Nepal PLANS ARE AFOOT to turn Katmandu, until recently a city forbidden to all but the most privileged of foreigners, into what an official of an American gambling company has called "the Las Vegas of South Asia."

A Large casino in a hotel basement is pulling in tens of thousand of dollars from tourists, prostitutes from Thailand are operating freely in at least one part of the city, and the Nepalese government is now being asked to allow the casino operators to introduce "dancing girls, high class entertainment and good, Vegas-type "fun" for visitors.

What makes the scheme unusually interesting is that the Nepalese royal family - Nepal is the world's only Hindu kingdom - has adopted a moderately enthusiastic attitude toward som aspects of the project. According to H. O. Kim, a South Korean with the U.S. owned casino firm. "They get a piece of the action, and they are starting to like it. They were a bit hestitant at first, but the profits from the casino - of which the government gets 40 per cent - seem to be proving very tempting."

While the Thai prostitutes established in one brothel appear to be working on a free-lance basis, the gambling and enterainment operation is the brainchild of an American, Richard Tuttle, who is the managing director of a Hong Kong based organization, Continental Resorts Ltd. Tuttle's visiting cards give his address as 200 South Virginia, Reno, New., though he spends a considerable amount of time each year in both Nepal and Hong Kong. He was not in Nepal this week.

KIM, HIS DEPUTY, was happy to outline the company's plans for Katmandu. Sitting in a small room at the rear of the Smoky, noisy Casino Nepal. Kim, impeccably dressed in light grey cashmere blazer, said: "Do you realize that there isn't a single gambling operation of any size between Tehran and Singapore? Mr. Tuttle believes that Indians - as weelas Western tourists - who want to enjoy themselves in this way, we should provide a service for them here.

"Of course, you expect some reluctance in a Hindu country. They are very conservative. But they badly need foreign exchange, and it is beginning to look as though they will let Mr. Tuttle expand Continental Resorts' operations provided we can work out the kind of percentage of the gross that's best for them to take and us to afford."

The Western embassies in Katmandu, which are concerned at Nepal's important position in the international traffic of drugs, view the development of the casino - taken over by Tuttle 18 months ago from a homegrown exceptionally amateur organi zation, with some disquiet. They stress that, despite rumors of peripheral involvement of U.S. organized crime in some of the more colorful activities, no suspicion at all is to be attached to Continental Resorts.

"We just keep an eye on these things," said one diplomat.

THE ATTITUDE OF Nepal's King Birendra and other members of the royal fnmily dismays members of the banned opposition political parties. Nepal is, in effect, ruled by a nearabsolute monarchy, although a partyless form of government handles the machinery of administration.

The family is already heavuly financially involved in hotels and travel agencies - the Soaltee Oberoi, where the casino is part owned by the kings's uncle. Prince Himalaya; the Annapurna Hotel and Katmandu's premier travel agency, Yeti Travels, are also royally owned. Kim said the family has given its blessing to the expansion of the gambling and night life activities planned by Continental Resorts.

"There is something very offensive in the king's tolerance of this kind of activity," said a member of the banned Nepali Congress Party, a politician who, like most critics of the government prefers to remain anonymous.

"The majority of our people are very simple, conservative and religious and they find this kind of thing foreign to all that they thought our royal family stood for. We would hate to see Katmandu turned into something like Las Vegas. It would make people very unhappy."

AT THE CASINO, however, there was no sign of unhappiness, perhaps because of notices outside prohibition Nepalese citizens from entering. Although a sezeble number of American and West German tourists were playing black jack, roulette and craps in the small hours of the morning - the majority of players were Indians.

"The average take from an Indian is about 400 rupees (about $50) a night," Kim said. "We arrange package tour for them from Culcutta and Dehli, and if we're lucky they just stand at the one-armed bandits hour after hour. If they make money, they are free to take it home with them to India, of course. It's a great temptation for them."

The several Thai prostitutes, who have set up shop in another, smaller hotel in town, are almost wholly patronized by Westerners, it is understood, and on the road from the airport was one further sign of the influence of the world's fleshpots: Beside a Tibetan wool dealer's shop was a small yellow sign, "Message, one flight up, this way." A visitor from Reno would feel quite at home in Katmandu.