VANG VIENG, Laos — Drunk Brits leer at passing female tourists. A Western tourist gets in a public shouting match with her guide.

And stoned backpackers lounge gape-mouthed in cafes, eyes glued to televisions playing looping reruns of "Friends" and "Family Guy."

Welcome to Vang Vieng, one of Laos' premier tourist destinations. Just don't call it "unspoiled."

As this Southeast Asian country opens its doors to tourism, it's facing a classic conundrum. The poor, underdeveloped country desperately wants to earn tourist dollars. But it also wants to preserve its conservative, traditional ways. Doing both may be impossible.

"It's hard to keep the balance between development and the preservation of tradition and local culture," said Thavipheth Oula, an official at the Lao National Tourism Administration, in an email. "The issue is how we can keep Lao identity while the number of tourist arrivals increases."

In the 1960s, America waged a "secret war" here against the Pathet Lao communists. Now, the country that once crawled with spooks has been invaded by tourists.

Annual tourist arrivals have tripled in 10 years, from half a million in 1998 to 1.7 million in 2008, according to numbers from Laos' tourism authority. Tourism now brings in $275 million in annual revenue, up from $80 million in 1998, making it Laos' second biggest money-maker after mining.

The key draws are the capital, Vientiane, and the temple-studded World Heritage Site, Luang Prabang. The latter's development is regulated — for example, with strict building codes. Well-preserved wats crowd up against hip, new French-Lao fusion restaurants and bars.

But Vang Vieng has no such restrictions. Instead, it's carved out a niche as a mandatory stop on the backpacker trail through Southeast Asia. And it caters to 20-something hedonists with scores of cafes, bars and riverside debauchery, making it something of a "lost city of sin" in the heart of Laos.

Vang Vieng's natural beauty is breathtaking: It sits on the Nam Song River amid jagged karst mountains.

The obligatory activity here is inner-tubing down the river. Tourists crowd onto trucks that drive them to a spot upriver from the city. By the launch site, hordes of shirtless and bikini-clad Western tourists gyrate to deafening techno music, as others hurtle into the river from rickety wooden platforms three stories high. As these two YouTube videos illustrate, it's like the underground party scene from a "Matrix" movie.

Enterprising locals have built riverside bars hawking the national pride, "Beerlao," and jerry-rigged flywires over the river. Lao touts tempt passing inner-tubers by throwing lines at them; if you're thirsty you just grab on and they pull you in.

Such attractions are a big draw for younger tourists, in particular. But they have some wondering whether Vang Vieng has lost its soul.

"Each time a young Australian woman strolls down the street in a bikini, a bearded American smokes a joint on a guesthouse terrace, or a group of Koreans tumbles drunkenly out of a restaurant, it saps a little more of the essence of a town like Vang Vieng," said Brett Dakin, the author of "Another Quiet American," a chronicle of two years in Laos working for the tourist authority.

"Tourism has contributed a great deal to communities like these: rising incomes and higher standards of living," Dakin wrote in an email. "But there is a sense that something has been lost in the process."

There's no easy solution to the problem. Oula, of the tourism authority, says restrictions on young foreign backpackers would backfire by taking away much-needed income from the local Lao who run guesthouses, restaurants and other tourist businesses.

Instead, the authority is pinning its hopes on "awareness programs" for tourists and locals. Such programs will "ask tourists to respect and strictly follow the rules, regulations, tradition and cultures of the Lao people," Oula said.

"At the same time, [we should] educate local people to maintain the Lao identity, way of life, tradition and culture and not imitate tourist behavior."

For Dakin, a little sensitivity could go a long way. There are some basics in Laos: dress conservatively (that means no bikinis and shirtless-ness in public, a suggestion posted clearly in English throughout Vang Vieng). Take off your shoes indoors. And try not to poke your camera in the monks' faces at the traditional morning alms-giving in Luang Prabang.

"It's not hard to travel responsibly in Laos, it just requires a little thought, and perhaps above all the ability to empathize," said Dakin. "Would you want your visitors acting this way in your hometown?"