With the ending of last week's U.N. debate on Palestinian rights, Andrew Young has taken his last bow in the ambassadorial role that made him one of the few larger-than-life personalities of the Carter administration.

He leaves in the same way he came 2 1/2 years ago, amid a blaze of controversy. In this instance, it was ignited by disclosure of his secret meeting with a representative of the Palestine Liberation Organization and his subsequent public rebellion against administration Mideast policy and his intimations of State Department spying on his activities.

Inevitably, Young's myriad critics have taken the stormy circumstances of his departure as proof that their judgment of him was correct; that he was a product of the churning currents of 1960s dissent intent on smashing the icons of traditional diplomacy and therefore unsuited to the demands of the U.N. ambassador's job.

But, while the PLO incident does give considerable support to this argument, it also has tended to distort and obscure an understanding of the significance of what Young accomplished in the U.N. post.

He transformed what had become a glorified public relations job into an important and influential vantage for the conception and execution of U.S. foreign policy. As a result, Young's departure has left a void in the administration's policymaking machinery, and has confronted President Carter with some sensitive decisions about how to fill that void without damaging his long-range policy goals.

The assignment Young staked out as his own was that of chief U.S. interlocutor to the Third World in general and to the countries of black Africa, in particular, where American influence had reached an all-time low during the Nixon-Ford era.

In pursuing this role, he found an ideal arena in the United Nations, whose membership progressively has become dominated over the past two decades by Third World nations. To them, the United Nations is the only universal forum where they can band together to make their voices heard and try to exert influence on the industrial powers of East and West.

Over the years, the United States has shown considerable ambivalence in dealing with this phenomenon. At one extreme was the approach taken by Daniel P. Moynihan, the most prominent of the Nixon-era U.S. ambassadors.

Moynihan, now the Democratic senator from New York, chose to confront the often shrilly anti-American rhetoric of Third World delegates head on, counterattacking fiercely and provoking frequent acrimony.

It was the kind of colorful stuff that won the plaudits of those domestic nationalists who constantly wonder why the United States bothers to stay in the United Nations. But, as even Washington's staunchest allies frequently pointed out, if the United States wasn't going to quit, such tactics only had the counterproductive effect of further estranging the United States from the Third World.

Then came Young, the disciple of the Rev. Martin Luther King Jr., intent on applying the principles of the American civil rights movement to the arena of international relations. Like a diplomatic exorcist, he talked unabashedly of driving out the evil spirits that had bedeviled U.S. relations with the Third World and leaving only what he called "the essential goodness of the American people."

It was a message he expounded with all the skill and zeal acquired in his years as a preacher. More important, Young was able to demonstrate that it wasn't just rhetoric, that his personal clout with Carter was able to reverse the State Department's long neglect of Africa and bring about a new high-priority emphasis on trying to resolve the racial conflicts and injustices of southern Africa.

In the process, Young, for all his frequent lapses into the hip shooting, outrageous statements that earned him such sobriquets as "the loose cannon," became, in the near-unanimous view of veteran U.N. hands, the most effective ambassador Washington has had there in at least a decade.

That was the opinion being expressed both publicly and privately in U.N. corridors last week. And it came not just from the African and other Third World delegates, but also from the ambassadors of those European countries that originally had tended to regard Young as a man hopelessly out of his depth.

Most said that Young, after a rocky start in his first months, had learned to subjugate many of his outsider's instincts to working within the system and had become very adept at behind-the-scenes maneuvering and manipulation of the levers of power.

Even the event that ultimately brought him down -- his crashing on the shoals of the PLO incident -- privately was seen by many of his colleagues not as an attempt to frustrate or undo a U.S. policy position but as a tactical way of trying to fulfill Washington's instructions to win a postponement of the Palestinian debate.

As one European ambassador, who asked not to be identified, put it: "It was a situation that many a diplomat has faced. You're ordered to do something, and you feel the only way you can do it is go off on your own and exceed your instructions without telling your bosses.

"You can go by the book or you can gamble," he added. "Andy chose to gamble, and unfortunately he lost and had to take the consequences. That's the way the game is played. But it's a pity. I shouldn't think there's someone here who isn't sorry to see him leave."

Predictably, the greatest anguish at Young's departure was expressed by his African colleagues, whose feeling for Young was described by a European ambassador as "a relationship so intense and mystical that it was almost like a love affair between a man and a woman."

As Arab and African diplomats agreed to postpone a vote on the bitterly controversial resolution supporting Palestinian self-determination, they attributed their decision to their respect for Young.

Of the many tributes paid Young in the wake of his resignation, perhaps the one bust summing up the feeling of the Africans was Zaire Ambassador Kabeya Wa Mukeba's observation that Young "transcended the limits of the two great philosophies that dominate the world. He has a vision of the world more complete than that of other Americans."

It is a sentiment that State Department officials say President Carter will be unable to ignore when it comes to a choice of Young's successor. Despite the acrimony that arose between Young and the department in the aftermath of the PLO incident, department officials, particularly those dealing with Africa, and the Third World, insist that they regard his resignation as a serious loss.

"Although the Africans were very unhappy about it, they at least realize that Andy's resignation was forced by circumstances that had nothing to do with African matters," a senior department official said. "Now it's going to be very important to reassure them that his departure won't mean any change in our policy toward Africa.

"In fact," he added, 'if there's any comfort at all to be drawn from the whole sad affair, it's the chance to demonstrate that Andy, for all his superb skills as an advocate and articulator of our Africa policy, wasn't its sole author, that it wasn't just Andy Young's policy, but Jimmy Carter's policy and Cyrus Vance's policy as well and that it's going to continue."

That is why most speculation about Young's successor has centered on such names as Donald F. McHenry, Young's principal deputy at the United Nations, and former Democratic senator Dick Clark of Iowa.

Before he was defeated for reelection last year, Clark headed the Senate subcommittee on African affairs. McHenry, a black former Foreign Service officer, worked closely with Young on all his major Africa initiatives.

Some administration officials say privately that it might be a mistake to replace Young with another black or even with someone identified as an African expert. Such a move, they argue, could transform the U.N. ambassadorship into the diplomatic equivalent of the old "Jewish seat" on the Supreme Court and create the impression that the job is essentially restricted to dealing with African affairs.