A crime wave coinciding with the largest campaign ever to lure Americans to Brazil has forced tourism planners here to come up with a unique solution: holdup insurance.

Available by May, "tourism insurance" will reimburse future visitors for stolen cash, cameras, clothing, jewels and watches.The service comes on the heels of an airport poll that found that 15.5 percent of tourists leaving Rio -- Brazil's major destination -- had been robbed.

During the current South American summer, Rio's beachfront hotels are packed, but three incidents last month show that tourists are also victims of what has become a citywide crime wave.

Three armed men hijacked a Rio-bound tourist bus and robbed 39 Argentinian tourists of $30,000.

Six men armed with revolvers invaded a Rio hotel at midday and looted 140 safe deposit boxes of $85,000.

Two pickpockets -- known here as "beach rats" -- tried to steal a watch from a tourist on a popular Rio beach. In the ensuing scuffle the visitor was shot in the back and killed.

According to a survey released last month, one third of Rio residents polled had been held up, 92 percent considered crime in the city "very high," and in zona sul -- the fashionable area frequented by tourists -- 86 percent said they were apprehensive about walking on the streets. The poll also detected a hardening of attitudes towards criminals -- 44 percent supported lynchings and 20 percent backed the notorious "death squads" -- gangs of off-duty police who kill criminals.

Rio's newspapers have responded to the upsurge in lawlessness with full-page articles devoted to guard dogs and New York-style door locks. On Jan. 28, Rio's police chief resigned under heavy fire and some politicians have invited the army into the streets to fight crime -- an overture rejected flatly by the generals. Said one: "Our mission is to defend the fatherland against international communism . . . Not fight muggers."

In a more practical move, two of Rio's largest hotels, the Intercontinental and the neighboring Nacional, have pooled their resources to protect guests staying in their 1,200 suites. They now spend $30,000 a month on 36 security guards. Desk clerks at the Intercontinental routinely hand new guests their room keys with a multi-lingual card warning against leaving the hotel with valuables. Even so, a tourist in the area is robbed almost every day.

Rio's rising crime has not caused foreigners to cancel trips to Brazil, according to Miguel Colasuonno, president of Embratur, the state tourism agency.

"Unfortunately the experienced traveler knows things much worse than Brazilian criminality," he said recently.

With 5,000 miles of beaches, uniformly warm weather and exceptionally friendly people. Brazil constitutes one of the world's greatest potential tourist attractions. But Latin America's largest nation receives less than one percent of the world tourist trade. Last year Embratur spent only $4 million promoting Brazil -- mere pennies when compared to the $42 million spent by Mexico in 1979.

The major stumbling block for Americans has been high air fares. Embratur hopes to overcome this barrier with a $847 "Fly to Brazil" package, which includes hotels for a week and airfare on a triangular route -- New York-Manaus in the Amazon-Salvador on the Atlantic Coast -- New York.

Supported by hundreds of thousands of brochures and widespread newspaper and television advertising, Embratur officials hope this long-term campaign will seduce Americans into flying over the Carribean islands and into Brazil.

Until recently, almost all Brazilian travel posters features glistening beaches adorned with pouting girls in microscopic string bikinis. The new approach is different.

"I'm not selling beaches -- if Americans want beaches, they can go to North Carolina," said Francisco Ignacio Havas, director of international projects for Embratur. "I'm selling the Amazon jungle, historic cities, Brazilian culture, vatapa, candomble," he continued. (The last two items are the spicy food and spiritist cults of Salvador, capital of Brazil's African heritage.)

However, Brazil's beaches -- and the beautifully tanned bodies on them -- remain a great magnet to many Americans. Kathy Kohlhof, a Peace Corps volunteer posted in landlocked Paraguay, explained why she chose Rio for her vacation: "I wanted someplace where I could relax and sit on the beach -- I am from the Midwest and we don't have any beaches there."