Yasuhiro Nakasone is the 12th conservative politician to become Japan's prime minister since the end of the postwar occupation. Next week, he will make the visit, customary for a new prime minister, to a Washington where hostility toward Japan is greater than at any time since 1945.

At least that is the impression one gets from the statements of many of our politicians and officials. Several years ago, in another period of aggravated relations, a leading member of the government referred to Japan as "that monster we have created." Similar but less affectionate expressions can be heard today. Rumor is that the president has been advised to greet Nakasone with a new sanction on Japanese imports.

Postwar Japan is an extraordinary success story. Reflective Japanese may comfort themselves with the thought that success can evoke sentiments beyond admiration, resentment being one. Americans might consider that Japan is our success story too.

After a war fought with great bitterness, America turned from thoughts of a vengeful peace to recreating Japan as a pacific democracy. Douglas MacArthur's occupation can be given too much credit, but the fact is that the political institutions and the reforms dating from the general's reign have flourished amazingly.

Japan today is one of those few nations in which popular elections, civil rights, a free press and independent courts are taken for granted. From a society where a half-century ago political assassination was acceptable, Japan has become a model of political and social stability and of widely shared well-being.

This is not to idealize matters. There is much to criticize about Japan, particularly its policies toward the outer world. Still, perspective is useful, and so is common sense.

Not for the first time, we are unhappy about Japanese defense expenditures. Japan's constitution, written, it is said, in Gen. Douglas MacArthur's headquarters, abjures not only war but even the creation of "land, sea, and air forces." These sweeping strictures have not prevented Japan from building the world's eighth-ranking military force. But the constitution is a restraint, and so is the absence of a strong constituency for defense spending. By our standards the defense budget is exceedingly modest.

Of course, Japan could do more for its own defense. The critical shortcomings of the Self-Defense Forces are not in ships and planes but in supplies of ammunition, missiles, fuel and so on. Remedying these would strengthen allied capabilities in Northeast Asia, either further deterring the Soviets or causing Moscow to spend more in the Far East.

What we should not expect is budgetary savings. The two Marine regiments in Okinawa might go to Hawaii, but their pay and allowances would go along. The Seventh Fleet could count on more support from the Japanese, but its ships would not be retired, nor would the Navy leave the base at Yokosuka, for which the nearest alternative is Pearl Harbor. (Japan, incidentally, contributes a billion dollars yearly to help maintain the American bases.)

The hope that more defense spending would be the means to weaken Japan competitively is as illusory as it is mean-spirited. The Japanese economy is operating below potential and easily could meet additional military demands.

Eminences in the Democratic Party and in the administration tell us that Japan is unfair. Our market is open, Japan's is closed. Moreover, through something called industrial policy, Japan threatens to catch up or surpass us in high technology, endangering our national security.

These are complex matters. It is true that Japan still has a number of egregious restrictions on imports. So have we, but Japan has the trade surplus. Victimized most are Japanese consumers, but the irritation of exporters is justifiable.

Nakasone is reported to be coming with concessions, including, unhappily for consumers, continued restraints on automobile exports. He has been in office seven weeks, not long enough to have negotiated with his colleagues the toughest ones, the quotas on beef and citrus. Eventually, he will have to risk shortening his tenure in order to reduce trade tensions in U.S.-Japan relations.

It is well to remember that we are concerned with specific irritants, some involving quite small amounts of trade. Their removal, desirable as that will be, cannot much change the U.S.-Japan trade imbalance, which has its roots in economic structures.

Our semi-panic about Japanese advances in high technology is a curiosity. Is it that our market-oriented society fears competition? Is it that the Japanese government subsidizes industrial R & D? It does, but on a smaller scale than anywhere else. Does the government promote research cooperation among private firms? Yes, but this is an option open to anyone. And the results in Japan have been in no way spectacular.

Much that is written about Japan's industrial policy successes is grossly inflated. This is partly because the observers accept Japanese bureaucratic puffery. Some is based on statistics out of control. For example, Japanese high-performance semiconductors have not taken 70 percent of the American market-- at least not if the in-house production of IBM and AT&T is counted. Recent news stories state as fact that Japanese machine tool makers receive an annual billion-dollar subsidy, a figure wildly distant from reality.

The Republican 1980 platform said that Japan would be "the pillar of American policy in Asia." Some of the current rhetoric, from both Democrats and Republicans, seems to say that Japan is enemy No. 1. This cannot be seriously meant. Japan's government and citizens do not conduct themselves always or altogether as we would wish. But it is preposterous to view Japan, especially a prospering Japan, as inimical to our interests. Nakasone's visit may be an occasion for President Reagan to say as much.