Japan steps up defense -- but only under US pressure

''In terms of economic power, we have reached the stage where we can be an equal partner of the United States,'' the defense official said.

''In terms of military power, we are still a third- or fourth-class country.''

Prime Minister Zenko Suzuki frequently tells his people that they must have the will ''to defend our own country ourselves'' and that defense expenditures must be progressively increased in line with this determination. But the major driving force for substantially greater defense spending comes from outside the country, the United States, rather than from within.

Hence the prime minister faces a tough fight in the parliament session opening at the end of this month over his approval of a $11.8 billion defense budget for the coming fiscal year (April 1982 through March 1983), some 7.75 percent more than last year's budget.

The government's budget as a whole is the most austere since 1956, in that general account spending increases have been held to 6.2 percent and vote-winning expenditures on welfare and education have had only token increases of 2.3 and 1.8 percent, respectively. The increase in the public works budget is zero.

Thus what the Japanese call the ''protrusion'' of the defense budget in the total government budget for the coming year is conspicuous in the extreme. Even moderate opposition parties such as the Democratic Socialists, who favor greater defense expenditures by Japan, have said that there should have been a better balance between increases in defense spending and spending for domestic programs like welfare.

Yet defense officials here concede that, quite aside from relying on the US nuclear umbrella, Japan will be heavily dependent on US conventional defenses in time of need.

If, for instance, there were to be a Soviet attack on the northern island of Hokkaido, Japan's air and maritime Self-Defense Forces would probably coordinate their actions with American naval and air units almost from the moment of attack. Ground units on Hokkaido could hold out for a month -- ''at least that is what we hope'' said one official -- but they, too, want American reinforcements, and the earlier, the better.

Japan's Self-Defense Forces are severely constrained by the postwar Constitution, which forbids ''war potential,'' and by the Self-Defense Forces law, which does not, for instance, allow the Self-Defense Force to be used in United Nations peacekeeping operations.

While, over the years, the Japanese public (86 percent of it, according to a recent poll) has come to accept the need for Japan to have defense forces, there is little support for a substantial increase in the Self-Defense Force's capabilities.

The public seems quite content to keep defense spending at or below 1 percent of gross national product (the 1982 budget will raise great concern that politicians and bureaucrats have over trade frictions with the US.

With Japan's exports to the US exceeding imports by $18 billion and with American unemployment, inflation, and interest rates all much higher than those of Japan, leaders here fear a rapid growth of protectionist sentiment in the US.

They know Americans also feel that Japan is doing too little in the security field. Their often unspoken reaction is, ''Since there seems to be no easy or rapid method to reduce the trade imbalance dramatically, at least let us do what we can in the field of defense.''

This feeling has become a common denominator bringing together finance and trade ministry bureaucrats with businessmen and politicians concerned with Japanese-American relations or in the defense lobby. It is not a healthy development, many defense experts concede, in the sense that it does not result from a clear vision as to what Japan's own self-defense goals should be, nor how these are to be achieved.

Nevertheless the Suzuki Cabinet's decision on the 1982 defense budget has averted one potentially serious area of Japanese-American disagreement and smoothed the way for the security consultative conference between top US and Japanese defense and diplomatic officials that is to be held here Jan. 8.

This conference, involving Japan's foreign and defense ministers, the commander in chief of the US Pacific Fleet, and the US ambassador to Japan, will continue and refine the joint planning for emergencies that was begun under guidelines set up three years ago. On the agenda will be scenarios for responses to direct attacks on Japan.

This kind of joint defense planning has become more detailed and specific during the past three years. Joint maneuvers have also become more frequent.

In Ambassador Mike Mansfield's words, the US hopes Japan will consider filling some of the ''voids and vacancies'' caused by the shift of American resources to the Indian Ocean -- not that Washington thinks Japan should become a regional or a world military power, but rather ''because we think that the primary responsibility for the defense of Japan lies with Japan.''