No longer do his strolls through the corridors of the United Nations draw packs of reporters hoping for an audacious quote. Instead, he has faded out of the headlines in away that has caused puzzled diplomacy watchers to ask: "Whatever became of Andrew Young?"

That is quite a change from the time, a little more than a year ago, when much of the discussion about the then-fledgling Carter administration's foreign policy centered on what was known as "the Andy Young problem."

Among the various groups that brush against Young in his role as U.S. ambassador to the United Nations there is considerable disagreement about what this change means.

Some have interpreted his slipping into the background as a fall from grace - that he has been muzzled and that seemingly subtle shifts in U.S. policy toward southern Africa are a sign of diminished influence.

Yet among those with a better view of diplomacy's inner workings - his fellow U.N. ambassadors and the backstage officials who turns the wheels at the State Department and the White House - it's hard to find anyone who agrees that such epitaths are justified. They say Andy Young still casts a long shadow over the policy decisions of the U.S. government and the affairs of the United Nations.

The difference between then and now, they say, has been a little-noticed evolution in Young's approach to his job. What emerges from talks with diplomats. U.S. officials and Young himself is a portrait of a man who has changed not his beliefs but his tactics, who has subjugated many of his outsider's instincts to working within the system and who now seeks to make his point in behind-the-scenes negotiation rather than on the front pages.

"Andy has learned a great deal about the mechanics of diplomacy and how to make it work for him," says the U.N. ambassador of a major Western European nation. "He now knows all about instructions and cables and channels - about bureaucracies and who pulls the strings in them. In the process, he's become less colorful, but, in my opinion, much more effective."

If so, that is quite a difference from the image Young projected when he first moved into the U.S. mission here. Then, he seemed unique - a veteran of the civil rights movements personifying all the churning currents of 1960s dissent who smashed the icons of traditional diplomacy in ways that earned him such sobriquets as "the loose cannon" and "the wayward missile."

Young preferred other military terminology to describe his role. He viewed himself as President Carter's diplomatic "point man" - the person out front who drew hostile fire by enunciating controversile positions, but who also served as the catalyst in bringing these positions forward so they could become subjects of public discussion.

It was a mission be undertook with gusto, igniting a chain of controversies with his outspokeness on subjects ranging from Cuba's stabilizing role in Angola to normalization of U.S. relations with Vietnam to the racism allegedly lurking in the hearts of various former presidents.

Inevitably, his comments led to endless discussion about whether Young, the activist disciple of the Rev. Martin Luther King Jr., was a truer representative of Carter's thinking in foreign policy than ostensibly more authoratative figures such as Secretary of State Cyrus R. Vance and national security adviser Zbigniew Brzezinski.

In retrospect, most informed observers agree that such theories were an oversimplification fostered to some extent by the tendency of press and public to look at complex issues in terms of personalities.

Young unquestionalby had a commanding voice, but people who have observed him insist he was never more than one of several influential forces. Given the emphasis on collegiality, they add, it was inevitable that Young would come under pressure to curb his rugged individualism and find niche in the pecking order.

Most U.N. observers date this change from the events that began to overtake Young last summer. First, he called down a firestrom of criticism on himself when in the course of commenting on the jailing of Soviet dissident Anatoly Scharansky, he said that the United States had its own "political prisoners."

Then, what had been regarded as the biggest triumph for the Young approach to southern Africa - a plan for U.N. supervision of Namibia's independence from south Africa - threatened to come unglued when Pretoria announced it was pulling out of the deal and holding its own majority rule elections in Namibia.

That caused Vance and a group of western foreign ministers to rush to South Africa and patch together a torturously ambiguous compromise. Although no one seems certain of where it will lead, the west contends the aim was to allow South Africa the face-saving device of separate elections in exchange for U.N.-supervised elections that would supersede them at a later date.

However, western explanations and pleas for patience have been met with intense suspicion in black African countries. In their view, the Pretoria compromise looked very much like a cave-in to South Africa and a swing toward the pre-Carter administration days when Washington took a cautious and conciliatory line toward the white minority governments of southern Africa.

All that has prompted speculation that Young has lost control of Africa policy to administration hardliners.

From his 11th-story office in the U.S. mission here Young looks out imperturbably on the fray. Where other U.N. officials talk of the Namibia dispute as if it were a time bomb with a defective fuse, he says with unequivocal self-confidence:

"There will be a U.N. presence in Namibia by Jan. 15. It (the original U.S.-fostered plan for U.N. supervision of independence) will be tremendounsly successful."

And, on larger question of whether he has been silenced and stripped of power. Young replies: "There hasn't been any time I've been overruled. I've been clarified, and I've been qualified, but I don't think I've been compromised."

"When I first came here," he explains, "I identified the big problem as one of establishing U.S. credibility in a world where the United States is in a minority. Our South African involvement had alienated us from the Africans, the Panama Canal isue had alienated us from the Latin Americans, and Vietnam had alienated us from almost everybody.

"I tried to establish that credibility in several ways. One was to put my main emphasis on southern Africa, the last bastion of racist colonialism. I wanted to show, on behalf of the Carter administration, that the United States could play a big role in the U.N.'s decolonization work - that we have moral power to lead the world rather than just the military power to dominate it."

"Also in that first year," he adds, "It was necessary for me to say things in as honest and forthright a way as possible to endure my credibility. I wanted the Africans and other Third World people to know I was aware of things that don't always get discussed in the West. That shocked some people in this country, but I think it also educated them to the way some things really are."

Now, Young argues, the credibility problem has been solved through the administration's policy initiative in Africa, the Middle East and elsewhere. As a result, he contends, there is less need for him to play the "point man" role, and he has shifted his intention to other problems.

"The second responsibility I accepted when I came here was the task of trying to make the U.N. system work - of being able to get the votes that will determine the U.N.'s direction. It's not the kind of thing that gets you in the newspapers, but that's the job I'm trying to learn how to do now."

He adds, "I think it's important because I see the United Nations as a means of avoiding violence by putting problems into a political process that drains their potential for violence. If you can do that, there's no way you can lose - even if you're on the losing side of a vote. Because what you've done is give frustration an outlet, without which it could well up into violence."

Some sources here give mixed reviews to Young's efforts to break away from his identification with Africa. Diplomats from Latin America where Young is loved almost as much as in Africa, complain that his eyes glaze over whenever they try to interest him in their regional problems. The ambassador of an important Arab country says he recently sat through a dinner beside Young without a single word being exchanged on the Middle East situation.

However, others who know him well say that when he avoids subjects like the Middle East, it is because of deliberate policy designs. Among most of his colleagues, they add, he commands wide respect for having mastered the intricacies of a wide range of global problems.

In particular, many point to his increasing interest in the North-South dialogue - the search for more equitable trade, development and wealth distribution between the industrialized and underdeveloped nations.

"There's still a big gulf between the United States and the Third World on these subjects," said a European ambassador. "But, more than anyone else, Andy has been responsible for turning around some of Washington's traditional conservative attitudes and getting some serious attention for the dialogue."

"If you're looking for a measure of his influence in the U.S. government, I think this is the area to watch," the source predicts.

For the moment, though, most observers trying to calibrate Young's standing within the administration have their attention fixed on the Namibia situation. They are watching to see whether South Africa will come back into line and, if it does not, what the United States will do about black Africa's demand for severe economic sanctions against Pretoria.

It's no secret that the United States and Western Europe, with a heavy dependence on South African mineral exports, cannot afford to go along with these demands. But when South African Foreign Minister Pik Botha comes to the United Nations this week, he will be on notice that Washington is weighing the idea of selective sanctions such as the halting of commercial air traffic to and from South Africa.

No one in the U.S. government has threatened such sanctions publicly, but everyone at the United Nations is aware that the rumors of these possible measures are being orchestrated from Young's office. To many here, this is a sign of how skilful Young has become at playing diplomatic hardball.

As for Young, he replies to questions about sanctions by smiling like the Cheshire cat and repeating his confidence that "things will work out fine" one Namibia.

"I don't think my credibility is on the line," he says. "What protects my credibility with the Africans is not my ability to deliver. It's being honest with them."

Asked what he will do if things do not turn out according to his expectations, Young replies: "As long as I'm confident U.S. policy is moving in the right direction, I don't expect to win every battle."

"It's like football," he concludes. "You get two yards here, three there, and now and then you're thrown for a loss. But when you are, you don't walk off the field and quit. You pick up the ball and try to work another play."