The United Nations has enough problems to overcome as it is. So it is doubly saddening that it is bogged down in a struggle over the selection of a secretary-general. In theory this office should be chosen on the basis of personal merits and of political acceptability to the members of the Security Council. But strong-arm tactics by third-world parties in support of Tanzanian candidate Salim Salim and China's hard stand against an unprecedented third term for Kurt Waldheim - out of pique at US policy on Taiwan - have combined to produce a deadlock. The urgent need is to find a way out of it.
Now that both Mr. Waldheim and Mr. Salim have withdrawn their candidacies (but not their availability), the way is clear for consideration of a number of other aspirants from the third world. It remains problematic that any of the five new candidates in the contest will win approval of the Security Council. But there is no question that someone like Shridath Ramphal of Guyana, secretary general of the Commonwealth nations, would be a superb choice. Certainly one can sympathize with the majority view at the UN that it is time for someone from among the developing nations to head up the Secretariat again. The industrialized ''North'' has no corner on capable diplomats and administrators and it is only fair that the office be rotated geographically.
That is the ideal, however. The difficulty is that nothing can be done at the UN outside of the context of the East-West balance of power. The organization was in fact set up to take account of superpower interests, for without doing so it could not function at all. In this instance the nations of the ''South'' perhaps have pressed their case too far. Realistically there is no chance the Reagan administration would ever accept Mr. Salim (who humiliated the US at the time the Chinese Communists were seated in the UN General Assembly). All that the present turmoil does, therefore, is to weaken the UN and fuel the general indifference with which the Reagan administration already views the international body. That is hardly the way for the third world to engage President Reagan's interest.
It will be splendid if one of the new contenders makes the grade in the Security Council. The UN would then have a needed fresh public voice. Kurt Waldheim in his two terms has performed well and, within the narrow limits of his power, accomplished more than generally given credit for. But the widespread opposition to him and the present bitterness over his candidacy means that his effectiveness would be diluted even more.
If the Security Council cannot pull together on a new candidate, however, it will have to act quickly to avoid plunging the UN into a crisis - leaving it without a leader in the new year as the General Assembly (which is supposed to approve the Security Council appointment) winds up its session and goes home. The best solution in such case would be an interim one-year or two-year reappointment for Mr. Waldheim with an understanding that his successor would be from the third world. Experienced and knowledgeable, Mr. Waldheim would ably carry on while the Soviet Union and the United States studied the matter and settled on someone mutually acceptable.
Eleventh-hour decisionmaking in the Security Council should not prevent cool reasonableness from prevailing.