THE TROUBLE starts with the imbalance. Japan sells the United States a great deal more than it buys from the United States. The difference will run to $8 billion this year. Sales mean jobs, and the point is exceedingly sensitive in both countries. That's why American trade negotiators have been hammering on Japan to cut its trade surplus, and that's also why the Japanese have been reluctant to commit themselves.

The United States has begun to get loud and peremptory with its complaints. That's not ordinarily the ideal way to conduct trade negotiations. But there is a widespread impression in Washington that the huge Japanese surplus arises from deeply ingrained Japanese ways of doing things, and these habits do not respond to the usual murmurs of diplomacy. In mid-November an American official arrived in Tokyo with a list of requests and very shortly began letting it be known, quite publicly, that the Japanese were not, in his view, taking them sufficiently seriously. A few days later, after further talks, he returned home accompanied by a shower of Japanese denunciations for his arrogance and bad manners.

But then an interesting thing happened. This week Prime Minister Takeo Fukuda reorganized his Cabinet in a manner that looks, from the Carter administration's perspective, rather hopeful. For one thing he has given broad authority to Nobuhiko Ushiba, a former Japanese ambassador to this country, who is known here as a wise and skillful econimist. Mr. Ushiba will apparently have the power to break the impasse that has prevailed until now within the Japanese government.

If the Japanese government is preparing to move, the next question is where it will decide to go. Is the United States asking for the right things? If it is asking the Japanese for a firm date by which its trade surplus will hit zero - when their imports will equal their exports - then it is mistaken. No country can control its trade accounts precisely.

But the Carter administration's basic thrust is clearly right. In the Nixon years, this country made sporadic efforts to deal with some of the imports from Japan by trying to keep them out. The Carter administration, instead, is pressing the Japanese to increase their own imports from this country and everywhere else. To do it, Japan will have to stimulate business activity at home and reduce its barriers to foreign goods.

What if it doesn't? American negotiators have done a lot of talking about the possibility of an unmanageable surge of protectionism in Congress. But there is a much more immediate, and automatic, sanction. The exchange rate of the yen has risen rapidly in recent months on the international money markets. That makes Japanese goods more expensive abroad - and harder to sell. A massive surplus tends to be, in time, self-correcting. But, unfortunately, that mechanism works slowly and does a lot of damage along the way to the export industries, which are usually a country's most efficient producers.

Among the world's great trading nations, Japan is now second only to the United States in economic power.Perhaps because of its extremely rapid rise in wealth, Japan has yet to come to terms with the effect of its trade policies on other countries. Without really intending it, the Japanese now find themselves with a tremendous trade surplus that is a burden to the world in general and to their best customers on particular. It is important for Americans to recognize that this surplus cannot be pushed down overnight. But it is equally important for the Japanese to recognize that a surplus on the present scale cannot be sustained much longer.