Enough already.

First, U.S. Ambassador Charles M. Lichenstein tells them they can "sail into the sunset," as far as the United States is concerned. ("Never mind that the sun sets over New Jersey," sniffed the Daily News).

Then President Reagan offers six months in Moscow. Then the Senate slashes $500 million out of their budget.

Now this: Mayor Edward I. Koch said today that he really wants the United Nations and its delegates to remain here "because every country needs a cesspool."

"I've said this a million times," Koch told a United Jewish Appeal breakfast. "The U.N. is a cesspool. It is a monument to hypocrisy. I've said that many many times, and I also say they should stay here in the city of New York because every country needs a cesspool."

Koch's audience laughed appreciatively, as the mayor added, "I enjoy having them here. It is theater. It's sometimes absurd, but always interesting."

The United Nations has an image problem. Its delegates, a cacophonous group of diplomats from 158 nations, spend their waking hours waging war over peace. It's a war they never win, and the frustration in the great glass box by the East River spills over in never-ceasing waves of bickering.

Nonetheless, the delegates think they deserve some appreciation for trying, and the events of the past week have more than ruffled diplomatic egos.

"Governments have insoluble problems," said Brian Urquhart, the United Nations' undersecretary general for political affairs. "So they dump them on the U.N. and then blame us for not solving them. No one can do anything about the Soviets in Afghanistan, so the problem gets dumped here. Everyone blasts the U.N., but where do they go when a Korean airliner gets shot down? The world is in danger and you bloody well better have one place where everybody is free to talk to everybody else."

Part of the United Nations' unpopularity here may stem from the change in voting patterns in recent years. After three decades of western supremacy, the admission of dozens of newly independent nations tipped the scales against American positions in the General Assembly.

"The U.S. has lost control of the U.N.," said Richard A. Woolcott, Australia's U.N. ambassador. "The U.N. used to be a comfortable club of allied victors in the 1950s and the U.S. could manipulate it. Now, however small a country is, it has a voice on the international stage." In a recent Roper survey, 51 percent of Americans polled said the United States should withhold money from the United Nations when it disagrees with basic decisions.

A press aide for Lichenstein said today that she had been overwhelmed with letters and calls of support since his statement. The day after, 350 supportive calls and 14 critical calls came into the office, she said.

New York politicians complain that U.N. diplomats, with legal immunity, ignore parking tickets and lawsuits. Many in the Jewish community criticize what they consider the pro-Arab bias of the organization.

Despite the dissatisfaction, however, no one seriously thinks the United Nations will move. The 35,000 diplomats and their dependents make New York an international capital, bringing $700 million into the local economy. The costs of moving such an operation would be huge. Besides, the diplomats like New York, according to U.N. officials. Some have even learned to talk back, New York-style.

"Mayor Koch is a very vulgar man," said Urquhart, a normally polite Briton, when told of the mayor's comments.

Nonetheless, the diplomats concede, there is more than a little theater in the United Nations. "Like all deliberative bodies, every once in a while it goes ape," Urquhart said. "But there's Marx Brothers activity in Congress, too, and everybody puts up with it."

Woolcott agrees. "It's easy to call the U.N. a Kafkaesque body in a glass house, divorced from reality. There's a lot of rhetoric and not a lot of identifiable action. But it does occasionally contain crises, and the machinery is still there to help keep the peace."