THE INFLATION RATE is coming down, but not nearly so fast as the consumer price index suggests. The effervescent CPI always speaks the truth, but not necessarily the whole truth. It is heavily influenced by several categories such as fuel prices that bounce wildly around, and it rose only three-tenths of 1 percent last month. As the White House promptly and loudly pointed out, that's a good sign.

But it is a little too good. At risk of spoiling the celebration, we have to point out that the true inflation rate currently is not around 4 percent a year, as the CPI indicates. It is somewhere between 8 and 9 percent. That's not very different from the rate last summer. To find the rate so stubborn in the face of a recession that started in July is not such a good sign.

One way to estimate the underlying inflation rate is to follow labor costs. It is the pattern of wage increases that keeps the inflationary cycle going, from higher prices to higher wages back to higher prices. The Bureau of Labor Statistics has just published its employment cost index for the last quarter of 1981, and that number deserves attention. It is particularly valuable because it covers not only wages and salaries, but fringe benefits as well--and the fringes have consistently been rising faster than cash wages. From October through December, total compensation in the private non-farm economy rose at a rate of a little more than 8 percent a year--not much different from a year earlier. It's quite true that by the end of 1981 there were a lot more people unemployed than a year earlier. But for those who were still working, wages and benefits were still rising rapidly and, in turn, inciting future price increases.

To the limited extent to which inflation has slowed, it is due chiefly to the recession. The White House vigorously resists that thought. It claims credit for lower inflation, but says that it had nothing to do with the recession. Unfortunately, the two go together.

In the deep recession of 1975, the CPI behaved much as it is behaving now. The country generally assumed that the long inflation was finally defeated. Under stimulative policy, the economy began to grow again at a fairly rapid rate--and, within a couple of years, the inflation again broke into a brisk trot upward. This year, a recovery would begin with wages and benefits alreadly rising quite rapidly. With economic growth and employment beginning to pick up, it would be extremely difficult to keep labor costs from generating a new surge in the CPI.

Several months of relatively good behavior by the CPI this winter could generate a strong temptation, in the administration and Congress, to declare a victory over inflation and leap to the more congenial job of pumping up an economic recovery. That's why it remains imperative to remember past experience, and keep the underlying rates of inflation clearly in mind.