WHEN the United Nations General Assembly convenes again this month in New York for its annual session, United States attitudes toward the world body will once more be tested.In the wake of the Gulf war in which the UN Security Council supported US initiatives, previously negative American attitudes toward the UN abated. The Gulf war experience has been followed by the active involvement of the UN, primarily through its secretary-general, Javier Perez de Cuellar, in efforts to settle significant regional conflicts in Cambodia and El Salvador and to assist in resolving the hostage crisis in Lebanon. These have been viewed positively in Washington, but this could change as the result of two developments in New York: the reconvening of the General Assembly and the election of a new secretary-general. The General Assembly, with its third-world majority, has in the past been the principal arena for statements and actions that have particularly angered congressional and other US opinion. A congressionally-mandated annual report documents General Assembly actions that have been generally unfavorable to US official positions - primarily on issues related to the Middle East and Southern Africa. Members of Congress and others incensed by such findings have not drawn a distinction between the General Assembl y - which has only recommending power - and the more authoritative Security Council in which the US has the veto. As a result, American attitudes toward the UN as a whole have suffered. The General Assembly is also the forum for the annual debate on foreign policy during which world leaders - including the president of the US - traditionally address the body. These sessions have at times in the past also been the vehicles for strong anti-American statements - with consequent adverse reactions in Washington. It is likely that with the end of the cold war and changes in South Africa the General Assembly debate will be less provocative in American eyes. The unresolved problems of the Middle East and the Palestine issue, however, could still be raised in ways that complicate US policies and peace efforts in the region. Future attitudes toward the UN will also be determined by the outcome of the election for a new secretary-general to succeed Perez de Cuellar, whose term ends Jan. 1. The General Assembly will recommend a candidate for formal selection by the Security Council. Two issues will emerge: the acceptability of the candidates to the US and whether selection should be by rotation of regional blocs. The US, as of this writing, has not declared its support for a particular individual, but Washington will obviously favor a candidate with whom the US can work comfortably. African member nations believe the time has come for the appointment of a UN secretary-general from Africa, and several candidates have been put forward. They argue that past secretaries-general have come from Europe (Dag Hammerskjold, Trygvie Lie, Kurt Waldheim), Asia (U Thant) and Latin America (Perez de Cuellar) and that it is time for an African secretary-general. The US, however, has not conceded that the secretary-generalship should be determined by regional rotation and may prefer a candidate from another region. The possibilities of differences with the Africans loom with domestic US as well as foreign policy implications, public and congressional opinion. Over the years of its existence, the UN has served US interests in many ways. The resolutions of the Security Council have laid the foundations for peace, even if the Council has been unable immediately to resolve disputes. Antagonists could meet under UN auspices in New York when no other venue seemed politically possible. The UN specialized agencies have carried out work the US could not do. Yet attitudes in the US toward the organization have been molded not by these positive aspects but by the highly charged and publicized rhetoric of voices in the General Assembly and the perception that the US does not have sufficient control over UN actions. Differences over the UN budget led the US to withhold funds; Washington has been in arrears in its UN obligations and is only now beginning to settle its debt. In the early 1980s, some conservative groups even recommended that the US withdraw its me mbership. The forthcoming General Assembly session may reflect the more moderate trends of the post-Gulf-war period, but even if it does not, too much is at stake for the US once more to turn its back on the UN. The United Nations and its secretary-general are playing a significant role in resolving international issues. These efforts are clearly in US interests. It would be tragic if peripheral rhetoric in the General Assembly or disagreements over the new secretary-general set back today's favorable view of the UN in the US.