ON AUG. 6, 1980, in Atlanta, Ga., a "new breed woman" stormed the last stereotypical bastion of "the old woman." You know, average age 48 with one husband and 1.8 children living in the suburbs and driving a station wagon albeit an import.

Sheila Hoban, aged 30, single, with a boyfriend, an illustration researcher at the Smithsonian, park naturalist for Fairfax County and a resident of the Dupont Circle area, didn't do it on purpose. Actually, she did it as a lark . . . entered the National Chicken Cooking Contest . . . and won the Grand Prize of $10,000.

"I'm embarrassed," Hoban admitted the next day on the phone from Atlanta where the 32nd annual contest had just concluded. "I just won $10,000 for four hours' work. That's not American. You're supposed to work for your money," she giggled, sounding rather blase for someone in that position. "No, I'm just hung over.

"I thought all contest winners had to be people who could do things with those little marshmallows, chunky hot dogs and macaroni. Apparently not. I don't know why I entered. I was standing in the checkout line and you know you have a choice of People, the National Inquirer or Family Circle. I'd already read People so I picked up Family Circle and there was a notice of the contest so I said: 'Well this is really American,' so I entered. It's the first time I ever entered any contest at all.

"Listen, there are people down here who enter every contest. They're like golf professionals. All they did here was sit around and talk about them: the Pineapple Classic which is held in Hawaii, the Pillsbury Bake-Off and all the ones they've entered."

Hoban won the local cook-off at Kitchen Bazaar three months ago with a chicken, an 11-ounce can of cream of chicken soup, a 15-ounce can of artichoke hearts, wine, mushrooms, cream and tarragon, a recipe she says she made up "based on what I like to eat and how my Great Aunt May likes to make chicken plus things Aunt May would never eat."

Like what? "Artichoke hearts."

And why did she think whe won over all those older, more experienced, professional contest enterers?

"Probably because I have more debts than any of the other contestants."

So now you don't have to ask the question: "What are you going to do with your winnings?"

At least Hoban likes chicken, although why is not completely clear. For one thing her kindly feelings about the birds have a lot to do with its price. "It's cheap." For another she has no intention of cooking it for some time to come. "Not after the last three days," she said as she was ready to leave Atlanta. "They fed us chicken for three days. They even made my recipe for the food editors [covering the contest] at 8 o'clock this morning. Yuck."

Besides, Hoban is tired of the chicken jokes her friends have been telling her for three months.

But it was all worth it, not just because of the $10,000 but because it was a perfect way to one-up her brother. At the end of the interview Hoban decided the real reason she entered the contest was the "unwritten competition" she has with her brother. "We each try to do something more unusual than the other one.You know, something your mother can tell at the hairdresser's so she can brag about her children, and your aunt can talk about at her over-50 club.

Hoban was hard-pressed to top her brother's discovery of a "diatom bloom that was 100 miles long." How can anyone top that, especially if they don't know what it is . . . or even if they do. A diatom bloom is what whales eat. Hoban's brother is a marine biologist and he discovered this wonder of nature, the length of it being the wonder, apparently, on a trip to Antarctica. Whales eat diatoms and no one, Hoban explained, knows wheher they are plants or animals.

"I don't know what he can do next," Hoban crowed. On the other hand Hoban doesn't think she's likely to win any more cooking contests. Betty Crocker she isn't.

Hoban may have set cooking contests back 50 years.

And the winner -- CAPITAL CHICKEN CASSEROLE (4 servings) 1 (3-3-1/4 pound) broiler-fryer, cut in parts 4 tablespoons butter 1 tablespoon oil 1/2 pound fresh mushrooms, sliced 1 tablespoon flour 1 (11-ounce) can cream of chicken soup 1 cup dry white wine 1 cup water 1/2 cup cream 1 teaspoon salt 1/4 teaspoon tarragon leaves 1/4 teaspoon pepper 1 (15-ounce) can artichoke hearts, drained 6 green onions, chopped 2 tablespoons chopped fresh parsley

In a large frying pan, place butter and oil and heat to medium temperature until butter melts. Add chicken and cook, turning, about 10 minutes, or until brown on all sides. Remove chicken and place in baking pan or casserole. In same frying pan, saute mushrooms about 5 minutes or until softened. Stir in flour. Add soup, wine and water; simmer, stirring, about 10 minutes, or until sauce thickens. Stir in cream, salt, tarragon and pepper; pour over chicken. Bake, uncovered, at 350 degrees for 45 to 60 minutes. Mix in artichoke hearts, green onions and parsley. Bake about 5 minutes more or until fork can be inserted in chicken with ease.