THE INFLATION rate for consumers is now running about 4.5 percent a year. Everyone agrees that it's a moderate rate, at least by recent standards. But it's up just a little from last year. Perhaps the question to ask is why inflation is as high as it is, at a time when the costs of raw materials and fuel have been falling.

The consumer price index gives a pretty clear answer. Inflation in housing costs picked up again sharply over the summer. Prices of houses, rents and insurance are all up substantially. Utility rates are up even more.

Housing is by far the most important component of the CPI, but other things are going up as well. Inflation in medical care continues, like inflation in most other personal services. College tuition is another notorious example.

The present pattern is the reverse of the familiar one of the 1970s. In those years the great surges of inflation began with commodities traded on world markets -- most spectacularly oil, but at one time or another grain, metals and a great variety of other industrial raw materials as well. Now those markets are going the other way. It's not only the price of oil that's falling. The price indices for the whole range of foodstuffs, industrial supplies and, at the wholesale level, finished goods have been generally declining since early summer. But that doesn't much affect housing costs, and, in many of the service industries, the insidious habit of regular price increases is continuing. If inflation in this country is trotting along at 4.5 percent a year at a time when prices of basic commodities are falling, there is reason for at least a shadow of concern about the speed at which it might run when commodity prices stabilize.

That's another reason to keep your eye on the most important price of all, the price of the U.S. dollar on the exchange markets. Prices of many commodities -- in dollars -- have been falling because the dollar's exchange rate has been rising. A drop of $2 a barrel in the price of oil will still leave that barrel more expensive, in most other currencies, than it was last spring. The dollar is unlikely to remain at its present very high level for long. When and if it comes down, the present mechanism will go into reverse. As imports get more expensive, a new wave of inflationary pressures inevitably will seize the country.

It's entirely proper for Americans to congratulate themselves on an inflation rate that is now far lower than it was several years ago. But it would be more useful to start thinking about ways to meet and contain the next cycle of inflation that will arrive when the dollar starts to drop.