Forty-two years after the unconditional surrender of the Japanese empire, some U.S. officials are feverishly warning of a new outbreak of hostilities between the United States and Japan: an all-out economic war, touched off by Japanese trade surpluses and congressional retaliation.

Don't believe it. For all the steamy rhetoric filling the air over Washington, cooler heads will prevail. Even the hotheads in Congress can be presumed to have enough sense not to go for tough-seeming, shortsighted trade restrictions that would prove disastrous over the long run.

The greatest roadblock to protectionist folly, of course, is the White House. President Reagan will stand firm on his commitment to free trade, resisting any more restrictive ac-tions that will discourage Japanese imports.

The reason for Reagan's stubbornness, of course, is that he realizes the importance to the U.S. economy of Japanese imports, and the harm that would be done if they were significantly reduced. And one reason he is aware of this is the subtle but pervasive influence of the Japanese lobby in both business and government circles.

The Japanese lobby, working quietly and effectively, has now be-come one of the most influentialin Washington. The pressure Tokyo can bring to bear through its myriad U.S. importers and retailers is enormous.

And there are other factors that will help to ease the situation. The revaluation of the yen will cut into Japan's huge trade surpluses, as will the growing Japanese investment in foreign industry. Another hopeful sign is the resurgence of U.S. manufacturers in the competition for world markets.

The pessimists point to Japanese industrial and financial corporations' increasing diversification, and their tendency to be less subservient to their government's ''administrative guidance'' -- meaning production controls. But our sources in Tokyo say this does not portend irresponsibility by Japanese business. At the first signs of a trade war with the United States, Japanese corporations and the Tokyo government would quickly come up with ''voluntary'' restrictions to appease the economic hawks in Congress.

Actually, Japan's success in world trade has given it enough to wor-ry about. The last thing the Japa-nese need is a major trade war with the United States and all it would entail.

Japan's big problem is its liquidity glut; it has more money coming in than it can handle. Bloated by trade surpluses, massive personal savings, stagnation in domestic consumption and the yen's growing value in relation to the dollar, Japan has so much money to get rid of that it is making bad investment decisions both at home and abroad.

Some administration officials have been following with alarm the fluctuations of the booming Tokyo stock market. With cash burning holes in their pockets, Japanese investors are paying too little attention to the fundamentals, like company earnings.

In fact, a perceptive but little-noticed study by the First National Bank of Chicago concluded that if a world depression comes anytime soon, it will be touched off by a stock market crash in Tokyo. The reasoning is that, just as the 1930s depression was triggered by the 1929 crash of the New York stock market because the United States had replaced Britain as supplier of capital to the world, today Japan is supplanting the United States in that role.

In short, no one in authority, either in Washington or in Tokyo, is likely to risk a U.S.-Japanese trade war that could rock the Tokyo market and lead to an eventual global depression of hair-curling proportions.