More and more Americans are eavesdropping on the world with shortwave radios, tuning in stations from Tahiti to Venezuela and boosting sales in an elite niche of the consumer electronics market.

The radios, some as small as a paperback book and costing less than $100, allow armchair adventurers to pick out broadcasts from some of the nearly 160 countries on the air.Tad Oki, Sony Corp. of America's product manager for shortwave radios, estimates that the company's U.S. sales have risen by 15 to 20 percent since the start of the decade.

Sony, the U.S. market leader, projects its U.S. unit sales will show a rise of 27.7 percent in 1988. But Oki calls the shortwave radio a mature product with a growing audience and only a fraction of the sales potential of hits like the Walkman miniature tape player.

Buyers of the radios include hobbyists, whose passion is identifying obscure stations around the globe, as well as an educated segment of the broader public seeking a fresh perspective on world events from foreign broadcasts.

Bob Hill, who works for a Massachusetts high-technology company and "eats shortwave radio for breakfast" according to his acquaintances, tries to ferret out the most elusive signals in the sky. His prize finds include stations in Nepal and Sri Lanka.

"Shortwave radio listeners are divided into two camps: those who enjoy the programs and those who love the thrill of the chase," says Hill. "I love the chase."

Fellow radio enthusiast Jerry Berg, a lawyer with the Massachusetts District Court System, boasts even more exotic discoveries -- in 1961 he heard Radio Katanga broadcasting from a breakaway province of the former Belgian Congo, now Zaire.

The growing appeal of shortwave radios to mainstream consumers is attested by their appearance last year in L.L. Bean Inc.'s mail order catalogs. L.L. Bean, whose quality products cater to unimpeachably conventional tastes, now offers three Sony shortwave radio models.

"We find that they sell very well," says Catharine Hartnett, a spokeswoman for L.L. Bean. "Otherwise we wouldn't be carrying them a second time around."

Although low prices entice some people -- portable models begin around $100 while the top of the line is pricey at more than $1,000 -- cost does not seem a major obstacle. Hartnett says L.L. Bean's most popular model, the Sony World Band Radio System, retails at $345.

"Once people get bit by the bug, $350 is nothing," says Dick Robinson, manager of Electronic Equipment Bank, a Vienna, Va.-based retailer that also sells shortwave radios by mail order.

Joshua Landis, a doctoral candidate in the Near Eastern Studies Department of Princeton University, says he listens to the British Broadcasting Corporation's World Service on his $160 shortwave radio because he finds its coverage of foreign events far superior to that of U.S. news organizations.

"It was crucial for the Libyan bombing," said Landis, referring to the United States air strike against Tripoli in the spring of 1986. "For five days there was not one dissenting voice in the U.S. media. They were only interviewing chest-thumpers like (Defense Secretary) Caspar Weinberger who were saying what a wonderful thing this was.

"The BBC had people in the field asking about (the implications of the bombing on) international law, would it (the air strike) really solve the problem?"

The rising sales of shortwave radios partly reflect technological improvements over the past decade, according to radio experts.

It no longer requires a safe-cracker's touch to tune the radios because many now have digital readouts, allowing listeners to key in the exact frequency they want to hear, says Larry Magne, editor of a guide to shortwave stations.

The guide, "Passport to World Band Radio," gives schedules and frequencies for radio stations in almost 160 countries, ranging from Albania to Zaire.