IT HAS BEEN ALMOST 200 years since the United States first abrogated a treaty. So it may seem strange that no one can be sure whether or not the 1954 mutural defense treaty with Taiwan is about to come to an end. But that's the way it is.

President Carter gave the requisite year's notice last December that the treaty would be terminated on Jan. 1, 1980. But a group of congressmen, claiming the president lacks power single-handedly to abrogate a treaty, challenged him, and they have now won the first round. Federal Judge Oliver Gasch has ruled that the treaty will not be terminated unless Congress takes some action to reinforce what the president has done.

This confrontation between the three branches of government has arisen because the Constitution is silent on how this nation goes about breaking a treaty. Although many treaties have been terminated since the first one (with France) was severed in 1798, there is no consensus among politicians, judges or scholars of the extent of presidential power.

The Carter administration asserts that the president's power over foreign relations gives him the right to abrogate a treaty when he believes it necessary. the administration's chief Capitol Hill critic on this matter, Sen. Barry Goldwater, belives the Senate must approve that termination by a two-thirds vote, just as it must approve a new treaty by such a margin. Judge Gasch ruled that the president's notice of termination is legally ineffective until either the Senate supports him by a two-thirds vote or both houses of Congress pass a resolution of approval by majority vote. Needless to say, the administration is appealing.

There are precendents on all sides. President Coolidge terminated a smuggling treaty with Mexico without congressional participation. President Wilson terminated an internationa sanitary treaty with the concurrence of two-thirds of the Senate. President Taft terminated a commercial treaty with Russia with the approval of both houses of Congress. The result is a legal mess that will not be cleared up until the Supreme Court speaks, if it does. But the court could avoid the whole issue by saying the matter is too political in nature for its intervention.

Given that situation, Senate Majority Leader Robert Byrd is right in seeking some way in which the Senate can vote on the matter. While the treaty with Taiwan is dead for all practical purposes -- and has been since the president acted last December -- it ought to be put of its misery definitively. The only way that can be accomplished before the Jan. 1 termintion date is for Congress to concur in what the president has done.