Mark as one of the signs of fashion progress in 1985 the increased respect (and attention) by designers and stores for the market potential of large-size women. In '84, design houses such as Anne Klein began to focus on petites. This year, added to Hubert de Givenchy and others who designed for larger women, were stores that expanded their departments for large sizes and a specialty store new to the area, the Forgotten Woman, focusing on highest quality designs for the not-so-slim.

There is also a good new book for larger women who need to break out of the "sausage" mold, encasing their figures in tight clothes that in fact make them look more zaftig and far less attractive. It's called "Breaking All the Rules: Feeling Good and Looking Great No Matter What Your Size" by Nancy Roberts (Viking, $17.95.) It is addressed to the one in three women, about 30 million in all, she says, who wear clothes Size 16 and larger.

"I'm not against losing weight," says Roberts. "I'm against dieting." Along with giving up diets, she abandoned guilt and self-loathing, she says. "But then I had to face up to the fact that I didn't just think I was fat . . . I was fat." She gave herself two alternatives: accepting the stereotype "or I could try to do something about it. I could try to alter the way our society views fat."

She pursues that goal in her book, showing the attractiveness of going against the old rules about large women not wearing bold colors, frilly dresses, double-breasted jackets, horizontal prints and more. She encourages shopping outside normal departments (including men's departments), wearing lots of accessories ("you have plenty of room for them"), experimenting with hair, makeup and color. "My pet hate is clothes designed to be slimming," she says.

There are plenty of women in this town, hardly model size, who don't need designers or a book to tell them how to dress freely and becomingly. Among them, Andy Smull, who wears simple easy-fit clothes in splendid fabrics and lots of imaginative and amusing jewelry from her own shop on Connecticut Avenue.