THE United Nations broke free of a hobble this week by revoking its 1975 resolution equating Zionism with racism. That resolution attempted to impugn Israel's legitimacy, but only succeeded in excluding the UN from any effective role in the search for Middle East peace.As the offspring of a marriage between Arab rejectionism and Soviet-bloc opportunism, it was another cold-war relic, rightly discarded. The General Assembly's reversal of its earlier vote reflects the world's yearning for an end to the long cycle of Middle East violence. True, many Arab states stuck by their 1975 vote; others showed a degree of moderation by abstaining. But the 111-25 tally revealed an unmistakable readiness on the part of most nations to junk the old polemics. They recognize that a constructive stance must combine Israel's right to security and recognition, the Palestinian right to self-determination, and a just resolution of the territorial questions left over from the 1967 conflict. The UN action will do little to solve the problems developing in the current Arab-Israeli negotiations. But it at least removes one cloud that has hung over Middle East peacemaking. Sadly, plenty of other clouds have been gathering. Most ominous, extremists on both sides are resorting to violence. Palestinian radicals, representing the minority who never wanted the talks in the first place, have taken to shooting and tossing grenades. Israeli settlers in the West Bank have rampaged in revenge; Arab dwellings in East Jerusalem have been seized by Israeli religious fanatics. Israel's government, typically, has cracked down hardest on Palestinians, with night-time curfews and other mea sures. None of this is a surprise. The extremists will do what they can to thwart peace. The people who've been meeting in Washington, meanwhile, should do more to advance peace. The Palestinian demand for separate talks with Israel is understandable. It shouldn't stand in the way of substantive negotiations. The Palestinian interests will certainly by represented even if Jordanians join them in initial phases of the talks. Likewise, the Israeli inclination to focus on where talks should next be held is an unnecessary obstruction. It may not be a bad idea to shift talks closer to the region eventually. But that concern shouldn't be allowed to gum the works now. The United States could try to break this impasse. But the parties ought to be able to do it themselves. It's a test of their commitment.