FIFTY years after Pearl Harbor, relations between the United States and Japan have reached another critical turning point.Since the end of World War II, the Pacific giants have been close allies bound by a common enemy and a vast network of trade ties. But with the end of the cold war, strains have developed that have put the relationship to a test. Adapting to new times need not be disruptive. As one State Department official notes, the US and Japan "share fundamental interests and values on most issues," and have far more to lose than gain if relations are allowed to deteriorate. But adapting the relationship will require major adjustments, both psychological and structural. If the transition is not managed skillfully and if growing antagonism over trade issues is not contained, relations could take a huge retrograde step. In the worst case, trade tensions could lead to a "yen-dominated free-trade bloc in Asia which would have a wall up around it toward the outside," says Edson Spencer, chairman of the Commission on US-Japanese Relations for the Twenty-First Century. "That would be a different kind of Pearl Harbor leading to a series of events that could lead to a breakdown of US-Japan relations." "It remains to be seen whether the US-Japan 'problem' is a prologue to estrangement or marks a shaking out period for a transformed alliance which enjoys the confidence of our respective publics," concludes a commission report issued last month. At both ends of the alliance, the collapse of the Soviet threat has prompted a rethinking of foreign policy priorities that could impinge on US-Japanese ties. In Washington, policymakers advocate more selective engagement abroad and closer attention to problems at home. One manifestation is the gradual drawdown of forward-based military positions in the Pacific, including the Philippines and South Korea. In Tokyo, meanwhile, policymakers debate how to play a more assertive role abroad without engendering political divisions in a country already distracted by financial scandals and discontent with soaring prices. "The question for Japan is, how can Japan play a more responsible role in the world ... and still continue to be Japan," says Stephen Bosworth, president of the US-Japan Foundation. "Decisions are now being made in the US and Japan that will shape the relationship for the next decade, if not the next 50 years," comments Philip Brenner, a professor of international relations at American University. President Bush has rescheduled a trip to Japan and three other Asian nations which was canceled earlier last month because of pressure to devote more attention to domestic affairs. Though official reaction to the cancellation was muted in Japan, Japanese leaders were clearly disappointed that the symbolic reaffirmation of close US-Japan ties will not take place before the Dec. 7 anniversary of Pearl Harbor. Mr. Bush will arrive in Japan for a three-day visit on Jan. 7. On Dec. 7 he will participate in ceremonies at Pearl Harbor, Hawaii. On the eve of the anniversary, 84 percent of Americans hold a friendly view of Japan, according to a Roper poll conducted for the American Enterprise Institute. Seventy-five percent believe that Pearl Harbor is "all in the past" and should not have bearing on US-Japan relations. But beneath the veneer of general support is widespread anger in the US, especially among American workers, over Japanese trade practices that have contributed to the US's $40 billion annual trade deficit with Japan. If the deficit is not reduced, the temptation for politicians to look for scapegoats could prove irresistible. "Now that the Soviet Union is no longer out there as a threat, politicians are likely to look for new people to blame for things that aren't going right," says Mr. Edson, speaking at a Johns Hopkins University forum on US-Japanese relations. Japan says that the main reason for the trade deficit is that high wages, poor workmanship, low savings, and high debts have cost the US its competitive edge. American critics respond that the US has been the victim of unfair Japanese trade practices that range from outright product exclusion - rice, for example - to nontraditional barriers. The latter include stringent product standards and collusion among Japanese manufacturers, financial institutions, and marketing firms that have had the effect of restricting imports. According to some estimates, such practices account for fully one-fourth of the US's trade deficit with Japan. "We have to have high-quality, well-serviced, well-marketed products adapted to Japanese tastes to succeed in the Japanese market," acknowledges Mark Van Fleet, director of Asia-Pacific affairs at the US Chamber of Commerce. "But even if we did all these things we would still have difficulty making inroads in areas of the Japanese market." "Being part of an international system where you gain the benefits of other countries' more open, hospitable [trading] system implies a responsibility on Japan's part to move toward a more open system," says Mr. Van Fleet. "While our so-called 'allies' avoid our taxes, rob Americans of their jobs and use their profits to buy much of America, they still depend on us for their costly defense," complains an evocative appeal issued last month by the "Made in the USA Foundation." Years of on-again, off-again trade talks between the two sides have done little to ease trade tensions. Economists worry that if Congress now gives in to protectionist pressures and if Japan is closed out of the economic blocs taking shape in Europe and North America, Japan and the rest of Asia could turn inward. Worried about those possibilities, 15 Pacific Rim nations - including the US and Canada - last month coalesced into a potentially powerful economic grouping, Asia Pacific Economic Cooperation (APEC). Any move to create an exclusive East Asian trading bloc would close US businesses out of some of the world's fastest growing markets. Since the end of World War II the US has carried the main burden of securing East Asia and the Pacific against Soviet expansion while Japan has hosted US military bases manned by 50,000 US troops. Threats to the region remain, including North Korea's nuclear ambitions. But the collapse of the Soviet Union has exposed ambivalence on both sides about the existing security relationship. On one hand, the US public is tired of what it sees as spending vast sums to keep the Pacific safe for Japanese trade. On the other hand, the unstated conviction lingers, both in the US and in Southeast Asia, that US troops are a barrier to a militarily resurgent Japan. For its part, the Japanese public is still reluctant to take on major defense obligations in the region, but is increasingly restive about having foreign troops on its soil. Japan's reluctance to be drawn into overseas commitments has been demonstrated by a long fight in parliament to liberalize inter- pretation of a constitutional prohibition against sending troops abroad to allow for Japan's participation in UN peacekeeping missions. As Japan's aversion to being a world player gradually diminishes, analysts say, more questions are likely to be asked about the usefulness of the US-Japan military alliance, especially as the US contemplates lowering its own military profile in the region. During a visit to Tokyo Nov. 11 Secretary of State James Baker III promoted Japanese participation in UN peacekeeping, which Japan's lower house of parliament approved on Dec. 3. He also urged Japan to do more to prod global trade talks now under way in Uruguay, aimed at lowering worldwide tariff barriers. Asia scholars note the irony that even as Japan hesitates on the issue of a wider security role, it is sharpening the economic tools, including foreign aid and direct investment, to assume wider economic and eventual political influence in the region. Barely six years ago, for example, the US had more foreign investment in Thailand than Japan, explains Kenneth Pyle, professor of East Asian studies at the University of Washington. Now Japan dominates, with 25 times more foreign aid than the US, while a Japanese factory is opening in Thailand almost every three days. Dr. Pyle says the new Japanese role in Asia could test the US's commitment to provide security for the region even as it relinquishes its economic leadership to the Japanese.