GEORGE BUSH, addressing the 46th annual session of the United Nations General Assembly, underscored the new responsibilities being loaded on the world body.Mr. Bush called for more determined enforcement of all resolutions regarding Iraq. This could involve warplane escorts for the UN personnel investigating Iraq's chemical and nuclear weaponry. As Bush spoke, UN inspectors who had uncovered documents outlining Iraq's nuclear program were being detained. The US president also asked the General Assembly to take up another kind of responsibility: repealing its 1975 resolution equating Zionism and racism. Bush rightly pointed out that the resolution is at odds with the mission of the UN to work impartially for peace in all regions of the world. It should be jettisoned. Pressures, meanwhile, are mounting for some form of UN intervention in Yugoslavia. The European Community has tried valiantly to quell the violence. If the latest cease-fire holds, the EC plan for a negotiated settlement may yet get off the ground. The UN's preference is to let the regional body lead the peace effort. But if the Yugoslav friction continues, the UN Security Council may have to address the conflict, with its potential for entangling neighboring countries and generating huge refugee flows. Yugoslavia, like Iraq, could push the UN into the uncomfortable position of trying to prevent the abuse of minorities within a member country crisscrossed by ethnic fault lines. Membership itself is a hot issue. Seven new UN members were ushered in last week, including the two Koreas and the three Baltic states, marking a kind of post-cold-war watershed. Among former Soviet republics, the Baltics had the distinction of long and widely recognized claims to independence. Owing to Stalin's scheming, the Ukraine and Byelorussia have always been UN members. But what about the other republics? Their claims to membership should prompt some hard thinking about genuine sovereignty - especially since a semblance of central coordination, if not control, still exists in Moscow. The disappearance of Soviet power leaves something of a vacuum at UN headquarters, with questions arising over who will ultimately claim the Soviets' veto power in the Security Council. But the present setup is likely to change only gradually. There's too much coming at the UN from outside right now - continued problems with Iraq, coming elections in Cambodia, Salvadoran peace hopes, Middle East hostage negotiations, and maybe Yugoslavia - to risk a major shake-up on the inside.