabbage and mustard green combo, for example, start the carrots in boiling salted water first, add the leeks after five minutes and bring on finely shredded cabbage and mustard greens for a final two or three minutes. Colors and textures as well as flavors remain well differentiated that way.

When it's salad time, make sure there's a real palate refresher to interrupt the succession of rich festival foods. Much-maligned iceberg lettuce can't be faulted for lightness and crunch. Teamed with a bit of watercress or chopped mustard green for tang, it can make an ideal Thanksgiving salad.

Thanksgiving is also an occasion for reverting to the Victorian ice as a palate cleanser. Commercial lemon sherbet takes on the necessary tartness with the help of extra lemon juice, shredded lemon peel and a touch of dry white wine. Homemade cranberry ice has everything the situation requires.

Here are a few of the options.

POTATO-ONION CASSEROLE (6 servings) 1 pound onions, peeled and sliced 1 1/2 cups peeled and sliced potatoes 1 clove garlic, sliced 1/2 cup chopped celery stalks and leaves Salted water to cover 2 eggs, beaten 1 cup milk 1 bunch green onions, chopped 2 tablespoons butter 1 tablespoon toasted bread crumbs 1 tablespoon grated parmesan-style cheese

Simmer onions, potatoes, garlic and celery in salted water until vegetables are tender and cooking liquid is almost gone. Place vegetables and remaining liquid in a 2-quart baking dish. Combine eggs and milk and pour over vegetables. Saute' chopped green onions in butter until tender. Sprinkle on top of vegetables in baking dish. Add cheese and bread crumbs and bake at 350 degrees 25 minutes or until liquid has set.

SWEET POTATOES WITH PECANS (6 servings) 6 medium-sized sweet potatoes 3 tablespoons butter 3/4 cup chopped pecans 2 teaspoons Worcestershire sauce

Bake sweet potatoes in a 350-degree oven 20 minutes or until tender. Discard skins and mash potatoes with 2 tablespoons butter. Saute' pecans in remaining tablespoon of butter and when they begin to brown, add Worcestershire sauce. Place sweet potatoes in serving dish and mix in half of pecans. Top with remaining half.

OLD-FASHIONED CREAMED ONIONS (4 servings) 1 pound small white onions Salted water to cover 1 teaspoon flour 1 teaspoon sherry or Madeira 1/4 cup light cream

Peel onions and simmer until tender in salted water to cover. Drain, reserving cooking liquid. Stir flour into liquid gradually and mix well. Add sherry and cream, return to onions and reheat.

CRANBERRY ICE (6 servings) 2 cups or 1/2 pound fresh cranberries 4 cups cranberry or cranapple juice Juice of 1/2 lemon 3/4 cup sugar

Simmer cranberries and juice in a 2- to 3-quart saucepan until berries begin to burst, approximately 10 to 12 minutes. Add lemon juice and sugar and stir until sugar is melted. When cool, pure'e berries in blender or food processor. Freeze in ice trays or glass bowl, stirring and mashing every half hour for 2 hours. Just before serving, pure'e again in food processor or blender.