While the People's Republic of China is just beginning to throw open its doors to foreign tourists, business continues as usual just across the border in Hong Kong, the bustling, tourist-saturated land that is grappling with the problem of being too successful in attracting visitors.

Hong Kong, the British colony known for its cut-rate prices on watches and jewelry, its 24-hour handmade suits, its beautiful "dragon ladies" and its spectacular harbor, has become a victim of its own success.

Last year, for the first time, Hong Kong attracted more than 2 million tourists and projections for this year are that at least 2.2 million tourists will jam the narrow alleyways and broad avenues of Hong Kong and neighboring Kowloon.

Business is so good, in fact, that last year there were 25 days when every one of Hong Kong and Kowloon's 14,168 hotel rooms were filled, and another 50 days when it was nearly impossible to find a place to sleep. The average occupancy rate for Hong Kong hotels last year was 89 percent, an astronomical figure that makes hoteliers in other parts of the world insanely jealous. This year, the average occupancy rate is projected to be 92 percent. And, since only 400 new rooms are scheduled to be completed in 1979, and 3,000 by the end of 1980, there literally may soon be no room at the inn.

Added to all this success is the possibility that the opening of China will further increase Hong Kong's tourist trade, since tourists who have not made prior arrangements and decide to try while in this area must pause in Hong Kong to apply for a visa, a process that takes at least four or five days. That means more and more people will need rooms as they wait for the exotic adventure into the People's Republic.

"the opening of China will have an immense effect on us," believes Graham Hornel, public relations director for the Hong Kong Tourist Association. "it will put us back in the role of stopover destination, which means even more tourist growth. If growth hits as it might, it could be bloody embarassing since we just don't have enough hotel rooms. Even without the China opening, we forecast an 11 percent increase in traffic from the United States for this year. We are going to have a real image and goodwill problem ahead of us."

Hornel also cited the new, lower airfares to the Far East as a major factor in the increasing numbers of tourists visiting Hong Kong.

"this is a new phenomena here - the 'backpack' traveler," he said. "we simply have no facilities at all for people like this and, once they arrive, we're not too sure what to do with them."

So what is Hong Kong doing to survive this abundance of riches, besides constructing new hotels? For one thing, it is trying to appeal to a particular type of tourist, one who will stay longer and spend more money.

"basically we want the up-scale visitor who will spend more on the economic side. Average expenditure by visitors is more important to us than numbers of tourists," Hornel said.

Last year, for example, the average American visitor spent 2,273 Hong Kong dollars (about $530 U. S.) during his stay in the colony. But visitors from Japan, Australia and Europe had a higher average expenditure than did visitors from the United States. No longer the big spenders, we Americans.

Hong Kong is also hoping to attract more conventions and, as part of this effort, will have three new convention centers ready by 1982. It is also pushing special interest tours, whose members tend to stay in the better hotels, remain in the colony longer and spend more money.

Just why is Hong Kong so successful when so many nations - especially in Asia - are desperately trying to attract tourists? Why were 55 percent of last year's tourists repeat visitors, back for a second, or a third, or a 100th time? There are a number of reasons:

Shopping. Despite a rise in prices, Hong Kong is still a shopper's paradise.

English. Taking English is mandatory in all Hong Kong schools and most locals have at least a working knowledge of the language. Roads signs and shops signs are bilingual, and it's not hard to find you way around if you have a good map.

Mystery. Before the opening of Mainlan China, Hong Kong was as close as you could get to experiencing a Chinese culture. And the nystery lingers on.

Facilities. Hong Kong was made for tourists and has some of the finest hotels in the world waiting to pamper even the most particular.

Food. There are more than 4,ooo restaurants in Hong Kong and Kowloon serving some of the finest cuisine in the world.

Sex. Although much of it has gone by the way, now that Vietnamese conflict is over and American soldiers are no longer using Hong Kong for R&R holidays, you can still rent an "escort" for the night at any number of establishments.

Transportation. Mass transportation - from the Star Ferry cruising between Kowloon and Hong Kong, the double-decker tram, to the jammed buses, to the massive fleets of taxis - is both good and cheap. And a new subway system is being added to make it even easier to ger around the country.

Relaxation. Despite the bustling core Hong Kong, it is only a 10-minute drive to the south side of the island, with its beautiful beaches and quiet small hotels; and a trip into the new territories, which make up 77 percent of Hong Kong's area, shows you that most of the colony is still relatively rural.

Of all of these attractions shopping is by far the biggest. According to a Hong Kong Tourist Association survey, 63 percent of all tourist expenditure last years went to shopping. But it's not the bargain it used to be. CAPTION: Picture, no caption