United Nations, N.Y. — The UN Security Council has reached an impasse over who should be the next secretary-general of the world body. The expectation here, however, is that the five permanent members of the Security Council will get into a huddle and settle on a compromise candidate. And that compromise candidate is likely to be the current secretary-general, the tall and dapper former Austrian foreign minister, Kurt Waldheim.
The low-key diplomat is seeking an unprecedented third term. But, after six rounds of voting, his candidacy has run into a brick wall of Chinese vetoes. The resulting bitterness threatens to undermine his authority even should he eventually be reelected.
His opponent, Salim Salim of Tanzania, has fared worse still. Not only has his support fallen off inside the Council but he also has encountered a persistent United States veto. But since he refuses to withdraw his candidacy, and the Chinese continue to veto Waldheim, the stalemate persists.
What has complicated the process and led the UN Security Council to the present deadlock is the tortuous behavior of several key delegations:
* The Soviet Union's candidate is, beyond the shadow of a doubt, Waldheim. But the USSR has refrained from vetoing Salim for fear of appearing to be less pro-third-world than China.
* China, in supporting Salim even though he has been receiving less than half of the Council's 15 votes, is hoping to show third-world nations that it has their interests at heart. Yet many critics of China charge that its foreign policy is based more on a de facto alliance with the US than on its being a member of the poor nations' club.
* France and Spain, although hoping for a Waldheim victory, have voted both ways in order to collect some good marks with the third world. Both countries reportedly voted for Salim after one especially humiliatingly low vote for him so as to provide him with a slightly larger score next time and, they hoped, a graceful exit.
* The small group of radical countries that launched and organized Salim's campaign seriously miscalculated the depth of the opposition to him. Only two of the six third-world countries in the Council have consistently voted for him.
In particular, the radicals have come under fire here for pushing Salim more as the representative of a specific group - the African group - than as an outstanding world figure.
They persuaded the African group at the UN, for instance, to issue a stern communique calling on the Americans ''to stop vetoing'' Salim and the Soviet Union and Britain ''to stop abstaining.'' Members of the Council, including the Soviet Union, do not look kindly on what observers here call ''a gross interference in the business of the Security Council.''
Although the secretary-general is supposed, by custom, to have a geographic base (European, Asian, African, or Latin American) he was never intended to be the representative of a bloc of nations. He is supposed to be chosen primarily on the basis of his merits, skills, and acceptability to the members of the Security Council.
The impression here is that heavy-handed endorsements of Salim - rammed through by his allies at an OAU and a nonaligned meeting - have backfired and that many member states have become suspicious of him.
The challenge facing the Africans now is to decide whether to support Waldheim (and perhaps pave the way as a result for an African secretary-general five years from now) or to throw their support to any of a dozen Latin American candidates waiting in the wings. But there is little prospect that any of them will simultaneously receive US and Soviet backing.
''What will happen in the end,'' says a well-placed Council member, '' is that the five permanent members of the Council will take matters in their own hands and work out a compromise with each other.'' And to two other members of the Council the name of the compromise is likely to be Waldheim.
Meanwhile, emotions are running high and the growing polarization between ideological and geographical groups threatens to tarnish the institution itself.