TOKYO'S reported decision to resume aid to Cambodia and Vietnam next year is another indication of Japan's growing sense of independence in matters of foreign policy. But Tokyo is rubbing up against a longtime United States policy discouraging aid to Indochina."We know it's a delicate situation with the US," says a Foreign Ministry official. He declines to confirm widely believed press reports about the resumption of aid to Cambodia. Foreign Minister Taro Nakayama is expected to announce the plan at the signing of a Cambodian peace agreement in Paris Oct. 23. Japan halted aid to Cambodia in 1973, and has withheld aid to Vietnam since its 1978 invasion of Cambodia. Over the last three years Japan has sent an average of $9 billion abroad each year. The Japanese are now embarked on a five-year plan that aims for a total of $50 billion by fiscal 1992. Japan's overseas development assistance (ODA) programs have avoided political criteria and have emphasized self-help for its recipients. But this approach has prompted criticism that Japan uses aid to meet its economic goals. "There is a difference in philosophy ... between Japan and Western countries," explains Robert Orr, director of Stanford University's Japan Center. "In line with missionary beliefs, Western countries focus on basic human needs, whereas Japan stresses self-help of the recipients and expands the definition of aid to include assisting the country's infrastructure through economic cooperation." But a poll taken by Japan's Economic Planning Agency shows Tokyo's goals are not well understood abroad. Recognizing that its motives are misunderstood, Tokyo proposed new criteria for ODA earlier this year. Japan now examines how much the recipient country spends on its military, whether it has developed and produced weapons of mass destruction, its level of weapons imports and exports, and whether it has promoted democracy. But the application of the principles is still delicate in practice. "We have notified recipient countries about the principles, but it cannot be treated as a rule of thumb," says Yasuaki Tanizaki, the chief of the Economic Cooperations Policy Development Bureau in the Foreign Ministry. "We have to look at individual countries with respect to their roles in regional stability." But Kazuo Sumi, a Yokohama Municipal University professor, says the government is not serious about the four principles. "It is only interested in how to increase the dollar amount to meet the five-year plan."