In this 40th anniversary year of everything, this week has been devoted to showering hopes and paper praise on the United Nations. The occasion is the convening of the 40th General Assembly. This is one parade that can use some rain.

The original purpose of the United Nations was to promote peace through "collective security." No one even pretends that to be the case any more. It may not be the fault of the United Nations -- the original idea of the Great Powers acting in concert to keep the peace was almost instantly defeated by the advent of the Cold War. Nevertheless, it is a fact. On war and peace, whether in Afghanistan, Nicaragua or the Persian Gulf, the United Nations is irrelevant. Instead, "collective security" has given way to what Jeane Kirkpatrick called the "Turkish bath" theory: the United Nations as a place for nations to let off steam.

If that were all, the United Nations could be written off as an exercise in therapeutic recreation: expensive -- $800 million a year, a quarter of it coming from the United States -- and harmless. Unfortunately, it is not harmless.

Dominated by its automatic Soviet bloc-Third World majority, the United Nations is one of the most important instruments of anti-Western diplomacy. The principal American activity at the United Nations is damage control. One day the United States is blocking a New World Information Order undermining press freedom. The next day it is fighting off Cuba's demand for "self-determination" for Puerto Rico. (Self-determination for Cuba does not come up at the United Nations.) The next day at the Nairobi Women's Conference, the United States is fending off an Iranian delegation, whose women are wrapped in chadors and beyond the reach of irony, condemning America's denial of women's rights.

And when the final communique of the Nairobi Conference merely condemns "coercive measures" by the West against the Third World (and neglects to reaffirm that Zionism is racism) the outcome is deemed a success.

Of such successes a new diplomatic language, UNese, is born. Its syntax and diction are inherently anti-Western. The West pretends not to notice. Western publics ignore the billion pages a year churned out by the United Nations. But for many developing countries, the United Nations and its vast Department of Public Information are an important source of information. With its 65 information centers around the world, it provides the "megaphone effect" for whatever calumny is being pronounced at headquarters.

Regarding one particular calumny, the megaphone does particular harm. The United Nations has become, in the words of William F. Buckley, "the most concentrated assembly of anti- Semitism surely sine Hitler's Germany." In the Security Council, one can hear Israelis referred to as "the Judeo Nazis." In the General Assembly, Jordan's ambassador speaks of the Jewish "cabal, which controls and manipulates and exploits the rest of humanity by controlling the money and wealth of the world." And in 1975 the assembly itself declared that Zionism is racism. Thanks to the United Nations and its information network, it is now a lie heard around the world.

Thanks not just to the United Nations, however. Because what more than anything gives it legitimacy is the participation of the Western democracies. Otherwise its pronouncements would have the weight of a Warsaw Pact declaration.

Why underwrite an enterprise so inimical to our values and interests? At this point one starts hearing about the United Nations' good works. Yes, some of the specialized agencies, such as the World Health Organization, do a wonderful job. But WHO, like some of the etter functioning agencies, pre- dates the United Nations. It was brought into the United Nations system after the war. It lived before the United Nations; it can live after it. And most of the other agencies are distinguished not only by political bias but by simple bureaucratic corruption. UNESCO, for example, is supposed to promote scientific and cultural programs in the developing world. It spends 78 percent of its budget at headquarters in Paris.

The other great good work of the United Nations is peacekeeping. True, there are blue hats in Cyprus and the Golan interposed between warring parties. But it is the parties that keep the peace, not the United Nations. And when one side or the other opts for peace-breaking, the United Nations vanishes. In May 1967, Nasser ordered the United Nations out of the Sinai buffer, the better to make war on Israel. The Secretary General immediately complied.

And there are certain kinds of peace the United Nations will not keep and does not want. It not only refused to supply a peace-keeping force for the 1978 Egyptian-Israeli peace treaty. It has also done everything it can to undermine it. The peacekeeping is done by a non-U.N. force put together by the United States, proving that peace- keeping requires only goodwill and some money, not the Security Council. Another good work survives without the United Nations.

Which leaves the bad works: the destructive propaganda, the anti-Western diplomacy, the anti-Semitism. The United Nations that we are celebrating this week is not the United Nations of Franklin D. Roosevelt and Vandenburg and Cordell Hull. Respect for the noble vision of the United Nations demands that we recognize today's version as a corrupt impostor, inimical to our (and its) ideals and unworthy of our support. Among the pieties of this week's festivities, you won't hear that. But many will think it.