An extraterrestrial inspector general of Earth's last, great hope for peace would have to be wondering what in the Universe is going on here. Even the Arabs who know better have been lining up sheep-like behind efforts to disenfranchise Israel. The United States has been issuing daily warnings that it will pick up its money bags and walk out of the United Nations with the Israelis, if it comes to that.

Things have gotten so spacey that some folks are even suggesting that this would be good news. The United Nations would be left to stew in its own rancid juices. Wheeling and dealing directly with the world's conflicts and confrontations, the United States would be master of its fate. No loner would it suffer the disproportionate power the U.N. gives tiny-to-medium- size, newly emerged nations; the double standards; the moral bankruptcy so often displayed not only when the issue is Israel.

It sounds like welcome relief, until you talk to some of the old hands here. Unlike the transient envoys who represent the members, the sloggers in the permanent bureaucracy have a special sensitivity to the U.N.'s assets as well as its liabilities. They know to what extent this world institution is a mirror image of the sometimes zany, often venal, but occasionally noble forces and tendencies at work in the world at large.

That's the first point made by the U.N.'s resident therapist, Brian Urquhart, who toils in the 38th-floor office of the undersecretary general for special political affairs. Urquhart is an unflappable former British infantryman who has never forgotten his six years as a combat soldier and so has never lost faith (nor acquired any illusions) in the course of a 37-year career that now finds him in charge of U.N. peacekeeping missions.

Urquhart has nothing good to say about the Arab campaign to suspend Israel's right to participate in the U.N. General Assembly -- except that it would certainly collapse, as indeed it has. A triumph for the Reagan administration's tough talk? Partly, but also a vindication of Urquhart's faith that every so often sanity prevails.

Even before administration honchos went public, Urquhart was predicting that the anti- Israel campaign would fall short. The chill-factor of a possible U.S. walkout was evident, without the explicit threat. Cooler heads (Pakistan, Senegal, Malaysia, Bangladesh) in the Islamic bloc were counseling restraint.

At a 40-nation Islamic caucus, Pakistani Foreign Minister Yaqub Khan had already made the case: that Israel's ouster would reinforce American public support for Israel at a time when it was severely shaken, while the effect on the Arabs' standig would be just the opposite; that without U.S. funds, the U.N. would be hard put to care for Palestinian refugees; that Israel would be free to ignore U.N. peacekeepers on the Golan Heights, where they contribute more to Syria's security than to Israel's.

Most Arabs know all this, Urquhart insists. Yet they feel compelled to shout no less loudly than the ringleaders, Libya and Iran. Why? "It's a sort of group psychosis," Urquhart explains. "The most extreme voice tends to sway everybody, even if nobody agrees." That's not unique to U.N. life.

Yet reason can prevail, Urquhart argues. And it prevails in its own wacky way precisely because, on balance, the United Nations is at least as susceptible to good uses as it is to abuses. What makes this often difficult to recognize is that the organization's good uses, in Urquhart's words, "have to do with things that don't happen."

For example: if the Soviets actually move troops into Poland, Urquhart reckons that -- "with all the brave words" -- it would be a repetition of Hungary, 1956. The United States would have the unacceptable option of a nuclear showdown with the Soviet Union.

So it would opt for the United Nations, and the Soviet veto in the Security Council would transfer the problem to the General Assembly. A huge majority would tell the secretary general to do something. The United States and anybody else concerned could then blame the secretary general for doing nothing.

So superpower face-saving is one useful function. Another is the role of keeping hopeless situations from getting worse. Item: Cyprus, where U.N. forces man a buffer strip between the Turkish and Greek Cypriots. "Cyprus is absolutely impossible," Urquhart says. "But keeping both sides from fighting is better than nothing."

None of this is to suggest that if you were starting from scratch today, you might not try to design quite a different world organization. More likely, you would find it impossible to create one at all. This might delight some of the U.N.'s most dedicated detractors.

But a world without the United Nations would be the same world, with the same conflicts and controversies that now find their expression in an organization over which the United States and a relatively few close friends once ruled supreme in earlier, easier times.