I AM STILL a rather melancholy person, often wanting to be where I am not, for reasons I cannot explain and do not believe to be explicable," Rudolf Bing, at one time the opera world's most powerful man, wrote in his memoirs, "5,000 Nights at the Opera."

So it is with Rudolf Bing, 75, in retirement. And so it has often been. In 1972, as he neared the end of his 22-year reign as general manager of the Metropolitan Opera - which he ruled with a firm, if not autocratic, hand, once even firing Maria Callas - Bing was anxious to move on. He said that he had waited "till the last possible day to get out alive."

Then, after teaching six semesters as professor of music at Brooklyn College, he recalls, "I felt like a phonograph record." So he moved on again. His restlessness even pursues him on vacation; he recently spent three months with his wife in the Dolomites in Italy, where in his youth he would accompany his family for vacations from his native Vienna. But three months, he says, was "too long"; he prefers working.

For more than three years he's been on the board at Columbia Artists Management Inc., the colossus of classical music management in New York, doing what he's done since he was 19 years old in Austria - engaging in the business of music. Yet he says, laughing. "That's why I don't like it. I had enough of singers."

But the truth of it is that Rudolf Bing misses his days at the Met - misses them terribly.

"It, indeed, was an all-day, all-night job," he says. "But despite everything - the worries, the burdens, the sorrows, the excitement - I enjoyed every moment. It think people should work as long as they can if they have their health. Of course, this is all hindsight. I couldn't do it now. I'm an old man."

Sir Rudolf - he was knighted by Queen Elizabeth in a 1971 Buckingham Palace ceremony that he admits was "a thrill" - is still quite active. Earlier this year he put together a concert of young American singers at Town Hall in New York. And he's currently organizing eight appearances by world-famous prima donnas, scheduled for Carnegie Hall beginning in November.

"It's a hell of a job," he says. "I am not saying I am working 14 hours a day. I come in every day, but I don't stay running eight hours. I am not clock watching."

He spends his evenings in his Central Park South apartment reading - "the classics, anything good" - and socializes little. "People in New York don't go out at night," and, besides, he adds, "I 'm not a very social person. I heardly see anybody." He says he's been back to the Met only two or three times in the five years he's been gone.

What figured heavily in his retirement were often-recurring artist-management conflicts that wearied him, he says. He didn't want to face yet another contract wrangle after a rather stormy decade in the '60s: Secretary of Labor Arthur Goldberg had to smooth out a 1961 crisis; five years later an orchestra strike threatened the opening of the new house in Lincoln Center; and finally, a 1969 deadlock delayed the opening of the season for three months.

Looking back, he wishes he had stood and fought a while longer, mainly to overcome the Met's bleak financial picture. That situation has grown so bleak in the '70s that a Met official said in 1975 that the Met would be out of business by July 1976, except that "we do not intend to permit" it. Bing says wistfully, "I have some inane optimism that the Met won't go under."

What sort of leader could get it through?

"A combination of Churchill and Chagall," he says. "I am not saying I was that, but anyway I tried."