YOU WON'T get a hint of it from the tour brochures or government giveaway literature, but the Emerald Buddha isn't the only thing that's whooping up tourist business for Thailand.

More than 30 years after the Japanese introduced massage parlors during their World War II occupation and a decade after American Vietnam forces' R & R requirements redefined the concept of bar girls, Bangkok - the nation's sprawling, boomtownish capital - has become Asia's sex supermarket. It's known as the No. 1 place to go for quantity, quality and low prices.

For a few newcomers, the story seeped through slowly. The first glimmer came as they sat in a shared taxi outside the arrivals halls of Bangkok's airport, moist body crushed next to moist body, waiting in the steamy night for the driver to fill one last pair of places.

Then there they were, two flushed, baby-faced American males in the pearly pink dawn of their 20s, twitching like disco dancers just before the music starts.

"The Grace Hotel," one half-breathed, half-blurted as they climbed in.

The driver hesitated "The Grace Hotel?" he repeated. The two men nodded yes. The driver tried again.

"You sure?"

They were sure.

Naturally they were sure, says the proud and pleased owner of the hotel, Chalerm Kaukham. Most people who go to the Grace are quite sure. Furthermore, it's a good idea to have reservations, because the hotel operates at about 80 percent capacity year-round, which means sellouts are a frequent event.

This kind of popularity for a place that looks and charges like a slightly worn budget motel? In a city where you can do lots better for not much more? Yes, indeed - but then the others don't have the Grace's coffee shop.

Empty, it doesn't seem like much. However, it's hardly ever empty. After about 8 p.m. it becomes one of Bangkok's foremost chambers of commerce, and night after night, it bulges with 200 or more mostly self-employed businesswomen who pile their purses one on top of the other, roll up a lot more than their sleeves and sell, sell, sell. The music blares, the entrepneurs chatter and jiggle, the foreign buyers let their hands and eyes roam over the merchandise. Even with the air-conditioning operating at top level, the atmosphere is decidely torrid.

But then - hello there! - so is Bangkok. A surprised American woman tourist walking in the middle of the day from Sheraton hotel to a restaurant just behind Patpong Road reported being stopped es route by three "advertising men." One offered information on male prostitutes, one was pushing a lesbian sex show, one a lesbian massage parlor. The last even proffered pictures.

Patpong is neither as large nor a raucous as many big city sex sections, but its impact is great by virtue of being in the heart of the tourist belt. The action is technically illegal - and for some it's like "fishing in an unclean aquarium" - the area offers everything that anyone but the Marquis de Sade might want.

The gay scene, for instance, is quite large and includes numerous transvestites. In fact, according to a long-time foreign resident, at one Bangkok beauty contest it was announced that only one of the contestants was female ("See if you pick her!" challenged the emcee).

"Like in Copenhagen, like in Stockholm, like in Amsterdam, life is wonderful!" enthuses the Grace's Chalerm, "Many men come every year now, especially from Germany."

The Germans and other nothern Europeans most often arrive the first time by chartered plane. Other males also come in large and small groups from Japan, Hong Kong and Australia. Considering the distance, and the availability of similar activities closer to home, why?

"That's easy," says a resident male chauvinist American. "The girls here are less demanding, more un-tight and have lots of imagination. Thai girls are what girls should be - feminine, graceful, compliant. Actually, though, they do have tremendous tempers if they're deceived. You can hear lots of tales of what's been done with knives."

Somehow, though, Bangkok's "working women" also seem to inspire more tolerance than censure among the locals as well as foreigners.

"It's a great shame to the Thai people," says a secretary, a pained look crossing her delicately pretty face, "but what can they do? Those girls are from up-country, from the rice paddies. There they could make $110 a month; now they make $400."

What their families and friends in the rice paddies don't know doesn't hurt, either. Many take early retirement from the Bangkok scene and go back home as soon as they've saved some money. Others get "lucky" and marry their tourist customers.

But Thailand is a poor country, and so tourism based on the sale of the four S's - sand, sun, sea and sex - is spreading rather than shrinking, in the new, Miami-style beach resorts as well as the capital. And Bangkok (for a variety of reasons, to be sure) has wound up looking even more sluttish than the toughest girls from the Grace. Its jammed, almost-treeless streets and ugly, thoughtless buildings make the year-round heat and humidity more oppressive than ever. The scene also transforms into poor jokes the Thais' sentimental, oft-repeated claim to a kinship with easy, harmonious living.

That spirit and examples of the country's soft, shimmering beauty are still available. There's the north, in an around Chiang Mai for instance, where it's now possible to visit the once remote hill tribes. One can see as well the Khmer ruins in Surin, where the annual Elephant Roundup Festival takes place Nov. 18-19 at the beginning of Thailand's best weather period, and take in the still-sleeping beauty beaches of the south coast.

In "Thailand: A Complete Guide," author William Duncan even makes a suggestion for "low budget travelers" that might well be copied by anyone not entirely captivated by the sex scene.

"In Bangkok," he writes, "See the Grand Palace, several wat (Buddhist temples), the Weekend Market, classifical dancing at the National Theater, the National Museum (admission free on Sundays), and then get away into the provinces."

Duncan does not speak with forked tongue. Those are the eye-poppers - plus, of course, the Grace Hotel's incredible coffee shop.