ONCE AGAIN the American trade deficit has soared, this time to a new record, and once again people shake their heads and say that it was totally unexpected. But aren't those deficits part of a well-established pattern of national self-indulgence? The country likes buying more than it produces and doesn't see why it shouldn't continue. President Reagan doesn't see why it shouldn't, either, and the opposition in Congress isn't anxious to press him.

These latest figures are for October, and it's true that October trade deficits have regularly been the highest of the year. It's also true that the dollar value of imports is up because the exchange rate of the dollar is rapidly falling. But the October report is full of indications of deeper changes. The United States is now running deficits in important categories of manufactured goods that have been American specialties -- computers, chemicals and heavy industrial machinery. Oil imports are up sharply and expensively over last year.

The administration seems to be counting on the falling dollar to balance the country's trade, eventually, without any need for unpleasant and unpopular public decisions on its part. According to this hopeful assumption, the higher prices of imports will discourage people from buying them, while the cheapness of American exports abroad will make them highly competitive and create new jobs in the export industries. Unfortunately, those are precepts from a textbook that is now slightly obsolete.

The rising prices of imports -- and they are now beginning to rise substantially -- will doubtless persuade people not to buy. But they will also introduce a new round of inflation. As for the export boom, a falling currency alone won't create it. There's plenty of experience abroad to demonstrate that. Britain has repeatedly turned to devaluation to get its trade in balance. Why is it that manufacturing employment has fallen faster in Britain over the past two decades than in any other major industrial country -- and West Germany, with a currency that has risen over the same decades, has now emerged as the world's strongest exporter?

To get American trade into balance without severe and lasting damage to the economy will take two things: lower consumption and higher investment. The first step is to get the federal budget deficit down. The president and Congress have taken a pass on that one. Their current agreement on the budget deficit will only hold it at its present level. But if the government won't take action, the markets will do the job -- and you have seen that begin to happen this autumn.