FOR the 30 million American women who wear size 16 and larger, Barbara Bush's arrival in the White House this month may be cause for celebration. Not since the era of Bess Truman, Mamie Eisenhower, and Eleanor Roosevelt has the nation had a First Lady who could be described as ``full-figured,'' even though one out of every three adult women in the country falls into this category. With her cloud of undyed, unlacquered hair, her trademark strands of large faux pearls (worn, she says, to hide a wrinkled neck), her minimal makeup, and her Rubensesque figure, Mrs. Bush stands in sharp contrast to Nancy Reagan's size-2, picture-perfect appearance. And unlike Mrs. Reagan, whose well-honed fashion sense led to a flap over borrowed designer clothes, Mrs. Bush has freely admitted through a spokeswoman that ``fashion is just not her thing.''
Speaking of Mrs. Bush's new role, Carole Shaw, founder and editor in chief of BBW - Big Beautiful Woman, a fashion magazine for large-size women - says, ``I think it's going to be a very nice breather for women of all sizes. Here's the No. 1 lady in the land.... She's a real person. I don't think she's going to set any great fashion trends, but that's OK. We've had so much emphasis on looks - so much emphasis on the package, and not what's inside.'' Mrs. Bush's reign as First Lady coincides neatly with what Ms. Shaw sees as a subtle change in women's fashion magazines. ``Curves are coming back,'' she explains. ``Now magazines are saying, `You're more than your body image.'''
That message has been gaining acceptance in other ways as well in recent years. Frustrated by the lack of stylish clothes in anything larger than size 14, a small band of not-so-skinny female entrepreneurs began to fight back. They opened stores bearing names such as The Forgotten Woman and 16-Plus. They started magazines and modeling agencies. They even created mail-order catalogs to market lingerie for large-size women.
As Shaw puts it, ``We don't believe fat is where it's at, or thin is where it's at. We believe alive and happy is where it's at, and beauty comes in all sizes.''
But on the scales that measure women's weight, there will always be a swing between the ideal of Twiggy and the reality of Jack Sprat's wife. So pervasive is the national obsession with thinness that teen-age girls still suffer from anorexia. Even healthy teens look at photos of Marilyn Monroe and say, ``She's fat.''
That is no longer a charge anyone can hurl at Oprah Winfrey, whose dramatic 67-pound weight loss sent a powerful thin-is-in message across the nation. In another high-visibility weight-loss plan, Deborah Coleman, the chief financial officer of Apple Computer Inc. in Cupertino, Calif., will soon begin a five-month leave of absence to shed at least 60 pounds.
Still, some sort of a modified rebellion is on, and time may be running out on both parts of the Reagan-years slogan, ``You can never be too rich or too thin.''
The new First Lady plans to support literacy drives and educational programs for poor children. Such an agenda promises that substance may count more than appearance in the Barbara Bush administration.
Let Raisa Gorbachev win the cool war of chic next time around. If trimming the budget comes before trimming the waistline, who will argue with the priority?