The good old days of enjoying Japan's unique pleasures inexpensiverly are gone with the low yen, but the adventurous traveler can still make the tour here without risking insolvency and debt.

It takes careful advance planning, patience, and a willingness to forsake some accustomed frills. One new lodging-house program offers some of the old travel bargains for the tourists who can give up Western-style beds and beef and accept in their place a genuine touch of Japanese living.

Only the truly affluent can afford to do it the old way, meandering from one plush Western hotel to another in Tokyo or Kyoto or following the trial of shrines and temples by staying in handsome turral resorts. For that kind of tourist, Japan is now the land of $2 cups of coffee and $40 steaks.

Because of the rising value of th yen, the America dollar buys about a third less here than it did two years ago. For the past few months the exchange rate has been stabilized at roughly 200 yen to the dollar and the signs are tht it will stay there.

The result has been a sizable decline in the number of American toursits visiting japan and a shift in Asian tourism to the cheaper countries to the south. In the first 10 months of last year, the number of American visitors declined about 8 percent from the same period in 1977. At the same time, according to Japan's National Tourist Organization, American trraffic into Hong Kong, Taiwan, Thailand and Singapore was increasing.

Japan is also facing competition for the toursit's dollar from China, which is this seasonhs fashionableplace to have been in Asia. the Chinese government has opened up that country to many tour groups and the relative inexpensivensess of hotels and food ther make it a bargain of prices alone.

Japan's travel offerings are well-developed and familiar to foreign tourists by comparison, observes Hiroshi Ozawa, assistant general manager of the foreign tourist department of the Japan Travel Bureau. "From that point of view, it is difficult to find something extraordinarily new in Japan," Ozawa says. "So to compete with a new and fresh market such as China today is hard."

Getting to Japan is half the problem. Airline rates across the Pacific have not yet followed the way of transatlantic rates and the cheap fare is nonexistent. There have been proposals to cut the rates by as much as 35 percent, but the negotiations are deadlokced. Japan restricts the number of chater flights that can land at its major airports, and until the protracted U.S. Japan airline route negotiations are concluded the charter limits will probably be insisted upon. The one-way individual fare from San Francisco to Tokyo is $743, but packages can bring the price down.

Surveys by Japan's tourist officals have recorded mounting dissatisfaction with the high hotel and food prices. Many visitors reported they had to cut their tours short to save money and has reduced their spending on shopping and amusements. Last year, 90 percent of the foreign visitors complained in government surveys that prices in Japan were either "high" or "very high." Three years earlier, only l0 percent had registered such complaints.

The complaints and a spreading fear that Japan will be priced out of Western tourism have prompted both the government and hotels to plan costsaving measures, but the First-class way of travel remains expensive. For example, Tokyo's chic Hotel Okura has decided not to raise its room rates this year as a gesture to foreign tourists. But a double room still costs$77 in American currency and the restaurant prices are almost our of sight.

As a result, the Westerner won't have much trouble finding rooms if he can pay for them. For this spring season, the hotels are only about 50 percent booked. And that includes many travel agents' advance reservations, which eventually wil be canceled.

One traditional Japanese bargain has been opended to foreigners. For years, Japanese who wanted to see their own country on the cheap have stayed at "Minshuku," or People's Lodges. These are in private or other prominent resort areas. This year the Japanese National Tourist Organization is helping to open a number of them up as "international Minshuku," hoping they'll appeal to Westerners whose dollars won't go very far in the usual places.

The charge is $17 per person each night and includes two Japanese meals. Each house is clean and well-equipped and many offer at least one Western toilet. Sponsors also try to assure the avilablitity of at least one English-speaking person who can help the tourist over the language rough spots. The sleeping arrangements are strictly Japaese -- a mattress is placed on the tatami-matted floor and the customer packs away his own bedding every morning.

In exchange for the inconveniences, the visitor gets a rather vivid exposure to Japanese family life and, if he's lucky, manages to absorb a lot of local culture. The lodging house owner is frequently a resident sage with a wealth of knowledge about local folklore. There's one in Takayama, an old mountain village in central Japan, where guests learn how to make the popular straw dolls. In Kyoto, the ancient capital, one can taste the atmosphere of Zen Buddhism by staying in a temple. (Information of the "International Minshuku" is available from the Japan National Tourist Office, 45 Rockefeller Plaza, New Yeork, N.Y., 10020).

There are also some moderately priced, Western-style hotels and Japanese inns operating in Japan, but one will need a guidebook to find them. Or one can consult a list of such accommodations provided by the Ministry of Transport's tourist bureau. There are also lists of moderately priced restaurants which offer Western, Japanese and Chinese food at a maximun of $17.50 per person, including tax and service charges. There are 145 restaurants listed now and they are guaranteed to have at least one English-speaking waiter. The lists are avilable in the government tourist offices in Tokyo and in the new international airport in Narita.

Bacause of the language difficulties, many American visitors who normally spurn tour groups abandon their prejudices and seek out guided bus tours in Japan. There are one-day tours from Tokyo hotles at reasonable prices -- one village tour costs only $35 for bus service and lunch. Longer cross-country tours are available for trips to the scenic old capitals of Kyoto and Nara.