EUGENE McCARTHY took another step yesterday into the realm of the enigmatic, surrendering his seat on the Senate Foreign Relations Committee in order to make room for Wyoming's Gale McGee and indirectly--very indirectly--aid Chairman J. William Fullbright's efficiency schemes. McCarthy's action came as a small shock to his colleagues, including McGee himself. It no doubt also served to strengthen the impression held in not a few quarters that McCarthy has gone over the political deep end.

McGee and Russell Long, whom McCarthy voted last week to retain as Democratic whip, are certainly no tribute to his taste in Senators. Both are hawks on Vietnam, and Long has compiled a pretty objectionable record across the board. McCarthy volunteered explanations for each of these seemingly mysterious acts, but yesterday the logic was a little convoluted and last week it was a little, well, poor. There was truth in McCarthy's contention that replacing Russell Long with Ted Kennedy represented no real step forward in the democratization of the Democratic Party; it was Robert LaFollette who said that half a loaf "dulls the appetite." But since no one was treating Kennedy's election to the whip's post as more than a curious crumb, McCarthy's observation seemed rather short on relevance.

As regards yesterday's maneuver, it may quite possibly develop that McCarthy did the right and honorable thing despite unfortunate side-effects. The full story, if it ever gets out, may even produce a clear and defensible reason for McCarthy's support of Long. But the serenity of the nation's liberal mind will be served if Senator McCarthy soon finds a few clear-cut issues on which to take clear-cut stands.