ANOTHER LURCH downward for both the stock market and the dollar. While the stock market gets more attention, it is being driven now by the dollar's declining exchange rate and the resulting prospect of higher inflation and higher interest rates. There's been a change here: the dollar fell for 2 1/2 years, until this autumn, without affecting the stock market. Why now? The answer seems to be that people in the financial markets thought, until several months ago, that the dollar's descent was being carefully controlled by the governments of the wealthy industrial countries. Currently, in contrast, the impression has got around that it's out of control and nobody's in charge. That impression is, unfortunately, correct.

There is much anxious talk of a meeting of the seven big industrial democracies to try to regain control of the exchange rates, but the outlook isn't very promising. Since the United States is running an international deficit of more than $150 billion a year, stabilizing the dollar means that somebody has to come up with a way to finance it. The dollar will hold at a constant exchange rate only if capital is flowing into this country fast enough to balance that deficit.

The money can come either from foreign governments or from private investors in other countries. Until this year it was coming from private investors, but last winter they turned away from the dollar. Since then, support has come almost entirely from foreign governments. But not even Japan and West Germany are prepared to put $150 billion a year of their money into American dollars indefinitely. It's possible to bring more private money back into the market, but that would take higher interest rates -- and would probably mean a recession in an election year.

No one in American politics, in either party, seems eager to lead the voters into the process known, when it is imposed on smaller countries, as adjustment. That signifies mandatory deficit-cutting as the condition for international help. Americans are currently talking as though the choice were between the exchange rate and the domestic economy, one of which could be sacrificed to save the other.

More accurately, the choice is between deficit-cutting now and deficit-cutting later. By their joint performance over the past month, both the administration and the congressional Democrats have signaled a strong inclination for procrastination, and the budget deficit is directly related to the American trade deficit. With that, the financial markets keep falling. It's dismaying, but it's not irrational, and there's no great mystery why it's happening