Aaron Copland returned to the Federal Enclave yesterday with a certain glow of octogenarian glory.

Copland, 81, is here to conduct the National Symphony in a concert of some of his most famous works. The event, which was to take place on the West Lawn of the Capitol last night, was rained out and has been rescheduled for tonight. The Park Service waited until the last possible moment to cancel the concert, but fortunately the bad weather hit early enough to prevent large numbers of music-lovers from being drenched.

The Capitol symphony concerts are mass experiences attended by tens of thousands. These events, so much the product of the second half of the century, are hardly the kind of thing on which Copland's teacher, Nadia Boulanger, nurtured America's most eminent composer during his formative days in Paris.

"But that's how times change," he observed wryly in an interview yesterday. "You know, it was wonderful being 20 during the '20s, particularly in Paris, but that means I have to be 80 in the '80s." Only his own word would convince you of that, he looks so youthful and fit. Perhaps his main concession to his years is that he seems slightly hard of hearing.

Another example of how times change is the fact that 30 years ago he was persona non grata in the Federal Enclave. His "A Lincoln Portrait" had been scheduled for the first Eisenhower inaugural concert and then was banned. Rep. Fred E. Busbey (R.-Ill.) had insisted that Copland would never do because of his association during his youth with "Communist front groups."

"The inaugural concert of President-elect Eisenhower is no place for Copland's music," the congressman declared at the time. "There are many patriotic composers available without the long record of questionable affiliations of Copland."

Given what he went through at the time, Copland's equanimity on the subject is startling.

"You just have to wait for history to take its course," he said yesterday. "Things like that die out very gradually. And if you live long enough--and I certainly can't complain in that respect--and if you are persistent. You know, one has to be persistent to get anywhere in this life."

Copland is droll on the subject of his physical health: "It must be because of all this conducting and exercise that I've been getting in the last 30 years. I hope it isn't disrespectful of me to say that I couldn't really start conducting until after Serge Koussevitzky the longtime conductor of the Boston Symphony and e'minence grise of many modern composers died in the early '50s. He just wouldn't have permitted it. You know, at times he almost ran my life. When I mentioned conducting he ordered me back home and said, 'You keep writing. You should stay home and compose. Don't waste time conducting.' I think he was right.

"But conducting is fun. Obviously I don't stand up there and conduct with the authority of the greatest conductors, but I certainly know my own music well.

"You know, I think that Koussevitzky was a kind of repressed composer himself. He would have loved to be a composer. It was Nadia Boulanger who got me to know him in Paris and then one day she told me that he had just been named the conductor of the Boston Symphony. That was back in 1924. And it was one of the best things that ever happened for me, though I didn't realize it at the time. After all, you have to have some luck in this world."

Asked if he was bitter about the way conservative politicans stigmatized him in the '50s, he replied, "Oh no, that was so long ago. I took it as one of the facts of life. And things in life have gone so well for me. And I feel really gratified about this concert at the Capitol.

"And anyway, if you write music with harmonies and rhythms that some people may not like, and that was always the way, you have to expect not to be liked. Even by the critics. But you know the ultimate fate of a piece of music does not depend on whether either the politicians or The New York Times likes it."

"And one has to really believe in the music that you write."

Then Aaron Copland takes you by surprise by raising, with no prompting, the question of how his musical legacy will be remembered, and he says, "I just don't know. It could be anything. There is no way that any composer can know the fate of a piece of music when he writes it. You just can't worry about that." His principal undertaking now is an autobiography that will also serve as a firsthand history of music since the 1920s.

One thing that he was not prepared for when he wrote much of his music was its enormous popularity.

"Would it have affected you," he is asked, "if you had realized that 'Fanfare for the Common Man,' for instance, would have been known by 40 or 50 million as a CBS logo?"

"Well, no," he answered, "but I do think that the inspired title may have helped."

Then he added with a pixieish grin: "I thought of it myself."