THE COURAGE OF A CONSERVATIVE. By James G. Watt with Doug Wead. Simon and Schuster. 221 pp. $15.95.

NOW AS EVER, political celebrity tends to get confused with intellectual authority. That is presumably why James Watt, a man with interesting tales to tell, felt called instead to share with us his views on "modern conservatism." As Ronald Reagan's secretary of the interior (1981-84), Watt was mainly noted for saying odd, sometimes silly things -- such as that Indian reservations are revealing examples of socialism at work. But now he has set aside his jesting to prophesy solemnly upon conservatism.

There is, however, a slight problem. Watt is not, by any useful or traditional definition, a conservative. The proof is that he believes "we conservatives are revolutionaries." And while it may be tru that his own brand of conservatism is revolutionary, as a rule conservatives, properly so called, are people who seek by timely adjustment of traditional values and institutions to prevent revolutions, not perpetrate them.

If Watt's taste for mild upheaval disqualifies him as a traditional conservative, what then is he? His views strike me as a variation on a familiar American political theme, prairie populism. Whether of the right or left, prairie populism has certain enduring earmarks. It smacks of the wide open spaces where a verity is a verity, and is usually cranky, idiosyncratic, and not over-scrupulous in its attention to historical fact. Under this rubric, Watt qualifies; but that is a mere quibble.

Here is how his system works. Whatever Watt finds disturbing -- for instance Supreme Court rulings against school prayer -- he blames on a set of faceless adversaries known collectively as "the liberals." They are Watt's Smersh, the political anti-force. "The liberals" constantly appear and reappear throughout this book, but are never identified by name or allowed to speak for themselves. As made-to- order straw men they can be assigned whatever daffy or outrageous views the author wishes to attribute to them. It is a bit like Geoge Orwell's Animal Farm, in which the ruling pigs decreed: "Four legs good, two legs bad." Here, "liberal bad, conservative good." Sound simple? It is.

Not that Watt doesn't from time to time make sense of a sort, as for instance when he criticizes television violence. But his "philosophy" is mostly a matter of taste, being more usually proclaimed, like a religious doctrine, than argued from consistent or recognizable first principles.

The truly disabling flaw of his outlook is not that his views are especially extreme or disagreeable. It is his unmanageable compulsion to polarize every issue along a liberal-conservative axis -- a tiresome habit of discourse common to ideologues of both right and left.

For instance, he writes: "Liberals often oppose conservative ideas such as stiff penalties for drunk driving." Is he suggesting that our permissive attitude towards highway deaths caused by drunkenness is an ideological issue? If so, would he also say that "conservative" opposition to the 55-mph national speed limit (See the 1980 Republican platform) is also objectionable? Ideology seems here a poor instrument of analysis.

Watt likewise resorts to the same inappropriate polarization in dealing with a more complex issue -- U.S.-Israeli relations. He correctly notes the strategic usefulness of Israel's military power. But what does it mean to say that "the extreme commitment of modern conservatives to Israel disturbs many liberals"?

One gathers that Watt is one of those Biblical fundamentalists who share with Menachem Begin and other Israelis the view that Jahveh once promised the whole of historic Palestine to the heir and assigns of Abraham: a view to which many Israelis, to say nothing of Arabs, object. Is this what is known as an "extreme commitment," and if it is how far does it go before worry is justified? A green light for the annexation of the West Bank and Gaza? Endorsement of Rabbi Kahane's racist view that the only good Arab is an expelled one?

IN FACT, there is no evidence that approval or disapproval of Israel, or Israeli policies (the two are, after all, distinguishable in important ways) runs along some ideological fault line dividing "liberals" from "conservatives." Consider, for instance, that until it became a liability for him in his 1984 fight for Senate re-election, that paladin of modern conservatism Jesse Helms was very anti-Israel. Conversely, it would take all the toes and fingers in Tel Aviv to count the eminent American liberals who are hawkish in support of Israel's interests, if of no other.

But it is pointless to fret very much about such inane formulations, for as Watt demonstrates, he knows considerably less than all about the Middle East or its (non-Biblical) history. Otherwise, he would not speak of a "Truman Doctrine for the Middle East," when he presumably means the Truman Doctrine for Greece and Turkey. Getting the thing vaguely placed in the eastern Mediterranean is not quite the same as knowing what you're talking about.

If these lapses were rare, it would be pedantic and trifling to mention them, but the truth is that they are chronic in this book. For example:

Item: Watt argues that blacks and conservatives got at cross purposes 20-odd years ago because Barry Goldwater, running for president, stood for states rights, his stand attracted southerners and some of these recruits were racists. "The consequences," he writes, "were tragic, both for blacks and for conservatives."

This is a recurrent theme in the official Reaganite view of civil rights. If only blacks were discerning enough to see their real interests, how they've been defrauded by liberals and would be helped by conservatives, they would flock to the GOP banner. But Watt, as usual, omits a critical fact. Any useful history of the black-Goldwater relationship -- and whatever persistent alienation from "modern conservatism" stems from it -- must begin with the senator's strenuous opposition to the 1964 civil rights bill -- legislation of epochal symbolic and practilcal importance to blacks. That Goldwater's opposition probably had nothing to do with race does not help. No such "conservatism," however principled, is likely to win the loyalty of black Americans.

Item: In a confusing reference to the Supreme Court's 1966 Miranda decision on the rights of the criminally accused, Watt speaks of Miranda as having been "set free." Perhaps he was, but it seems not to be well understood that when a criminal sentence is overturned the culprit may be, and often is, rearrested, retried, and reconvicted.

ITEM: ON PAGE 106 there occurs the remarkable assertion that "18th-century French philosophers had taught that liberty and religion were natural enemies." If Watt means the philosophes, the statement as it stands is grossly unhistorical. Many such "philosophers" were, in fact, clergymen and saw no fixed enmity between liberty and religion. They were hostile to institutional forms of religion that seemed to them oppressive or inquisitorial. (Cf. Voltaire, Rousseau, Diderot, D'Alembert, et al.) It happens that Watt and other "modern conservatives," who think that we are less moral than we should be or used to be blame court-promoted "secularization" and find it handy to confuse the separation of church and state with hostility to religion. A misreading (or misrepresentation) of 18th century attitudes is useful.

In all 205 pages of this tract, I detected only one instance in which Watt's tireless attitudinizing seemed to be at all informed. The chapter on the farm problem, in which he deplores government subsidies and calls for a free-market agriculture, may be wrongheaded, but it shows some knowledge of the subject, and in that it is exceptional.

Why then, one finally asks, does a man of some liveliness of mind and good cheer ignore his riotous days at Interior and plunge, instead, into murky issues that are, in sober truth, beyond his depth? It is, I think, the pernicious assumption that a little brief authority confers wisdom. Of that old illusion, James Watt is not the first victim.