In the 1860s, a prosperous and confident Great Britain embarked on a crusade to extend the benefits of economic liberty to its continental partners, via a series of free trade treaties.

The venture was somewhat farcical in conception, given that Britain had already unilaterally renounced almost every form of protection, starting with the Repeal of the Corn Laws in 1846, and hence appeared to have nothing to bargain with. Indeed, the British had some difficulty stomaching the reciprocity implied by such a course; Gladstone sniffed that ''a commercial treaty would be an abandonment of the principles of Free Trade . . . if it were founded on what I may call haggling exchanges.''

William Gladstone, meet Richard Gephardt. The Missouri Congressman was once known as an Atari Democrat: the label now seems as false as it is dated. His former neoliberal policies abandoned, his reputation as a backroom dealer buried in phony ''outsider'' rhetoric, Gephardt inspires loathing among the opinion- making ''establishment'' he decries as no other candidate, save Pat Robertson. But nothing attracts such vitriol as the central theme of his candidacy, his retaliatory trade policy, the target of every editorialist with an afternoon to kill.

FUNDAMENTALIST FERVOR

The comparison with Robertson is apt. Gephardt preaches his message with the same fundamentalist fervor, the same random regard for the facts; he draws on the same sense of vertigo, of America in decline. And as with Robertson, the press has reacted to him as if he were some inexplicable evil, a frightening but substanceless phantasm, spontaneously generated. They were wrong about Robertson; they are wrong about Gephardt.

Far from an aberration, Gephardtism is the logical extension of the postwar trade consensus in all developed nations. Trade liberalization has been almost exclusively the product of ''haggling exchanges,'' whether multilaterally, through the GATT, or bilaterally, as in the Canada-U.S. free trade agreement. Outside of Hong Kong and Singapore, the doctrine of reciprocity is everywhere triumphant; no barrier to trade is removed without insistence on like concession from trading partners, and new barriers are met with retaliatory action in the form of countervailing and antidumping duties.

This is a matter strictly of politics, not economics. Theory and experience demonstrates beyond serious challenge that free trade need not be mutual to profit the nation which proclaims it. Indeed, nowhere in 200 years of free market literature will you find the suggestion that tariffs must be lifted in tandem; reciprocity is an invention of mercantilists.

This, however, is thought too sophisticated an argument to tell the children. The public's foggy understanding of trade theory, it is agreed, will make it easy prey for protectionist interest groups. So free trading governments have instead relied on the external constraint of the treaty, using the carrot of export markets and the stick of treaty obligations to appease and muffle the protectionist lobby.

As a political strategy, this has an intuitive appeal; as a matter of economics, moreover, there is clearly greater gain on all sides when free trade is reciprocal. But if, instead, reciprocity retards the process of trade liberalization, then it fails on both political and economic grounds. That is, I would argue, the true meaning of Gephardt's advance.

In most negotiations, each side gives up something of benefit in order to gain something from the other. So negotiating free trade entrenches in the public mind the idea that trade barriers are good for the nation that imposes them, bad for its partners.

If trade is only beneficial when governed by such rules, then trade which breaks the rules, ''unfair'' trade, must therefore be harmful; and if the first rule is reciprocity, then it becomes not only justifiable but imperative that eye for eye be taken, in the interests of ''fairness.'' Once the terms of debate are defined in mercantilist terms, the argument for free trade is lost. Retaliation is then the only logical course. The establishment's jabs at Gephardt's protectionism become as silly as those directed at Robertson's fundamentalism. Everyone thanks God when they win, and prays when they're in danger: Robertson just happens to mean it. Likewise, Gephardt's establishment critics believe in reciprocity, too - but Gephardt means it.

If we insist on meddling in other nations' trade affairs, we would be better placed to strip away all our trade barriers, and threaten selectively to reimpose tariffs on offending countries: policy would then default to free trade in the event of impasse, and we should at least be able to enjoy the blessings of cheap imports while the haggling endured.

Or, we might lower barriers to exports from nations in competition with the offender, in a process of competitive liberalization. But the best course of all would be to reject the false and damaging doctrine of reciprocity, and declare free trade unilaterally.