A few months ago, not far from this picturesque village overlooking the mysterious blue waters of Lake Atitlan, a dozen foreign tourists negotiating the price of Guatemalan Indian weavings suddenly found themselves surrounded by a band of armed men.

"Don't worry, we are not bandits. We are revoluntionaries," the leader of the band told the terrified tourists. Leaning his German-made G-3 semi-automatic rifle next to a fountain in the village square, the guerrilla produced a proclamation, which he read aloud in Spanish to villagers and tourists alike.

"We are engaged in a war with Guatemala's oppressive government," he shouted. "We seek justice, liberty and land."

The harangue lasted about an hour. The tourists, meanwhile, were frantically hiding dollars, credit cards and Guatemalan quetzales inside shirts, braasieres and secret pockets.

"We wish you no harm," the guerrilla leader concluded. "But we ask you to take our message to the outside world. Please tell others what we are fighting for here."

With that, the guerrillas melted into the green jungle hills and volcanoes that surround this magic lake of the ancient Mayas.

It was not the first time such an incident has happened to tourists. And it probably won't be the last.

Unfortunately for Guatemala, such stories have had a disastrous impact on tourism -- this Ohio-sized nation's No. 2 industry. So far in 1981, tourism is down almost 40 percent, according to government figures.

Hotel occupancy, which two years ago averaged 70 to 80 percent, is now running at about 30 percent, according to one European embassy's attache.

But fear of Guatemala's ever-increasing guerrilla uprising (at least four groups totaling some 5,000 guerrillas are currently at war with the three-year-old military regime of President Romeo Lucas Garcia) is not the only thing discouraging tourists from coming to this singularly beautiful Central American country. An inflation rate nudging 20 percent has also had a dampening effect on Guatemala's $250-million-a-year tourist industry.

"The American tourists seem to have disappeared faster than the others," said Jose Amaya, a Guatemalan tour guide, "The Germans, French and Swiss still seem to be coming like before."

Two reasons for that may be America's physical proximity to Guatemala, which enables Americans to keep better informed of events, and the violent uprising in El Salvador just next door that has received wide coverage in American newspapers and on television.

"A lot of Americans come here and the first thing they ask is 'Is it safe?'" said Amaya, sipping rich Guatemalan coffee in the patio of a small cantina in this tiny fishing village. "I tell them, 'Yes it is safe if you are not stupid.'"

"The problem with Guatemala quite simply is that you never know when or where the violence may happen," he said. "It could be in downtown Guatemala City . . an assassination in broad daylight of some police or army official. Or it could be here in this village if guerrillas decide to attack an army garrison. That is the nature of guerrilla warfare."

For its part, the Guatemalan government has spent lots of time and money trying to convince the world that Guatemala is still a safe and economical travel destination.

Mario Echeverria Trigueros, president of the Guatemalan Chamber of Commerce, has repeatedly told such groups as the American Chamber of Commerce and the American Society of Travel Agents that tourists are perfectly safe in Guatemala.

Indeed, there are still no travel advisories from the U.S. State Department, though a visit to the American Embassy on Avenida Reforma, 7-01 Zone 10, will net you some sound advice about not venturing too deep into the war-torn regions of the west and northwest.

In Guatemala City itself, however, the impact of the uprising on this nation of 7.2 million is evident. Nightlife has all but disappeared. Restaurants, discos and bars are depressingly empty.

The blame for this can be placed mainly on Guatemala's escuadrones de muerte (death squards), which operate with seeming impunity throughout the city. These squads of armed men prowl the streets at night and have carte blanche to stop anybody on suspicion or question anybody who may have made comments too liberal for their taste.

According to Amnesty International, Guatemala's death squads have been responsible for the murder of 20,000 people in the last 15 years. One foreign embassy official says at least 500 persons have already died as a result of political terrorism this year, and the death squads were probably responsible for the deaths of some 3,000 persons in 1980.

"Violence has polarized this country," said one American resident of Guatemala City. "People are afraid to go out at night anymore. The city is gradually dying, losing its vigor, its spirit."

If Guatemala City's spirit dies by night, it still thrives by day. The city's famous mercadoes, or markets, which abound with handmade textiles, pottery, jewelry, baskets, blankets, reed mats and wood carvings, will keep any tourist's mind off revolution.

At the Handicrafts Market near the railroad station you will find a bargain-hunter's paradise. But if you shop here be prepared to bargain -- you can usually get away with paying half or a third of the asking price of an item if you are willing to haggle.

At the nearby Terminal Market near the bus station, colorfully clad Indian men and women arrive with huge bundles of merchandise on their back. Here you will find everything from knives and machetes to food and hardware. You will smell the delightful aroma of Indian foods cooking over open fires: stuffed peppers, pancha de papas, chuchitos, mole de platano, and tamalitos de elote.

Despire its political problems, Guatemala still has the best variety of hotels in Central America.

Compared to Mexico, which borders it on the north, Guatemala is indeed a bargain. Nowhere is this more evident than when it comes to dining. Not only does Guatemala have Central America's best hotels, it also has its best restaurants. And they are still inexpensive by American or Mexican standards.

For example, a meal at a deluxe restaurant will cost $8 to $15. But at moderate restaurants, where the food and ambience are hardly any different, excellent multi-course meals can be had for $5 to $8 a person.