IS THE ECONOMY now heading upward or downward? You can find plenty of evidence for either view. Economics is misbehaving again.

At the beginning of the month, it looked as though the Federal Reserve Board had choked off the money supply too tightly, with high interest rates rapidly pushing the economy into a damaging recession. The leading indicators had been falling for two months, and the president's chief economic adviser, Murray Weidenbaum, spoke of a "pronounced slowing" of business activity. Automobile sales were sinking. The extremely high exchange rates of the dollar were helping to reduce inflation, but foreshadowed serious trouble for American exports.

Then came the unemployment figures for July, showing -- to everybody's stunned surprise -- a substantial drop. Unemployment had fallen to the lowest rate in more than a year. Next came the figures on industrial production and, despite the troubles of the automobile companies, production was up. Now it appears that, although intest rates were steadily rising from June into July, housing starts were also rising.

That leaves the economists in an interesting position. For every statistical indicator pointing in one direction, they have another, equally valid, pointing in the other. It's an unusually clear illustration of the way the old relationships -- the formulas that people once thought to be rigid and inherent in the economy -- have gone spongy, perverse and unreliable. rThe reasons for it, as you hardly need to be told, go back to inflation and the radical differences it makes in the ways people think about money. Most people seem to have assumed, during the first great surge in the early 1970s, that inflaction was a passing phenomenon. But when it began to accelerate again around 1978, people began changing their money habits in ways that promise to be permanent -- and that make forecasting more difficult than ever.

It means that the early warming system for anticipating economic trouble has become progressively less trustworthy. In the Carter years, the government repeatedly aggravated inflation by reacting too promptly to signals -- usually flase -- of impending recession. This time, the people who make public policy have little choice, amidst this confusion of numbers, but to sit tight, change nothing, and wait to see what happens next.