Hans Stern has been making South America a more expensive place to visit for a long time. Now he's doing the same for much of the rest of the world.

Stern, Brazil's jewelry king. opened his 180th store here last fall and plans to add 20 more to his empire before 1980.

Almost alone, Stern has taken Brazil's colored gems such as aquamarine, tourmaline and imperial topaz from obscurity and made them respectable citizens of the jewelry world.

He is the world's largest dealer in what used to be called semiprecious stones -- gems that are not diamonds, rubies, emeralds or sapphires.

"That's an artificial distinction," Stern said when "semiprecious" was mentioned. In the last 10 years, good quality Brazilian stones have increased in value 20 percent or more per year, Stern said, and they are becoming rarer. The last strike of imperial topaz, for example, was 17 years ago.

Brazil provides about 90 percent of the world's supply of coloted gems and most of it passes through Stern's empire, which is unique in the jewelry business in encompassing every procedure from mining to jewelry design and retailing.

Stern, 56, was a 23-year old refugee from Nazi Germany when he set up his business in Rio and from the beginning he relied on a lot of promotion to sell his wares.

He noticed that tourists from the United States and Europe rarely visited a single South American nation, but usually made a tour.

Agents were posted in airports and hotels throughout the continent to make sure the tourists learned of H. Stern. Tourists were given free charms and told they could ick up another charm in each country on their itinerary. Upon reaching Brazil, they could get a bracelet to hang the charms on by visiting a Stern store.

If the charms didn't get them, maybe the free limousine service from their hotel to H. Stern and back would. And, if the tourists worried about being cheated, they could rest easy with Stern goods. Any Stern bauble can be exchanged or returned for cash for any reason within a year of its purchase.

If Stern agents are attentive before a customer gets to the store, the company is almost solicitous afterward. Customers get cards on their birthdays and at Christmas and many get letters asking how they like their Stern gems.

The only people who are nore closely watched then customers are employes. "Honesty" is a word that comes up often in conversation with the genteel and gentle Stern. It is obviously troubling to have so many small items of large value lying around unless the people handling the gems can be trusted.

The company administers a complex series of aptitude and psychological tests to prospective employes in an attempt to evaluate their characters. If they make the grade, they join a company that (in Brazil) provides full medical and dental care and subsidizes their lunches.

About 80 percent of Stern's 2000 employes are women because, Stern says, "they are more honest, steady and loyal." One of four top managers and about half of the second-level managers are women, Stern said.

In one area of his operations, Stern said, he has failed to find honest men or women -- mining.

"You're bound to lose money if you don't live at your mine," Stern said. "The right of first refusal on stones belongs to the miner," he joked. "In my 30 years in gems, I've never made a nickel mining."

But he keeps on trying. "Every gem dealer dreams of finding something really big," he explained. "Someone always comes up with a story of a fabulous area, honest people, etc."

Stern started inbusiness with $200 capital. Now he has an inventory of 250,000 pieces of jewelry, not counting unset stones which make up 20 percent of Stern's sales. His workshop turns out 10,000 new pieces each month.

Asked what his annual sales total, Stern turns the question aside. "I'd be happy ot answer other questions," he said.

The aquamarines, tourmalines and imperial topazes that are the principal Brazilian gems are very similar to the precious stones. In fact, the only difference between emeralds and aquamarines is color. They have the same hardness and chemical composition, but the aquamarine is a light blue.

Stern's personal favorites are tournalines, which come in a spectrum of colors from green to red.

As more and more manganese is added, the green tourmaline turns to red -- and also picks up imperfections. A piece of tourmaline half red half green is called watermelon.

Stern has a private collection of tourmalines in which he includes fine examples of every hue. He has a second private collection which will have about 250 stones -- one excellent example of each kind of gem.

And while other leading jewelers maintain a facade of quiet reserve, Stern keeps thinking of new ways to lure customers into his stores and keeps opening new stores to make it easier for people to run across his jewels.

"Promotion" is his one-word answer to how he has built H. Stern into one of the four largest jewelry businesses in the world (along with Harry Winston and Tiffany & Co. of New York and Bucherer of Switzerland).

In his elegant Fifth Avenue store last fall, Stern handled his stack of multilanguage brochures, Christms cards, offers of free charms and other promotional material with almost the same enthusiasm he showed for a large piece of watermelon tourmaline, a couple of giant pieces of imperial topaz and a $40,000 emerald necklace.