Gourmet supermarkets are springing up like chanterelle mushrooms after a rain. They amount to enormous food boutiques, pampering customers with Tiffany stained-glass windows over the checkout counters, salad bars, black-tie premieres, and skylights. They offer fresh New Zealand strawberries, French butter from Normandy, rattlesnake filets, Norwegian salmon, $15-a-pound cheeses, buffalo steaks, and French bread (baked on the premises). Camelburgers, anyone? That, too, at $11.99 a pound, frozen.
''I can't contain myself!'' says Louise Lonski of Adelphi Park, Md., as she paws happily through the fresh produce at the new Giant gourmet supermarket in Rockville. Mrs. Lonski decides to go for the chanterelles, golden mushrooms that look appropriately gilded, at $14.99 a pound.
She was searching for celery root for one of the French, German, or Indonesian dishes she loves to prepare, but they were temporarily out of it. On the other hand, she could browse through a garden of gourmet delights: white radishes looking like long, ivory mouse tails; haricots verts or French green beans; lily root gooseberries; fresh herbs; and those ruby New Zealand strawberries, $4.99 a pint.
''Cooking is a hobby of mine. . . . I'm going over there to the meat section to get some buffalo meat for next week,'' says Martha Bennett of Clarksville, Md. She's just stopped off at the supermarket's salad bar on her way back to work.
''They have fresh game, fresh baked goods made right here, a fresh pasta section, fresh seafood. We've already tried the squid, and we're going to try the rattlesnake,'' Mrs. Bennett says. The store also offers standard supermarket items, plus a flower shop, pharmacy, pasta shop, savings and loan branch, and reading center.
Everyone may not be as adventurous as Mrs. -Bennett, but there are enough shoppers out there interested in experimenting with gourmet food to generate sweet profits.
''It's taking off around the country in the number of products offered and the number of people buying,'' says Timothy Hammonds, a senior vice-president at the Food Marketing Institute, whose members represent half the grocery businesses in the United States.
The phenomenon is so new that specific industry studies are nonexistent. Chicago economics consultant Bill Bishop, an expert in tracking retail food profits, says, ''It's a trend that's excited buyers, although there are only a handful of the stores now, maybe 250 stores that fit into the gourmet supermarket category out of 29,000 supermarkets in the US.''
Mr. Bishop, head of the Chicago economics consulting firm Willard Bishop Company, estimates those supermarkets generate sales of between $250 billion and the stores, are already generating $2 billion to $3 billion a year in sales themselves. And a higher percentage of their sales is profit.
If the experience of Grand Union is any indication, ''trading up,'' as the idea is known in food circles, may be the wave of the future. Gary Perino, public-relations manager of the Grand Union chain, says GU opened an experimental gourmet supermarket called Food Market in 1979 and found it so profitable that it has converted 100 of its 600 stores to the new prototype.
''It's not unusual for sales to double when we've installed this concept,'' he says, adding that under a current five-year development plan, Grand Union will be converting the bulk of its stores to this format. (The Eastern chain, which operates as Grand Union in 15 states, also goes by the names Big Star in the South and Weingarten's in Texas and Louisiana.)
Grand Union's Food Market in Rockville is the one with the Tiffany-style stained-glass windows casting a reverential glow on the checkout counter. GU has hired the celebrated designer and illustrator Milton Glazer to advise on touches like that, as well as the colorful graphics that liven up the maple-paneled store, one of the upscale series Mr. Perino describes as ''a theater for food.''
Its new concept, called Food Centers, includes a large piazza in the center of the store for a 200-seat restaurant.
In contrast to this affluent approach, Grand Union, like some other supermarket chains, is also running a polarized operation on the other end, with 20 ''Basics Stores,'' no-frills warehouse shopping centers with generic foods at bargain-basement prices.
If that thundering economist Thorsten Veblen were still around denouncing ''conspicuous consumption,'' he'd blanch at all those supermarket carts piled high with 50 different kinds of pate (of which Safeway boasts). The California-based supermarket chain has been experimenting with trading up via its new Bon Appetit stores, bearing the magazine's logo on its shops and offering customers recipes for that month's gourmet dishes.
Some of its stores, still a small sprinkling in Safeway's nearly 2,000 supermarkets, have skylights and California decor (natural wood, plants, and country-kitchen touches) says Louis Gonzalez, public affairs manager for the San Francisco division.
For customers used to the standard meat, potatoes, and iceberg lettuce supermarket, gourmet supers are dazzling. Giant's year-old experiment called ''Something Special,'' in McLean, Va., is to grocery shopping what the Paris collections are to couture: a heady ambience in which to drop a lot of money.
Flawless, fresh fruits (five varieties of pears) and vegetables nestle in their own wicker baskets or white serving dishes, or rest upon a throne of shaved ice. Fresh octopus, gleaming pale gray and tentacled, rises from more ice (decked with orange slices) in the seafood department, along with Spanish red shrimp ($14.99 per pound), and whole Norwegian salmon.
The meat department includes exotic cuts that may offend preservationists: llama round steak, camel steak, bear round steak, a whole suckling pig at $65. A deli counter offers bluefish pate, fig and almond torta cheese at $15 a pound, fresh black truffles at $250 a pound. A bakery displays fragrant bread and rolls , and $20 fruit flans and other pastries.
There are aisles full of exotica such as walnut oil, rose water, Szechuan peppercorns, fresh flowers from mimosa to orchids, gleaming copper cookware and utensils for sale in a building that looks like a department store for food. It is an almost stately looking store, like a series of food boutiques grouped together in one vast area with a tasteful cedar exterior, an interior with harlequin-patterned brown and white floor, natural pine walls, fruit-and-flower decor, and bright graphics.
The McLean ''Something Special'' store opened in suburban Virginia with a black-tie premiere for 900 people, a hint (if you didn't know it before) that McClean has one of the highest income levels in the country.
The city was ideal as a test market, says Giant's -director of public affairs Barry Scher, ''because it's a more affluent population, with lots of embassies and VIPs within a few miles of the shop.'' The Washington-based food chain, with its 155 stores, has had a steady parade of rival supermarket executives visiting both the McLean and Rockville stores to dish up new ideas, Mr. Scher says.