MUSHROOMS? First it was the steel producers, bitterly claiming - with a bit of exaggeration - that they were being pushed to destitution by brutal and predatory foreign competition. Then it was the shoemaker, closely followed by the sugar producers and the people who make television sets. Now it's the mushroom canners who are pounding on the White House door and crying for protection from their competitors in Taiwan and South Korea. You might ask what's going on here.

Actually, it's a delayed reaction to a chain of events starting six years ago with the devaluation of the dolar.

Devaluation meant that this country could sell more abroad. In turn, it began to buy more. From 1971 to 1974, U.S. imports shot upward from $46 billion worth of goods a year to $104 billion. There wasn't much political reaction as long as the economy was strong, but then came the recession.

Imports have not increased much in relation to the U.S. economy as a whole since 1974. But in that year Congress passed the Trade Reform Act - which this newspaper, incidentally, vigorouly supported. As we have seen discovered, we were dead wrong. The act contains provisions capable of turning the new International Trade Commission into a haven in which every sort of protectionist can find aid and comfort. A domestic industry doesn't have to prove that its foreign competiton is unfair, or that it's unhealthy. The domestic producer has only to show that it is being injured by imports to obtain sweeping recommendations for remedies like tariffs and quotas. The current flood of protectionist appeals and litigation means that Washington lawyers - and ourselves - are coming to see how the Trade Act can be used. The trouble with this kind of litigation, as method of making trade policy, is that it never takes into account the people who produce for ecxport. But they will be the first to suffer when foreign governments retaliate against U.S. imports quotas.

There's still another past event that's now deranging trade: the great rise in oil prices. This country's trade deficit for 1977 will be well over $20 billion, three times the previous record. But the U.S. deficit on imported oil alone will run over $40 billion. All of on imported countries are jostling each other in the marketplace as they attempt not only to protect jobs but also to pay for their oil imports. Mushrooms are not a large item in world trade. But the small cases become the precedents for the large ones. The warm-hearted International Trade Commission has twice recommended protection for the U.S. mushroom canners. Both President Ford and now President Carter have refused it. They are right, of course.

But the paradox remains: The properity of every rich nation depends crucially on world trade, yet in each of them the anxious struggle for jobs, oil and wealth leads to rising assaults on the flow of trade. The aggrieved and litigious mushroom industry won't be the last to press its case.