By STEPHEN MOORE

The class warfare lobby is singing its “soak the rich” anthem again.

A just-released report by the liberal Center on Budget and Policy Priorities suggests that “income disparities between the top fifth of families with children and families at the bottom and middle of the income scale have grown substantially over the last two decades.”

The report comes just one month after the latest release by the Census Bureau on income and poverty levels. Income redistributionists seized upon the census data to declare that, in America, the rich are getting richer and the poor are getting poorer.

Is the divide really growing as rapidly as those reports indicate?

Admittedly, there is some bad news. The poorest 20 percent of Americans saw their incomes decline in real terms by 2 percent last year, while the richest fifth saw their real incomes rise by 2 percent. Today, the top 20 percent have about half of the total income in America up from about 46 percent in 1990.

But there are several encouraging trends in Americans’ income since 1980.

First, Americans are constantly moving up and down the income ladder. This phenomenon is known as income mobility and it is almost unique to the American experience. Yes, there are millions of poor households today. But they are not the same families that were poor 10 or 20 years ago.

The statistic that best captures this point comes from the Census Bureau, which found that a family that was “poor” in 1980 (i.e., the poorest 20 percent in income) was more likely to have moved all the way up to the richest fifth in income than to have remained poor at the end of the decade.

Second, family incomes, adjusted for size of household, show a fairly steady ascent over the past 25 years. Here are the numbers for a family of four in 1996 dollars:

– 1970 $42,458

– 1980 $46,536

– 1996 $51,405

The median family income data do not show nearly the same amount of improvement. Why? Because the average household is smaller today than 20 years ago. A family of four with a $60,000 income that ends up in divorce now has two incomes of $30,000, which leads to a 50 percent decline in household income even though the total income has not declined by even a penny.

Third, the great American middle class is not stumbling down the income ladder, as the CBPP study implies. Here is the statistic that troubles the left: in 1970, about 62 percent of American households had incomes between $15,000 and $50,000 today only about half do. The middle class appears to be disappearing.

But here’s why: In 1970, only 22 percent of households had incomes of more than $50,000 a year (in 1992 dollars). Today, 35 percent do. In other words, fewer families fall in the “middle-class” category today because many have experienced such big gains in income that they are now classified as rich. This is hardly a trend we should fret about.

Fourth, Americans are more asset-rich than ever before. In the past 15 years the United States has seen the greatest increase in wealth in human history. The value of land, capital and businesses has increased by a minimum of $8 trillion since 1980.

Has all that wealth been hoarded by the already-rich? Not by a long shot. Read the fabulous bestseller “The Millionaire Next Door.” It is filled with tales of Americans who never made over $50,000 a year in their lives but, through a combination of thrift and shrewd investing, are now asset-millionaires who are financially self-reliant.

Finally, wages, when properly measured, are not falling. They are higher than ever before. The National Center for Policy Analysis shows that because of the increasing value of fringe benefits such as health care coverage, pensions and more leave and vacation time median hourly worker compensation has doubled since the mid-1950s and is up by about 20 percent since 1980.

All of this is not to say that all Americans are doing better in this new information-age economy. Social critics are right: there have been painful displacement costs to millions of Americans as industries have sucked in their bellies to become more cost-competitive.

But before we come up with policy solutions, we all have to understand what the data are telling us.

It’s a natural human tendency to think of the past as “the good ol’ days.” But in terms of incomes, for the vast majority of Americans, these are the good old days. The rising tide of the last 15 years may not have lifted every boat, but it has lifted most.

Stephen Moore is director of fiscal policy studies at the Cato Institute.