Japan, striving to open its doors to the world, is appalled to find it has let in AIDS.

The country's first confirmed case of the disease was announced March 22. Since then, 10 more have been found. Already, six of the patients have died.

The number of victims so far is small, but officials at the Japanese National Institute of Health have estimated that as many as 7,000 Japanese may be carriers of the virus that causes AIDS.

The Japanese government followed the lead of other AIDS-threatened countries last week and banned blood donations by homosexuals, drug users and other high-risk groups. Earlier, it imposed controls on imported blood plasmas, some of which had been found to be contaminated with the virus.

With AIDS has come public fear. "We in Japan can't rest assured thinking it is a matter that only concerns others," a front-page columnist in the Asahi Shimbun newspaper wrote earlier last week. "Unless a small fire is put out speedily when it is still small, it will turn into a big one."

Homosexuals accounted for six of the 11 victims in Japan. The rest were hemophiliacs.

Word of the disease has cut down the crowds in Tokyo bars and bathhouses catering to gays, according to Bungaku Ito, editor of a Japanese magazine for homosexuals.

Prevention and education efforts are complicated by the fact that gays still form very much an underground society in Japan. A sizable foreign gay community is found in Japan today as well, and it is blamed by health officials here for establishing the virus among Japanese sexual partners.

In July, 85 Japanese and 20 foreign gays presented themselves for voluntary AIDS checks conducted by a Tokyo university. Three of the Japanese and two of the foreigners were found to be virus carriers.

Meanwhile, sample testing has indicated that about 30 percent of the country's 5,000 to 7,000 hemophiliacs are virus carriers, apparently due to infection by foreign blood plasma, most of which comes from the United States.

The government is now working with 574 hospitals around Japan to identify new cases and inform the victims about the disease and the risk of spreading it through sexual contact. It is also conducting preventive education, targeted mainly at gays and people who receive blood transfusions.

Takashi Kitamura, AIDS specialist at the National Institute of Health, is pushing for an aggressive testing program and identification of risk groups. "There's a slight chance that if we hold things where they are now, Japan will be safe from AIDS," he said.

Some people feel the government is not ready to act on that scale, however. Magazine editor Ito maintains that officials underestimate the scope of gay sexual activity in Japan and the potential for further infection. "They should come to the hotels and saunas and see for themselves," he said.

Japan's widespread prostitution and high rates of extramarital sex would seem to make rapid transmission of the disease into the population at large likely if the virus were to become established outside the known high-risk groups.

A spokesman for the Ministry of Health and Welfare declined to say whether it views AIDS as a threat to the Japanese population at large. "For the present we think it's necessary for people to know what AIDS is," he said. "Then they can decide what to do."