SURE, WE PUT them raw in salads. Sure, we make sauce of them with onions and green peppers. Sure, we slice them, salt them and eat them with cottage cheese or hamburgers. All signs suggest that tomatoes are vegetables. But the truth of the matter is, tomatoes are fruits.

Or at least that's how botanists classify them. They are grouped along with apples, peaches, pomegranates and pears, in that they are comprised of fleshy pulp whose purpose is to protect mature seeds within. Technically speaking, spinach, cabbage, broccoli and cauliflower are vegetables: we eat their greenery before they fruit. But tomatoes, along with green peppers, eggplants and summer squashes, actually are fruits in a botanist's eyes.

All these hair-splitting technicalities do not really change the way tomatoes taste, nor need they change the ways we like to use them. But reconsidering tomatoes as fruits might open up a whole new world for tomato-lovers. Get to know them as sweets, and tomatoes take on an altogether new flavor.

Tradition provides us with a few examples of this use of tomatoes already. Occasionally an old-time cookbook offers a recipe for tomato preserves. Those who have tried such recipes recently, with the full variety of tomato hybrids available today, suggest that the small yellow pear tomatoes, bred for their low acidity, taste better sweetened in the jar. And southern cooks, with their penchant for sweetening everything, make a tomato pudding that tastes more like dessert than a vegetable side dish, even though they often serve it with country ham and grits.

But start to think about tomatoes as fruits, and your imagination carries you away on flights of bright-red fantasy. Tomato upside-down cake, tomato brown betty, tomato muffins, tomatoes over ice cream. Take some time to reflect upon the differences between tomatoes and the other fruits you use, and you'll be ready to transform your favorite dessert recipes into concoctions ripe with that favorite red summertime fruit.

Two significant differences emerge if you compare tomatoes with, say, peaches. First, there's the acidity. How acid a tomato tastes will depend not only upon the variety, but also on how it grew. A big, juicy tomato grown in optimum conditions will tend to have a less acid flavor than a small, tight, early tomato. But this distinction brings up the other characteristic that those who cook with tomatoes must remember. Tomatoes have much more liquid than other fruits we're used to using, liquid that won't always add flavor or character to your dish. If you're working with juicy tomatoes, squeeze the pulp and strain off the excess juice.

Tomato peel tends to add a bitter taste to anything with tomatoes in it, sweet or savory. And so the careful cook who wants to experiment with tomatoes as fruits will want to peel them as well as drain off the excess juice. Blanching tomatoes--perhaps the easiest way to separate skin from fruit--does tend to start the juices flowing, but it also softens the pulp, a process often desired if you wish to use tomato pure'e rather than chunks of tomato. Blanch as swiftly as possible, and quickly remove skins while keeping tomatoes whole until ready to use in recipes, to avoid losing flesh and flavor.

One way to convince friends and family that tomatoes really deserve to be considered fruit is to include them in dishes that combine them with other, more familiar fruits. You probably won't want to rush right out and cut up chunks of tomato to toss in with your favorite ambrosia fruit salad, but subtly blend a few tomatoes in with the peaches or apricots--especially with fruits that tend to taste too sweet for your liking--and you'll begin to discover the possibilities inherent in this fruit so long misunderstood and misrepresented as a vegetable. RED TOMATO BROWN BETTY (6 servings) 8 to 10 firm ripe tomatoes 1/2 cup butter 1 cup graham cracker crumbs 1 1/4 cups brown sugar 1/2 teaspoon vanilla 1/2 teaspoon allspice 1/4 teaspoon salt 1 cup quick-cooking oatmeal 1/2 pint heavy cream (optional)

Blanch each tomato 20 seconds, then dip in ice water 20 seconds to remove skins easily.

Melt 1/4 cup butter and mix with graham cracker crumbs. Press into lightly greased 8- or 9-inch casserole. Cut tomatoes into wedges, discarding stem end. Gently press excess liquid from tomatoes and drain off. In a large bowl combine tomatoes with 1 cup brown sugar, vanilla, allspice, salt and 1/2 cup oatmeal. Pour mixture into graham cracker crust. Mix together remaining oats, butter, brown sugar and salt and crumble mixture on top. Bake uncovered at 375 degrees for 30 minutes. Serve topped with optional heavy cream. SMITHFIELD TOMATO PUDDING (2 to 4 servings) 3 to 4 ripe tomatoes 1 tablespoon butter 2 day-old biscuits 1 tablespoon sugar 1/2 teaspoon vanilla Juice of 1/2 lemon 1 teaspoon flour

Blanch, peel, trim and chop tomatoes. Cut butter into small chunks; crumble biscuits. Combine all ingredients and place in 6-inch greased casserole. Bake at 350 degrees 30 to 40 minutes. TOMATO UPSIDE DOWN CAKE (Makes 1 1-layer cake) 3 to 4 firm, ripe tomatoes 1/2 cup, plus 1 tablespoon butter 3/4 cup brown sugar 2 tablespoons maple syrup Dash salt 3 eggs 1 teaspoon vanilla 1 cup flour 1 teaspoon baking powder 3/4 cup granulated sugar Whipped cream for topping

Blanch each tomato 20 seconds, then dip in ice water 20 seconds. Peel and slice into 1/4- to 1/2-inch slices, discarding stem end. Mash gently and strain off all excess liquid.

In 8- to 9-inch cast iron skillet or cake pan over low heat on stove melt 1/2 cup butter. Stir in brown sugar, maple syrup and salt. Let mixture sizzle about 3 minutes, then stir in tomatoes thoroughly. Turn off heat.

Melt 1 tablespoon butter. Separate eggs. Beat yolks until frothy. Beat in butter and vanilla and set aside. Sift flour and baking powder together and set aside.

Place egg whites in large mixing bowl and beat until soft peaks. Gently fold in sugar, then egg yolk mixture, then flour. Spread batter over tomato mixture. Place in 325-degree oven and bake 30 to 40 minutes until cake tests done. Turn upside down to serve and top with whipped cream.