(FORTUNE Magazine) – ''Who did this to us? Who stole our standard of living?'' According to high-minded Bill Moyers of Public Television, these are the questions the next generation of Americans will ask. Bill fears the questions will come too late, however. In a long interview with the Washington Post, much of it given over to denials of his presidential ambitions, he worried sardonically that ''Ronald Reagan will be up on Mount Rushmore and George Bush will be carved into the stadium at Texas A&M before the next generation wakes up.'' Bill is not the only liberal breathing hard these days about the country's collapsing standard of living. House Majority Leader Dick Gephardt says declining living standards are the ''overarching issue'' of our times. Presidential hopeful Tom Harkin of Iowa says the middle class is seething over what he calls the 20-year stagnation of real incomes. Hopeful Paul Tsongas of Massachusetts turned up in Texas the other day commenting that he could carry the Lone Star State if the issue was ''restoring the American standard of living.'' The issue got an extra working over on Labor Day, when numerous dirigiste commentaries linked declining living standards to (a) declining union strength and (b) Reagan-Bush economic policy. An ''editorial backgrounder,'' issued by Gerald W. McEntee of the American Federation of State, County, and Municipal Employees in connection with the unions' huge Labor Day march in Washington, proclaimed that living standards collapsed in the Eighties because of Reagan- Bush policies favoring the rich. Representative Sander M. Levin of Michigan got quoted in the New York Times on Labor Day as stating that lowered living standards were ''the Achilles' heel of the Republican party.'' Victor Gotbaum, long a union big shot in New York and now in the professor business at City University, also turned up in the article averring that ''the standard of living is the valid issue'' (and arguing that it was up to the unions to do something about it). Times reporter Peter T. Kilborn quoted various liblab economists as making similar points, and his article was accompanied by a chart in which, sure enough, the people were doing great in the Fifties and Sixties but slipping in the Seventies and Eighties. Have living standards really collapsed? People who answer yes are fond of citing the Labor Department series used for the Times chart: average weekly earnings, in constant dollars, of nonsupervisory workers in private industry. These data show an 8% decline in the Seventies followed by another 5% decline in the Eighties. But as measures of living standards, the data are highly deficient. One problem with them is that the charted decline was to some extent quite desirable: It reflected the collapse of union monopoly wage scales all across the U.S. industrial landscape. In the late Seventies, for example, unionized steel and auto workers were still earning premiums of around 85% over the manufacturing average. You could argue that, whatever the reason, those workers have lower living standards now; but their lower standards are a gain for consumers who once paid the premiums in the form of higher prices. The weekly earnings series is a rotten measure for other reasons. It excludes the earnings of government workers, farm workers, managers at all levels, and the self-employed. Furthermore, the data are pretax. A far better and broader gauge would be the Commerce Department series on real disposable income per capita, which shows an increase of 41% during 1970-90. Our own preferred measure of living standards is consumption, not earnings. , Per capita consumer spending, in constant dollars, rose fairly steadily in both the Seventies and Eighties. Gain for the Seventies: 21%. For the Reagan- Bush Eighties: another 21%. Average annual increase over the 20 years: 1.9%. Will any such findings get mentioned in the Democratic primaries? One somehow doubts it, does not one?