Red and yellow leaves are only part of the visual Octoberfest. It's time for the vegetable spelndors. These days, the most prosaic supermarket bin glows with the harvest moon orange of pumpkins, the purple of eggplants and the scarlet and green of late summer peppers. The red cabbage's red is as richly dark as flowing burgundy. And look at the way green, magenta and white shade into each other on those turnips!

Happily, the October vegetables can be as good to eat as their colors are to contemplate. Acorn squash baked with butter and brown sugar is consolation for the way the local corn is getting tough. A dish of brussels sprouts studded with leeks and chestnuts can make you forget spring's asparagus. Even the tomatoes that linger in the pale green stage on the end-of-summer vines have their uses. Sliced and fried with onions and a bit of bacon, they're by no means failed red tomatoes but rather a distinctive taste satisfaction.

It's time to rediscover rutabagas and the potentialities of cabbage. Time, even, to be converted to eggplant.

Here are a few ideas for making the most of the season's bounty.

CABBAGE PIE (6 servings) Pastry for 2-crust pie 3 cups shredded cabbage 1 medium onion, sliced 3 tablespoons butter 1/2 cup cottage cheese 3 or 4 scallions, minced 1 teaspoon chopped fresh tarragon or 1/2 teaspoon dried Salt and freshly ground pepper to taste 4 hard-cooked eggs, sliced

Roll out pastry and line a 9-inch pie plate. Refrigerate. Stir-fry cabbage and sliced onion in butter 4 or 5 minutes or until barely tender. Whiz cottage cheese and scallions in blender or food processor. Stir into cabbage mixture along with tarragon. Salt and pepper to taste. Distribute half of cabbage mixture in pie shell. Arrange sliced eggs on top. Cover with remaining cabbage mixture. Cover with remaining pastry. Press edges of crust together and crimp edges. Cut 2 or 3 slashes in top crust. Bake at 400 degrees 15 minutes, reduce temperature to 350 and bake another 20 to 25 minutes. Crust should be lightly browned.

CABBAGE CRUST SPINACH PIE (6 to 8 servings) 1 small cabbage Butter for pie dish 2 pounds fresh spinach or 2 10-ounce packages frozen 4 scallions, minced 2 cups ricotta cheese 6 tablespoons grated gruyere cheese 2 egg yolks, lightly beaten 2 tablespoons pine nuts 2 tablespoons raisins 1/2 teaspoon curry powder 4 tablespoons butter

Parboil cabbage 10 minutes, or until leaves are pliable. Drain. Discard core and separate leaves, cutting off any tough parts at the lower end. Drain thoroughly. Butter a 9-inch pie dish generously and arrange cooked cabbage leaves around bottom and sides, overlapping to form a crust. Leaves should extend an inch or so above the edge of the pie plate and the crust should be two leaves thick. Set aside.

Wash fresh spinach and cook with minced scallions a few minutes in only the water clinging to the leaves. If using frozen spinach (and for this purpose, it's very good) cook just enough to defrost in minimal water. Either way, drain very thoroughly. Chop spinach, press out remaining liquid and mix spinach with all remaining ingredients except butter. Arrange in pie pan and fold cabbage leaves over to form a border, leaving the center uncovered. Dot with remaining butter. Bake at 325 degrees 20 to 30 minutes, or until filling is set.

TWO TURNIP SALAD (4 servings) 1/4 cup bland salad oil 1 clove garlic, crushed 1/4 teaspoon mustard Juice and grated rind 1/2 lemon 1 cup grated raw white turnip, unpeeled 1 cup grated raw rutabaga 1 bunch scallions, minced Salt and pepper to taste 1 teaspoon minced parsley

Mix oil, garlic, mustard, lemon juice and lemon rind. Stir in turnip, rutabaga and scallion. Season to taste with salt and pepper. Garnish with parsley.

SESAME TURNIPS (3 to 4 servings) 3 to 4 tablespoons bland salad oil 2 tablespoons sesame seeds 2 cups grated raw white turnips, unpeeled 2 cloves garlic, crushed Salt and pepper to taste

In 1 tablespoon salad oil, saute' sesame seeds until golden brown. Set aside. In remaining oil, stir-fry turnips and garlic until tender. Season with salt and pepper and stir in sesame seeds.

RATATOUILLE STUFFED EGGPLANT (4 servings) 1 large or 2 medium eggplants 4 tablespoons olive oil 1 onion, sliced 2 cloves garlic, crushed 2 green peppers 3 zucchini, sliced 2 ripe tomatoes 1 teaspoon tomato paste 1/4 teaspoon dried thyme or 1/2 teaspoon fresh Salt and pepper to taste

Split eggplant or eggplants lengthwise and scoop out center, leaving 1/2-inch shell. Coat with olive oil, inside and out. In remaining olive oil, saute' the eggplant scooped out of these shells with the onion, garlic, green pepper, zucchini and tomatoes. When they are tender, stir in tomato paste and thyme, adding a little water or tomato juice if mixture seems dry. Salt and pepper to taste. Spoon into eggplant shells and place in a baking dish with 1/2 inch water. Bake at 350 degrees 30 minutes or more, until eggplant shell is tender enough to eat along with the ratatouille filling. Serve hot or cold.

MAPLE WALNUT RUTABAGAS (4 servings) 2 medium rutabagas 4 tablespoons butter Salt and pepper to taste 1/2 cup walnuts, ground 2 tablespoons maple syrup

Peel and slice rutabagas and cook until tender in boiling salted water. Drain and mash with half the butter. Salt and pepper to taste. Arrange in shallow baking dish. Saute' ground walnuts 2 minutes in remaining butter. Add maple syrup to the walnuts and distribute evenly over top of rutabagas. Bake 10 minutes at 400 degrees.

LEEK SALAD (4 servings) 1 pound leeks, washed and sliced 2 tablespoons salad oil 1 clove garlic, crushed Juice and grated rind 1/2 lemon Pinch thyme 1/4 teaspoon mustard Salt and pepper to taste 1/2 cup chopped mustard greens 1 small carrot, grated

Clean leeks well and boil in salted water until barely tender. Drain and cool. Combine salad oil, garlic, lemon juice and rind, thyme and mustard, adding a little salt and pepper. Combine leeks and mustard greens and mix with oil dressing. Garnish with grated carrot.