THE AMERICAN vote against Israel in the Security Council Friday was, in a sense, the essential Carter. There was no good reason of state for the United States to reverse its previous refusal (twice to condemn Israel for expelling two West Bank mayors -- not least because a change would mark its previous votes as politically motivated. Moreover, the issue of the mayors, who are indeed their people's authentic representatives but are also spokesmen for violence, is more complicated than any U.N. majority -- and certainly Secretary General Kurt Waldheim, who immediately offered the mayors the comforts of the house for a hunger strike -- could be expected to grasp. Yet the administration condemned Israel. It evidently did so out of a familiar impulse to be at one with the virtuous souls of the Third World, notwithstanding the complexities of the larger issue at hand.

That issue is whether friends should be treated differently from enemies.It's a tough one. That is, it's a tough one for the United States and especially for the Carter administration. No other country -- no other president -- has so indulged the luxury of deciding whether to support friends on all occasions regardless of their failings or whether to apply ostensibly universal values and condemn them in particular cases when they are deemed to fall short. It would be truly regrettable if the United States followed the pack and decided every case on political grounds alone. At the same time, it cannot be denied that there is a pack and that it hounds Israel shamelessly and that this makes it very serious when the United States joins it. Jimmy Carter has regularly anguished on this score. This time, in perhaps his last U.N. act of consequence, there was a suggestion in the air that he was finally doing what in his heart he has always wanted to do: vote for what he regarded as virtue.

To whatever effect, Ronald Reagan will do it differently. He lacks Jimmy Carter's general readiness to court the Third World and to grant it, or at least its left-leaning part, something of an exemption from the standards by which nations are usually measured. He is unlikely to regard the United Nations as necessarily the most proper and useful forum in which disputes involving the Third World can be treated in the American interest. Few would expect him to agonize at length over the question of whether the United States should keep off Israel's back in loaded global forums, funneling its disagreements into bilateral channels, or whether it should join the jackals, as Mr. Carter did on Friday.