Suddenly, congressional Democrats have fastened on to "the fairness issue."

With a large army in Saudi Arabia, with support for the expedition from Germany and Japan eroding, with the American economy tottering on the brink of what could become a serious recession, Congress has become locked in a bitter bipartisan battle over whom to tax. After all, the election is just a month away.

So the analysis du jour is that class warfare is making a comeback.

Is it really?

Down beneath the partisan broadsides, what's been happening to the distribution of income in America these last 10 years? It would help to know what the numbers say.

Following economist Herbert Stein, it makes sense to start at the bottom. There is one group, he says, perhaps 1 percent of the population, that constitutes an underclass. They live with little hope in urban squalor amid crime and drug addiction, drop out of school easily and have high rates of illegitimacy.

There is another group, perhaps 10 percent of the population, says Stein, that is "poor by American standards." This fraction, after declining until about 10 or 15 years ago, has been static since.

Then there is the great middle class, some 75 percent or 80 percent of the population, that does all right, except that their income hasn't been growing much in the 1980s. Their wages and their pensions cover the cost of living in a certain way they think of as being vaguely middle class; they have houses, cars, televisions, food, vacations. They are worried about being able to maintain their standard of living in the future and about the quality of their schools and their medical care.

Above them are those who comprise the upper middle class, another 5 percent or so, most of whom live in families that make more than $75,000 a year. With approximately 65 million families in the country, this adds up to about 3.5 million families; they live in the best suburbs, drive the BMWs and so forth.

Finally, there are the truly rich, another 1 percent or so of the population, those who make $200,000 or more, who control vast amounts of wealth. Even more than the upper middle class, the value of their holdings soared during the 1980s.

Now, ordinarily, the large middle-income group doesn't get decomposed very much. They are assumed to think and act pretty much as one big group, beguiled by President Reagan one year, worried about the Japanese the next, content to be "in between." But the big noise in this field for a couple of years has been the research of technical economists Larry Katz of Harvard University and Kevin Murphy of the University of Chicago. And what they have found is that the middle class is indeed in some danger of coming apart.

What Katz and Murphy found is that a serious gap has opened up between white-collar workers and older blue-collar workers on the one hand, and new kids who went to work in the 1980s without a college degree on the other. The college wage premium rose from 1963 to 1971, fell from 1971 to 1979, then rose sharply from 1979 to 1987, they report. Meanwhile, the experience differential was widening, too.

The inescapable conclusion is that new blue-collar workers are not going to do as well as did their parents' generation.

Why? What turned around so abruptly the palmy atmosphere of the 1970s, when auto workers vacationed in France, and plumbers and bakers liked to joke that they made as much as doctors (though they didn't)? It's a complicated story, naturally. But the Katz and Murphy findings boil down to two main themes, both of them familiar to readers of the business pages.

One has to do with the increasing demand for kids with college degrees and well-developed skills in high-technology and service industries. The other has to do with sharply declining demand for unskilled workers in traditional manufacturing industries.

Why did this happen? There's no particular mystery to it, says Frank Levy of the University of Maryland, another specialist in the study of the distribution of income. He says the long borrowing spree of the Reagan administration made it difficult for manufacturers to compete on the world stage or even at home, first raising dramatically the value of the dollar, then keeping real interest rates high. Employers laid off workers, busted unions and bought automating machinery as fast as they could.

The result was to depress blue-collar wages. Certain kinds of families -- the young, those with key workers unemployed, those headed by the poorly-educated -- were, for a time at least, "left behind," in economist Katherine Bradbury's phrase.

"If the trade deficit had clobbered the income of newscasters, it would have been a different story," says Levy. "When it first happened {the dollar's rise}, there was all this Wall Street Journal euphoria. They said, 'My God, that just shows what a great country this is, everybody wants to be here.' The first guy to say 'wait a second' was {Commerce Secretary} Malcolm Baldrige, who was getting reports from the field that said, 'My people are getting destroyed by this.' "

In due course, the dollar came down, and many American manufacturing firms adjusted to new competitive realities. But big government deficits are keeping the cost of capital in America high; the national savings rate has reached a dismal level. And so Congress has been urged to cut the budget deficit, as a way of increasing national savings.

The disturbing little fissure between the blue-collar and white-collar earnings of the old and the young that opened up in the 1980s will probably go away, or at least cease to increase, once America's economic policy has restored its businesses to a level playing field. (Of course, those who were "left behind" for a time in the 1980s will probably never catch up to where they would have been otherwise, much like those who came of age in the Depression.)

None of this has much to do with those who bear the burden of the relatively small tax increases now contemplated by Congress. The "fairness issue," for the representatives who are now adopting every conceivable posture on it, is a scapegoat, as much as affirmative action is a red herring for Louisiana politician David Duke. It scarcely matters who bears the short-term pain of bringing the budget more nearly into balance. What does matter is the truly long-term hurt and humiliation that will attend a failure to get America's fiscal house in order, now.

David Warsh is a columnist for the Boston Globe.