IS IT TIME to stop worrying about inflation? The consumer price index has been behaving relatively well lately. The most recent number, published this week, suggests an inflation rate of about 5 percent over the past year. There's a strong temptation to declare a victory over inflation and turn attention to employment.

Before you join that parade, you might want to reflect briefly that there is more than one way to measure inflation--and the present consumer price index is not the best of them. It is excitable and, like all the excitable people you know, it has a tendency to exaggerate. Most of the trouble arises from the peculiar way in which it handles mortgage interest rates. Over the past several years, when mortgage rates were rising, the CPI overstated inflation. Now that mortgage rates are falling, the CPI understates inflation.

The CPI's authors at the Bureau of Labor Statistics are well aware of this peculiarity, and for some time they have been publishing, as an experiment, an alternative price index that eliminates mortgage interest. Instead, to provide a better measure of the true cost of housing, it uses figures for the rent of equivalent accommodations. Beginning next January, the government is going to replace the present slightly defective CPI with this new formula. If it had been in effect in 1980, instead of a consumer price increase of 12.4 percent, it would have shown an increase of 10.8 percent. But instead of 5.1 percent over the past 12 months, it would have shown an increase of 5.6 percent -- still quite a drop, but not so spectacular a drop as President Reagan has claimed.

And then there's the underlying trend of inflation. By any measure, the CPI is currently below that trend -- partly because of good harvests and falling prices of foodstuffs, partly because of the high foreign exchange rate of the dollar. The best measure of the trend is labor costs. They are rising faster than the familiar statistics on wages might suggest, because those statistics count only cash wages, and fringe benefits are increasing much more rapidly. Including the fringes, labor compensation rose more than 7 percent in the year ending last September.

What should you conclude from all this tedious arithmetic? First, inflation has fallen significantly since Mr. Reagan took office. Second, it has not fallen quite so significantly as he thinks. It is down from 10-plus a year to about 7 percent. It is certainly time for public policy to start giving more attention to unemployment. But that has to be done cautiously, for inflation, by any accurate standard, is still too high for safety.