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The biggest guy on the block does have responsibilities the lesser fry may avoid with nobody crying out. So the United States should not be surprised when a convention of its own United Nations Association calls for an upgrading of ''the level of professionalism among US representatives to UN bodies.'' Indeed, the US ought to be an exemplar in this respect.

But really now. The UNA complains that through changing administrations US behavior in the UN system ''has frequently appeared inconsistent, contradictory, and lacking in continuity over the long-term.'' Of how many nations might not the same be said? Maybe some. And certainly the Soviet Union's conduct has in a sense been entirely consistent all the time. But then it doesn't exactly have changing administrations does it?