KIICHI MIYAZAWA, the leading internationalist among Japan's politicians, is most likely to become the next prime minister of Japan. That's my prediction for the contest that is to take place at the end of October. It is also my hope. Decisions Japan must make as a key member of the global community have been piling up for the past two years, and the country needs an experienced hand at the helm, a leader who can make these decisions even if some of them are unpopular.Mr. Miyazawa is one of a handful of Japanese politicians with whom leaders of other countries feel they can really communicate. Helmut Schmidt, former chancellor of West Germany, has a pretty acerbic opinion of Japan's faceless leaders. He counts Miyazawa as one of Japan's few men of international economic and political stature. This is not only because of Miyazawa's fluency in English. It is because he is interested in and can hold his own in the thrust and parry of intellectual argument, in the ideas t hat move men and nations. He has been accused of being dilettantish, of being cautious and introspective rather than daring and outgoing; but his grasp of world affairs is sure, and, at 72, he knows that if he becomes prime minister he has not much time within which to make his mark. He has shown boldness before. When serving as finance minister three or four years ago, Miyazawa devised a far-reaching plan to recycle the debts of third-world nations. Its key features were incorporated into what later became known as the Brady plan (named for Treasury Secretary Nicholas Brady). TODAY the global community needs thinking on a much bolder and more creative scale to deal with the collapse of the Soviet economy, with the problems of Eastern Europe, with Latin American and African debt, with the restless energies of emergent East Asian nations, with the huge question mark posed by China, to say nothing of Middle East turmoil, world trade problems, the global environment, and population and migration pressures. Japanese bureaucrats are present in discussions involving many of these is sues. But in the absence of strong political leadership at home, their voices are heard only as after-thoughts by the movers and shakers of world opinion. Whether Miyazawa will indeed make himself a distinctive and effective voice within the global community remains to be seen. Although Japan has a small pool of talented younger politicians, none has Miyazawa's international stature or experience. Miyazawa is a nationalist; he will argue what he perceives to be Japan's national interests. But he is also an internationalist, because he can perceive and articulate the interests of the global community as a whole. The test, of course, will come when these two interests seem incompatible, as when Japan seeks to preserve a closed rice market even though it knows that free trade is the way to prosperity for all. When President Bush pleaded with Prime Minister Toshiki Kaifu to set a free trade example fo r the rest of the world by opening its rice market, Kaifu said he could not afford to squander his domestic political capital by giving way on rice. Kaifu was a popular but weak leader. Miyazawa will have to consider what priorities to set, knowing that what he gains in international acclaim he may lose in domestic support. Miyazawa should become prime minister because of his wide experience in international affairs. The irony is that if he does win the race, he will probably do so for a very Japanese reason - the argument that it is his turn. When Eisaku Sato quit the premiership in 1972, five candidates vied for the succession. Every single one of them became prime minister in turn, the last of them being Yasuhiro Nakasone. When Nakasone quit in 1987, there were three contenders - Noboru Takeshita, Shintaro Abe, and Miyazawa. Nakasone chose Takeshita, who would most likely have been succeeded by Abe, had not the Recruit political scandal intervened. Abe died this spring, and Miyazawa is the only surviving member of the trio. It's the kind of argument a Margaret Thatcher would laugh at, but in Japan it still has its resonance.