PROTECTIONISM HAS won an important victory in the Senate, as the trade bill moves slowly toward passage. When imports hurt an American industry, it can ask the president to protect it even when the foreign competition is entirely fair. Under present law, the president can refuse when he finds that protection is not in the best interest of the country. On Tuesday evening, by 55 votes to 41, the senators decided to delete that safety hatch. When an industry is injured by foreign competition, they want it protected whether the president thinks it's in the country's interest or not.

The Senate is at work redefining this country's relationships with the rest of the world. The debate is not just over the technicalities of trade law, nor is it about economics alone. It's about American attitudes toward competition. It's about the social costs of trade expansion and economic growth, and how they are to be paid. Some of these trade votes have been admirable. But this one speaks of an America that is defensive, fearful and uncertain of its own ability to compete.

Since the Reagan administration first came to office, six industries have demonstrated that they were being hurt by imports and petitioned the president for protection. He provided it to four of them -- shingles, carbon steel, specialty steel and motorcycles.

He refused it to two -- copper and shoes. Protection means higher prices, and he pointed out that protection for copper would cost more jobs in the industries using copper than it would save in copper mining. But the Senate's new version of the law won't help the copper miners either, since it contains a specific exemption where protection would threaten downstream industries.

As for the American shoemakers, many are losing their markets to producers abroad who are doing a better job of developing manufacturing technology and staying in touch with fashions. When an industry contributes heavily to its own decline, should not the president be allowed to consider the national interest in deciding whether to shelter it from foreign competition and allowing it to raise its prices?

But the Senate voted that he should not -- that, unless national security is directly involved, protection should be mandatory. Most of the senators who voted that way are Democrats. Of the three Democratic candidates for president who are senators, Albert Gore voted for this protectionist change in the law; Joseph Biden and Paul Simon were absent, but Mr. Simon announced that he supported it. The one Republican candidate in the Senate, Robert Dole, voted to keep the law as it is.

Fortunately, this vote was not the last word. There's no similar provision in the House bill, and in the end it will be up to a conference to settle the shoemakers' grievances -- and American policy toward foreign competitors