Of all the differences between Labor Day 1930 and Labor Day 1990, among the most striking is this: The characteristic organization, the urgent voice then, was the labor union. The characteristic organization today is the think tank.

That is not to say that unions are finished -- far from it. They seem to be slowly regaining their purpose and redefining their role. But where newspaper reporters once flocked to hear what John L. Lewis or David Dubinsky thought about the Hoover administration's latest initiative, today "The McNeil-Lehrer Report" amplifies the views of policy analysts, usually economists or political scientists, drawn from a dozen contending centers of learning.

How this came about will some day make a fascinating tale. There are more streams of thought that run together to form the present-day turn to the right than anyone can easily guess.

Inside Washington's Capital Beltway, the American Enterprise Institute and the Heritage Foundation may seem the alpha and omega of the movement. But before there was George Mason University, there was the University of Chicago; and before there was the semi-scholarly quarterly the Public Interest, there was the Institute for Economic Affairs (IEA).

Founded in 1956 by conservative businessman Antony Fisher, the IEA was the first of those organizations to operate on the boundary between university scholarship and public policy that have become so familiar and powerful today. The story of the IEA is laid out in an agreeable, first-person fashion in "Capitalism" by Arthur Seldon (Basil Blackwell, $29.95).

Seldon is the man who for 30 years was editorial director of the IEA. "Capitalism" sums up the long assault on socialism over which he presided. Long before it was fashionable in America to soften up the opposition with the "artillery" of principles in preparation for the "infantry" of policy implementation, Seldon was commissioning double-domes to write for the public in his famous series of Hobart Papers.

What a remarkably shrewd judge of academic horsepower he was: Friedrich von Hayek, Milton Friedman and James Buchanan were IEA mainstays before they were widely recognized.

It is not too much to say that the IEA approach is responsible for the distinctive intellectual style of Thatcherism, now being consciously echoed in places as far-flung as Czechoslovakia, Peru and the Soviet Union.

The major points of Seldon's argument will be familiar to anyone who has followed ideological politics, even casually, in this country since the election of Ronald Reagan. Indeed, the book itself is a kind of catechism for advanced readers:

The market is to be preferred to the political process because it allows individuals to express their judgments and preferences as individuals, "without going through the political filter of majority (or largest minority) approval."

"Private property is the indispensable requirement for the individuals to learn the lessons of responsibility by benefiting from success and suffering from failure."

"Competition is essential to enable consumers to compare and contrast alternatives. Under socialism, a single supplier excludes comparison and cannot claim superiority. No one can know if a monopoly, state or private, offers the best since it is the only source."

"Since government is inherently inefficient in hitting targets, it gives itself the benefit of the doubt. It overshoots where it is politically easier than to undershoot, and undershoots where it is politically easier than to overshoot. It tends to over-regulate industry because the risks of under-regulation (as in medicines or financial services) are more apparent, but the public interest is better served by under-regulation, which proliferates alternatives."

"It tends to overtax covertly where possible because it is more popular to reduce than to raise taxes, but the public interest prefers under-taxation. It tends to inflate its powers covertly because it is easier to relax than to expand them, but the public interest is served more by too little than by too much government."

How did these tenets, which can be said to have underlain the Republican victories in the last three elections, come to be so widely accepted in 1990? Surely they were not widely subscribed to in 1930, although they were widely proclaimed. According to the writer Joseph Alsop, one of the richer members of the Du Pont family wrote Franklin Roosevelt in that year to announce that "now he knew for certain the foundations of the Republic were crumbling away, because five black workers on his South Carolina quail plantation had just rejected wages of one dollar a day on the shocking ground that they could get a bit more from the Federal Government in the form of relief."

The answer seems to be: experience. Those field workers in South Carolina were only too happy to move to Detroit in search of $5-a-day wages from Henry Ford.

Those socialist countries that tried without success to jump-start their economies with a "big push" found that Ludwig von Mises and Hayek had been right all along -- command economy simply couldn't do without the information conveyed by a price system, much less produce a widespread sense of initiative and responsibility among their citizens.

Though there is much interesting analysis and exposition in Seldon's book, there is probably nothing quite so persuasive as the sentimental little coda. In this last section, Seldon relates how at age 11, when he moved away from his gas-lit house in London's poor East End, with "its single cold-water tap and lavatory in the yard" he vowed to return one day with a motor car to give his childhood chums a ride around the block.

It wasn't necessary, Seldon writes. Most grew up to own motor cars before he did. Many did quite well under capitalism, he relates. There were corporate chieftains, small business proprietors, university dons, middle-class professionals.

The neighborhood next door even produced an English lord, Chapple of Hoxton, who provides a jaunty little forward to the book. But before he was Chapple of Hoxton, he was Frank Chapple, head of the electricians union from 1966 to 1984.

If you want to know what happened, you should read Seldon's book.

David Warsh is a columnist for the Boston Globe.