London — Any way you look at it, Stephanie Hoppen, a dealer in paper antiques, is involved in a business favored by timing. The best interior designers in many countries are seeking out antique prints, maps, and sketches to use in their top decorating jobs - and Mrs. Hoppen's particular stock in trade happens to be 17th-century prints of flowers and fruits, maps, vintage fashion sketches, and whimsical caricatures drawn between 1790 and 1850.
Just as what she terms ''weird and wonderful'' maps are attracting a growing circle of collectors, Mrs. Hoppen assembles her catalog called ''Cartographica Curios.'' The charm of these maps, she explains, lies in their very faults and fantasies as they beguilingly depict invented countries, myths, and misconceptions.
During a period when gourmet cooking has become an everyday event and haute cuisine is a topic of conversation in chic social circles everywhere, one more Hoppen specialty happens to be illustrated antique cookbooks published between 1600 and 1900. Present-day chefs now vie for her rare volumes, which contain the culinary secrets of the great chefs of the 19th century. Escoffier is in demand, of course, and ''Le Libre de Cuisine,'' by Gouffe, sells for (STR)250 (about $ 375).
Stephanie Hoppen is a rather vivid English entrepreneur who reigns over a quaint little shop at 17 Walton Street. It is in one of those enclaves of small specialty shops and restaurants that provide pleasant interludes during a London visit. One summer day recently, she even served a few guests a ''proper English tea'' in the tiny garden behind the shop and regaled them with stories about her growing transatlantic enterprise.
''I got into business backwards,'' Mrs. Hoppen explained. ''I was trained to be a barrister, a trial lawyer, in fact. But I had grown up in Capetown, South Africa, in an environment of collectors and collecting. Like my parents and my grandparents before me, I simply loved old things, especially books. When I came to London as a young wife and mother, I decided to leave law. A friend who knew my interests suggested, 'Why don't you go into books?' ''
Immediately she knew she would rather be a bookseller than a barrister. So, with $50 in capital, she ventured into the antique book business, going to auctions and sales, and learning as she went.
Soon her search for stock, which later expanded to prints and maps, was taking her to the Netherlands, France, Germany, Italy, and the Scandinavian countries. It was then she discovered that ''the whole world seemed to be looking for the same things I was. Sometimes I would come home empty-handed. Often I spent too much money. But I had to go and actually look at things.''
In those years she dealt from a closed office with museums, libraries, universities, and private collectors.
''It was moving to this funny little shop two years ago that changed the whole thing,'' she recalls. ''Suddenly the world was at our door. Visitors combed our shelves, and interior designers discovered our portfolios of antique prints. They were particularly drawn to the large botanical prints by Basil Bessler, who worked in London before 1713. The monumental task of making the plates for the series took Mr. Bessler 16 years to complete, and his prints now sell for $600 to $1,200 each.''
New York interior designer Mario Buatta, who has purchased prints from Mrs. Hoppen, has commented about them: ''Prints have become very popular because they are part of the whole return to traditional romantic decorating. I frame them with hand-tinted French mats in painted or gilt frames, and they make very effective wall decoration. I use the work of several printmakers, including Basil Bessler and Pierre Joseph Redoute. They used to be very inexpensive. Now they are very expensive, but very effective.''
This year, Mrs. Hoppen was invited to show at the elegant Winter Antiques Show in New York, at the New York Book Fair, and at the Californian International Antiquarian Bookfair. She will exhibit at the San Francisco Fall Antiques Show Nov. 3-6.
Russell Carrell, manager of the Winter Antiques Show, where Mrs. Hoppen will be the sole London exhibitor again next January, claims she brings something different to the show and that her antique volumes on food and beverage are especially pleasing to the growing number of cookbook collectors. Not for a century, he estimates, has there been such an avid interest in reading about fine food.
Now, the dealer says, Americans are by far her best customers. She finds them to be both discriminating and knowledgeable. If they don't know, she says, they ask. These days, the dealer says, some of her best leads for material come from such casual sources as dinner companions, or acquaintances who call and say, ''My aunt wants to sell her collection of . . . ,'' or a new friend who questions, ''Would you by any chance be interested in . . . ?'' Yes, she would be interested. That's what keeps new catalogs coming along.