China's economic modernization and Japan's political coming-of-age are among the most significant themes of the remaining years of this century. The shape of the world in the 1990s is going to be decisively influenced by the answers to two questions:
First, will China hold to the course of modernization through cooperation with the West, as espoused by senior leader Deng Xiaoping, and will this course succeed?
Second, will Japan use the economic great-power status it has already achieved as a springboard to full political participation in Western decisionmaking and in the affairs of the wider global community?
At this moment, United States Defense Secretary Caspar Weinberger is wielding chopsticks in Peking as the guest of a leadership bent on improving relations with Washington while stressing independence of both superpowers.
Mr. Weinberger is in China because the Reagan White House, in its global confrontation with the Soviet Union, has come to see the value of a friendly, if non-allied, China. Peking's shrewd leaders are certain to rebuff any effort by their exuberant guest to line them up more explicitly with Washington against Moscow.
Indeed, it is not necessary for them to line up with Washington in order to affect fundamentally the global balance of power by the end of this century. For China's modernization, if it succeeds, will bring into the world power equation a nation of more than a billion people which already has the atom bomb, and which will have moved from the age of bicycles and pigs in wheelbarrows to one of put-putting motorcycle-sized tractors and imperiously trumpeting minitrucks.
Successful modernization will mean an income of perhaps $800 per head (compared to roughly $200 per head now). That is a very modest sum. But multiplied more than a billion times, it means economic power sufficient to profoundly influence the balance of superpower relations.
Meanwhile, in Japan, a forthright prime minister, Yasuhiro Nakasone, is awaiting an official visit by his friend Ronald Reagan to Tokyo early in November. Mr. Nakasone is the first Japanese prime minister to put himself on a ''Ron-Yasu'' first-name basis with an American president.
Neither a politically assertive Japan nor an economically resurgent China is assured of success within this century. Yet movement in this direction is already taking place. If it gathers momentum, world power - hitherto concentrated in North America and Europe - is likely to include a new pole centered in Asia.
Japan's more active participation in the political aspects of the Western alliance widens the circle of Western decisionmaking, as exemplified by Mr. Nakasone's forceful support for President Reagan on the SS-20 issue at the Williamsburg summit in May 1983. It also brings into that circle a member that many Europeans and Americans still consider a kind of exotic hybrid.
This hybrid partner Japan is the first non-Western nation to reach Western living standards. Its gross national product is the third largest in the world, outranked only by that of the US and of the Soviet Union.
Japan is also the first non-Western nation to have achieved economic success within the context of a highly competitive free enterprise economy and of a pluralistic parliamentary democracy. At the same time Japan is an Asian country, in which the structure of corporate management and of relations between capital and labor are more like that of a society within a traditional rice-growing village, where farmers must cooperate to survive, than the classical capitalist jungle.
At one time Westerners regarded Japan as a kind of star pupil. Now the former pupil is demanding a seat for itself at the table of Western decisionmaking. Meanwhile its lopsided economic prowess is accompanied by a military defensive capability so modest as to rouse the ire of American congressmen. Europeans and Americans alike tend to perceive Japan's growing economic aid as ungenerous, its treatment of Vietnamese refugees as uncharitable, its insistence on catching whales as uncivilized.
Japan's stance with regard to the South Korean airliner incident Sept. 1 may have improved these perceptions somewhat. Premier Nakasone reacted strongly to the Soviet downing of an unarmed civilian plane with 269 persons aboard, calling it a ''barbarous act.''
A single incident, however dramatic, is unlikely to reverse perceptions nurtured over many years unless the Japanese follow it up with a whole series of actions putting them much more visibly within the Western camp.
Yet, visible or not, the fundamental fact about Japan today is that it is Washington's most important ally in the Pacific. US Ambassador Mike Mansfield goes so far as to dub the Japanese-American relationship ''the most important in the world - bar none.''
Honorary Westerner or not, Japan has cast its lot with the West, and this basic strategic decision is not likely to be reversed by irritations, however great, over trade or over Japan's proper role within the alliance.
China is a different story. China makes no pretense of being capitalist, or democratic in the Western sense. China is communist.
China's relations with the US have had their ups and downs since 1971, when Richard Nixon and Henry Kissinger ended two decades of unremitting Sino-American hostility since the advent of the People's Republic and the withdrawal of Chiang Kai-shek's Kuomintang government to Taiwan.
Washington was Taiwan's chief backer during these decades of estrangement with Peking, and the treatment of Taiwan thus became the major stumbling block in the way of unfreezing Washington-Peking relations. Somehow the two capitals managed to finesse the issue, and on Jan. 1, 1979, the US normalized diplomatic relations with Peking while keeping up informal ties with ''the people of Taiwan.''
Then came the election campaign of 1980, when Ronald Reagan's repeated calls for more ''official'' ties with Taiwan reawakened all Peking's suspicions regarding Washington's ultimate purposes.
Thus the Reagan administration got off to an inauspicious start in relations with China. Even after the communique of Aug. 17, 1982, agreeing to limit American arms sales to Taiwan, irritations on other issues have kept relations cool.
It was only this summer, after Commerce Secretary Malcolm Baldrige's visit to Peking at the end of May, that some sense of forward momentum has been restored to Sino-American relations.
Mr. Baldrige brought Peking word that after months of intense internal debate , Washington was finally ready to treat China as a ''friendly country'' regarding the transfer of sophisticated dual-use technology - technology with both military and civilian applications. Then followed a textile agreement after months of tense negotiations, and the possibility of a nuclear agreement that will permit the transfer of civilian nuclear technology from the US to China.
Now comes Mr. Weinberger's visit to China, significant because, within the Washington bureaucracy, the Pentagon was the most strenuous opponent of the transfer of dual-use technology to China, even though it sees the strategic value of China in Washington's global confrontation with Moscow.
It remains to be seen whether the Weinberger visit will resolve the contradiction between the desire to enlist China as a partner to help restrain Soviet expansionism, and wariness of China as being, after all a communist country. The contradiction is felt at many levels of the administration from President Reagan down to the humblest participant in policy planning. If the fear of Soviet expansionism is removed, what common interests do China and the US share?
So far, neither Peking nor Washington has come forward with convincing, clearcut answers to this question. This accounts for much of the uncertainty surrounding relations between the two capitals. To what extent can or should Washington and Peking coordinate their strategies toward the Soviet Union? Can the two find common ground over a much wider range of issues, both economic and political? There is evidence that both sides are trying - one of the most telling being the presence in the US of 8,000 to 10,000 Chinese students, at least half of whom are there on government grants mostly in the scientific and technological fields.
To expect a total convergence of strategic views between Peking and Washington is probably unrealistic. The Taiwan issue will not go away. Mr. Reagan says he will not abandon old friends just to make new friends, while Peking has not changed its insistence that anything smacking of officiality in the American-Taiwan relationship - even the granting of visas or the authorization of commercial flights - infringes on China's sovereignty.
There are also less important but continuing differences over the Middle East (where Peking upholds the Palestinian cause) and over Africa (where Peking is impatient with Western willingness to compromise with South Africa over independence for Southwest Africa).
At the same time, Washington and Peking share similar views on the importance of getting Soviet troops out of Afghanistan and Vietnamese troops out of Kampuchea. The Weinberger visit could well lead to a reaffirmation of parallel strategic interests such as characterized former Defense Secretary Harold Brown's visit to Peking in January 1980.
Peking has embarked on a process of normalizing its relations with Moscow. This process will continue whatever happens in Sino-American relations. But as Chinese officials frequently point out, a more peaceful Sino-Soviet border, increased trade, and some resumption of cultural and sports exchanges do not by any means foreshadow a return to the ''lean-to-one-side'' closeness of the early 1950s when China and Moscow were allies.
In the end, the real question for the US, and for the West, is not whether China will be friend or foe in confrontation with the Soviet Union, but whether China's modernization drive will succeed. The inner logic driving the Chinese leadership in all its external relations today is the priority of the economic modernization campaign. Without modernization China cannot hope to reunite with Taiwan peacefully, nor will it gain the weight in world councils to which it aspires.
And China's leaders - Deng himself, Premier Zhao Ziyang, and General Secretary Hu Yaobang - have decided that modernization will be achieved by seeking cooperation with the West - the US, Western Europe, and Japan.
They are communists, but the economic and political structures they have worked out are flexible and evolutionary. They have held down the military budget. Their approach to the Soviet Union for normalization is within this context - they need a peaceful international environment in which to achieve their goals.
They are now engaged in negotiations with Britain over the future of Hong Kong that will test their flexibility to its utmost. Can they regain sovereignty over Hong Kong yet keep it an island of capitalistic prosperity?
Thus, the goals of China's leaders are domestic, yet the process of working toward these goals touches on every facet of China's external relations and most particularly on its relations with the West. As the principal Western power, the US cannot but be vitally interested in the outcome of this effort.
Besides the US, no country has a greater interest in and concern about China's future than Japan, China's closest island neighbor. Japan's population is one-tenth that of China, its land area one twenty-fifth. A powerful, friendly China complements the security Japan gains from its alliance with the US. A powerful, hostile China immeasurably complicates Japan's security task, faced as the nation already is by the seemingly inexorable increase in the hostile, offensive capability of the Soviet superpower.
During the 1950s and '60s, Japan reluctantly went along with the policy of containment - both of the Soviet Union and of China. Tokyo, however, early established informal relations with Peking even while maintaining formal diplomatic ties with Taiwan. No country welcomed Sino-American detente more than Japan. Disappointment over not being told in advance of the Nixon-Kissinger opening to Peking in 1971 soon gave way to profound relief that Washington and Peking were no longer enemies.