United Nations, N.Y. — Participants in the General Assembly session of the United Nations now drawing to a close are divided over its relevance and impact.
Pessimists who saw the session as ineffective, dispirited, morose, and even futile view the UN diplomatic glass as half empty.
''No progress was accomplished on any of the major issues: Afghanistan, Cambodia, the Middle East, Namibia, the Iraq-Iran war, disarmament,'' says a Western ambassador. ''Repetitious speeches, repetitious resolutions, all to no avail,'' laments a US diplomat.
Optimists who attribute the UN's present circumstances to world conditions beyond its control see the glass as half full. Those inclined to a more positive view are encouraged at least by the UN's willingness to examine itself, a willingness they say may strengthen the role of the organization in the future.
Also on the more active side:
* The conceptual effort carried out as a result of UN Secretary-General Perez de Cuellar's annual report, regarding the collective security system, and the new vigor lent to the reformist movement within the UN (aimed at lessening the control the five permanent members of the Security Council have over the organization through the use of the veto).
* The emergence of Latin America, until now a sleeping giant, at the UN. Latin America stole the show from the Arabs and the Africans and occupied the center stage with the Falklands debate, Nicaragua's election to the Security Council, the debate over whether Christopher Columbus or someone else first set foot in the New World.
* The ongoing and growing debate among third-world countries, especially among Latin American countries, regarding human rights. Both a Cuban-sponsored resolution stressing social and economic rights and a Western resolution stressing individual rights were adopted.
One good surprise: ''Common sense prevailed, and the third world knew better than to deprive Israel of its rights under the Charter,'' an observer says.
Most observers here agree the UN is in trouble, but that its weakness may be only temporary.
The ambassador of a pro-US and conservative third-world country echoes the opinion of others:
''When both superpowers are fighting bitterly for every square inch of the diplomatic chessboard, there is no room for smaller, weaker nations to follow an independent course. It is obvious that neither the US nor the USSR are interested in multilateral diplomacy at this time.
''In the final analysis,'' he continues, ''whether the UN plays a strong role or not rests on US attitudes toward it. When the US is behind the organization, the smaller nations follow suit and the USSR has then no choice but to march in step. To sum it up: Everybody here, friends of the US, adversaries, nonaligned, all believe they must sit out the Reagan administration and wait for better days.''