PERHAPS IT WAS a trade negotiator who first observed that the devil hides in the details. The U.S.-Canadian Free Trade Agreement came before the House subcommittee on trade this week for the first of many congressional hearings. The reception was moderately warm. Everybody was more or less in favor of free trade across the border, in principle. But everybody had an industry -- or two or three -- that claimed to be treated unfairly by the agreement or that had obtained less than it had hoped.

Whether the agreement survives the intricate legislative process here depends on Congress' perspective. If it focuses on the broad benefits to the American economy as a whole, the agreement will get the support it deserves. But if Congress abandons itself to the fears and grievances of the dozen or so industries lobbying against it, the agreement will slide into endless trouble. In this first hearing each congressman took the opportunity to touch firmly on at least one pressure point: eggs (Georgia), textiles (also Georgia), steel (Pennsylvania), television productions (New York), auto parts (Ohio), movie distribution (Illinois), telecommunications equipment (California).

In response, the secretary of the Treasury, James A. Baker, and the president's trade representative, Clayton Yeutter, pointed out that the Free Trade Agreement doesn't really promise to take the two countries all the way to free trade. It will eliminate tariffs, but quite a few quotas and other restraints will remain -- by no means all of them on the Canadian side. In many sensitive areas the agreement provides less than American producers might have expected. But in almost every case it gives Americans better terms throughout the North American market than they now enjoy.

That's going to be the choice for these American industries and for the people who represent them in Congress. Is it better to take half a loaf and establish momentum toward something more, or to kill the whole agreement in the knowledge that it won't be revived in this century?

Ever since World War II the expansion of international trade has been a consistently powerful force for economic growth. The Free Trade Agreement not only would open conventional merchandise trade further but would also establish new rules for crossing the border in services, finance and investment. In a decade in which most countries, including this one, have made more concessions to protectionism than they should have, this agreement would push hard in a healthier and more promising direction.