Japan has long been reluctant to devote a larger portion of its massive and vigorous economy to defense. Hence it is noteworthy that the government has decided to boost the military budget for fiscal 1982 by almost 7.8 percent, or 4 .5 percent in real terms. This is a creditable effort considering the fact that Japan, not unlike other highly industrialized countries, wrestles with budget austerities and also the fact that the Japanese people would far prefer spending more money on social welfare and education.
The decision was made, of course, in response to United States pressure. Strains have developed in Japanese-US relations because Washington has long felt that Japan should contribute more in the defense field. The present US administration is even urging Japan to take over defense of sea lanes in the Far East - a call dictated by the growing Soviet military presence in Asia and increased US military responsiblities around the globe.
Japan has not gone as far as the US would like. Military outlays will still be under 1 percent of the gross national product (as compared with 6 percent for the US) and account for only 5 percent of the total budget. This is not enough. Yet it is, as the Pentagon comments, ''a sound beginning'' which sets the pattern for continuing increases.
We know it is not easy for the Japanese to move in this direction given their antimilitary attitudes and a postwar Constitution banning ''war potential'' and the right of belligerency. In fairness, too, account should be taken of the substantial contribution which Japan makes to world stability in the form of economic aid to third-world countries.
However, without impinging on its legal ban on anything but ''self-defense forces,'' Japan is in a position to do more than it has. Defense of the noncommunist world is a collective undertaking. NATO members, too, are being asked to hike military expenditures at a time of financial strain. Though Japan has won wide admiration for its economic achievements, its image suffers somewhat from the perception that these were possible in part thanks to the small proportion of resources being devoted to defense and to the protection of the US nuclear umbrella.
Surely Japan wants to rise to full acceptance of the responsibilities demanded of a great economic power. It would be nice to think that future steps in this direction will come not from the prodding of a close ally but out of the Japanese people's own awareness of their opportunities to be helpful in the world and an eagerness to fulfill them.