SO THE TENNESSEE VALLEY Authority's Tellico Dam does have to be stopped, on the verge of completion, to save a three-inch fish. That's what the Supreme Court said Thursday in the snail-darter case. The court did not rule that way out of a fondness for the fish. Instead, it found that Congress had settled the issue by writing the Endangered Species Act of 1973 in absolute, uncompromising terms. The darter is endangered; the Little Tennessee River above the dam site is its critical habitat; therefore the law forbids closing the dam. No matter that the project was started years ago, or that Congress has kept providing funds, or that many millions of dollars could be lost if it is stopped. "The plain intent of Congress," Chief Justice Warren Burger wrote for the court, "was to halt and reverse the trend toward species extinction, whatever the cost."

The court's reading is correct.The real problem lies in the law. In our view, "whatever" is too open-ended - and too conclusive - a value to assign to the saving of all species under all circumstances. In saying that, we are not endorsing a heedless trampling on the law or on the flora and fauna it protects. In most cases, experience since 1973 has shown, dams, highways and other projects can be modified - if agencies put their minds to it - to leave critical habitats intact. But where collisions do occur, we think there should be room for public choice. Moreover, that assessment should not just weigh, for instance, the darter against the dam. It should encompass all the benefits and costs of a range of alternatives.

Such a review system is proposed in a carefully drafted bill developed mainly by Sens. Howard Baker (R-Tenn.) and John Culver (D-Iowa). That measure, now awaiting Senate consideration, would establish general criteria and procedures for resolving both the Tellico tangle and future conflicts of this sort. We think that is far preferable to heavy-handed efforts, mostly in the House, to gut the Endangered Species Act or flatly exempt the Tellico Dam.

The Congress is coming late to this essential task of reconciling all the conflicting interests involved. But the task should be pushed through to the end.