(FORTUNE Magazine) – Rush Limbaugh, the AM radio talk show host, is a phenomenon. We know because he tells us so, loudly and often. ''The hottest national radio talk show in the world'' is how he describes his program. ''Conservative and Republican and proud of it'' is how he describes himself. Conservatives, many of whom admire him, feted him in August at the Republican convention in Houston. They lap up Rush stage shows, Rush videos, a new Rush TV program, and now, inevitably, the Rush book, The Way Things Ought to Be (Pocket Books, $22), which currently holds the No. 1 spot for nonfiction on the New York Times best-seller list. What kind of book is it? Judged strictly on its literary and intellectual merits, it is neither particularly bad nor especially good. It's repetitive but not boring. (Limbaugh, whatever your opinion of his politics, is a consummate entertainer). Beyond that, its main value is the fascinating window it provides into the state of orthodox conservatism, circa 1992. What lurks within the hyperactive cerebellum of the AM talk celeb? In two words: Ronald Reagan. If you know what Reagan said, you know what's in this book. Limbaugh shares not only Reagan's views but also his fierce Republican partisanship. At times that produces some delectable contortions, such as when he claims that ''it was the growing number of abortions, year in and year out, that convinced George Bush to change his stand on abortion in the late 1970s.'' Right. He is also like Reagan in one other respect: Liberals who dismiss him as a cretin are underestimating him and will suffer for it. Limbaugh is against animal rights, for example, and lets his listeners know by playing the song ''Born Free'' with sounds of gunfire, explosions, and animal screams ''mixed in for amusement.'' Very funny. Yet his juvenile vulgarity cohabits with dogged thoughtfulness. In the book he argues that rights flow from the concept of mutuality. Animals, he says, ''cannot respect anyone else's rights. Therefore they cannot be said to have rights.'' Nothing buffoonish about that. His abrasive term for radical feminists, ''feminazis,'' is crude and mean, but it also bespeaks an awareness of the authoritarian streak that has disfigured the further reaches of the women's movement. His treatment of abortion is principled and clear, though pro-choicers will disagree with him. His criticisms of environmental hysteria often hit home. At a time when issuelessness is supposed to be the curse of the mass media, Limbaugh positively insists on talking about issues. Finally, when it comes to zinging liberals, Limbaugh has a shrewd instinct for the jugular. He is a populist who understands that some liberals' downfall is their elitism and smugness. He delights in pointing out that activists who claim to be serving high causes are often actually building empires: ''They live well, with a fair amount being siphoned off for expenses, conferences, and high salaries. They survive only by inventing crises or fabricating some threat to an aggrieved minority group.'' So why not anoint Limbaugh a Serious Conservative Thinker, a crank-up-the- volume version of George F. Will? Because living solely to zing liberals -- however much they may at times deserve it -- won't solve many problems. Limbaugh is fond of crowing that ''we are winning'' and that the ''Environmentalist Wackos, Feminazis, Liberal Democrats, Militant Vegetarians, Animal Rights Extremists,'' and assorted other ghouls are a retreating minority. But his incessant complaining about the 1,001 ways liberals have screwed up the country makes you wonder: Just who do these conservatives think has been running the government for the past 12 years? RONALD REAGAN talked about reducing the size of government, balancing the budget, moving toward freer trade, taming middle-class entitlement programs -- and in every case he did the opposite. On social issues, he gave the hard right little more than lip service. As for George Bush, he turned out to be the second-biggest regulator ever, after that notorious liberal Democrat Richard Nixon. By day, Republican politicians rail against government; by night they boast about all the goodies they drag home. Some principled conservatives have begun thinking and writing about conservatism's sellout to the subsidy-for-everyone brand of Big Government. But Limbaugh will have none of it. He prefers to blame liberals, blame Democrats, blame Congress, blame the media -- blame anyone but ''us.'' Case in point: Limbaugh seems to dislike the real estate provisions of Reagan's 1986 tax reform. Whose fault was it? Congress's, of course. Maturity requires acknowledging failures as well as successes. This, Limbaugh and his crowd are wholly unwilling to do. In America, Movement Conservatism has journeyed from its missionary Goldwater-era youth to its agendaless Bush-era decrepitude without ever having grown up.

BOX:

EXCERPT: ''The fact is, there aren't too many funny liberals . . . most liberals are too busy mired in misery and hand-wringing and doing what they can to spread it.''