Talk of accelerated depreciation is on every tongue, except those tongues talking about some other aspect of tax reform. Reform, spreading fear in gilded mansions and hope among toiling masses, has the public's attention.

Or, more precisely, it has the publics' attention. Note the placement of the apostrophe, which tells the essential truth of American politics. On an issue such as tax reform, the public (definite article, "the") is a fiction. There are lots of little publics with rival interests. Another problem is that the tax reform drive opens with a dubious moral pronouncement and a suspect empirical claim.

The moral point is that "the public" believes the tax system is unfair and the public's perception must be accommodated. Actually, polls show that the "unfairness" of the system is a low-intensity grievance. Besides, unhappiness about the tax system is being assiduously cultivated, not least by Republicans eager to change the subject from the deficit to . . . well, anything.

The empirical claim is that a flat(ter), simple(r) tax with business taxes increased will facilitate growth. That may be true, but no one can know that it is, and recent events -- conjunction of tax cuts and mushrooming deficits -- should have administration prophets feeling chastened.

Some Republicans think their tax reform will stimulate growth because that is the way the world works, assuming that God was reading the right economics text when he designed the world. That is, the economy should work best when government works least at influencing the flow of forces, using a finely tuned tax code.

Many Republicans deplore "people who view the tax as a means of advancing changes in our social structure." Those words were in a speech delivered by a private citizen, in 1964, in support of Barry Goldwater. Ronald Reagan has gone on saying that. (In 1981: The tax power "must not be used to regulate the economy or bring about social change.") He will go on saying it as he praises a tax plan that includes tuition tax credits to improve the educational system, special tax treatment of businesses in "enterprise zones," special rates to encourage small businesses, provisions to nurture energy supplies, increased personal exemptions justified as "family policy" and so on.

Let social goals influence tax policy? Heaven forfend. But it is possible to view the proposal to end the deductibility of state and local taxes as the second punch in the one-two of Reaganism.

The first punch was the 1981 vote for tax cuts that shrank the revenue base of the federal government. This produced a dangerous economic fact, the deficits, and a stunning political result: it changed the political conversation of the country, perhaps for a generation. This year's House and Senate budget resolutions differ about many things, but not about the central thing. They agree that the issue is not whether but where to cut spending.

Reagan altered the federal agenda by shrinking federal resources, and now he proposes to restrain state and local government by altering a line in the federal tax code. Ending the deductibility of state and local taxes will increase the real burden of those taxes on payers. This will alter the taxing and spending environment in which state and local politicians operate.

The administration will defend in terms of economic efficiency the proposal to increase the tax burden on business. But the proposal involves political calculation and failure of nerve. It would take uncommon nerve to act on Reagan's reiterated and correct belief that, because we do not know who pays business taxes, they might well be abolished. Anyway, "populism," which is suddenly in vogue, involves saying General Motors must pay its "fair share" so grandma can pay less.

Liberals traditionally talk as though they can pluck from thin air the indisputable truth about the "fairness" of everything. Conservatives should not compete on that field. Rather, they should earn respect by results born of realism. But "populist conservatism" is the wave of the future, this week. Populism historically involves impatience with complexity, suspicion of big institutions and big people, and reverence for whatever "the people" are thought to believe this week. So "populist conservatism" is an oxymoron.

Treasury Secretary James Baker recently told an audience that tax reform is rooted in populism, which is "opposed to elitism, opposed to excessive concentrations of power and oriented toward fairness." Baker's call to egalitarianism was well received by his audience, the Houston Chamber of Commerce, which peered under the tables and behind the potted palms to make sure no elites were lurking.