STEVE FORBES is no slave to fashion. In 1996, when the religious right looked strong, he disdained its favorite issues during the Republican primaries. Now, when moralists look weak, Mr. Forbes is pandering to them. In 1996, when Americans worried about rising inequality, Mr. Forbes proposed a flat tax that would have made the problem worse. Now, when just about everyone applauds the Federal Reserve, he attacks it.

This latest outburst, occasioned by the Fed's decision to raise interest rates a quarter- point, puts Mr. Forbes in some surprising company. Fed-bashing is a sport traditionally practiced by the populist left. A generation ago Wright Patman, a prairie Texan far removed from Mr. Forbes's country-club origins, delivered stem-winding attacks on the central bank, accusing it of indifference to the poverty of his constituents. These days Sen. Tom Harkin, populist of Iowa, complains of "the highest real rates of interest that we've had just about in my lifetime," having apparently suppressed all memory of the early 1980s.

Mr. Forbes likes to present himself as the candidate of substance, in juxtaposition to the allegedly lightweight Gov. George W. Bush of Texas. His argument in this case is that the Federal Reserve is tracking the wrong indicators: It focuses on the unemployment rate rather than on commodity prices.

Yet this is a bizarre claim. In a modern economy, commodity prices are hardly the best indicator of coming inflation; the price of legal advice or computer chips may quite possibly be better. Moreover, the Fed is not particularly hung up on the unemployment rate, whatever Mr. Forbes might say. It seeks to anticipate inflation by watching for a wide array of warning signs, ranging from capacity utilization in commercial trucks to the rate of new home building.

Mr. Forbes ought to remember that Fed-bashing seldom does much good. Either criticism is ignored, in which case the critic looks foolish. Or it is taken to heart, in which case the Fed's reputation for standing above the political fray is damaged -- and this in turn means that investors expect more inflation, and so drive interest rates upward. Mr. Forbes's fondness for policy substance is admirable in theory. But America will do just fine without this particular example of it.