There was something thrilling about watching our finest composer, Aaron Copland--the artist once banished from official Washington--conducting the National Symphony on the West Lawn of the Capitol last night. There are times when this country chooses to praise its famous men, like the 81-year old Copland, while they are still ours.

Just after 8, Copland walked onto the makeshift stage facing the Capitol building from the foot of the West Lawn. The man whose music was banned from President Eisenhower's first inauguration because its composer was said to be "subversive" was greeted with a standing ovation from an audience estimated at 35,000 to 40,000 people. Then he conducted the National Anthem and, with no prompting, the crowd turned to the flag on the Capitol dome. Many put their hands over their hearts. A large number of the concertgoers were too young to remember firsthand the 1952 inaugural or the McCarthy era, but many seemed to appreciate the event's emotional significance.

After the anthem, which regrettably is not a composition of Coplandesque quality, the evening was all-Copland, with much of the man's formal diversity and musical flair. There just isn't much in musical composition that the man hasn't mastered--except, in this listener's opinion, opera.

The opening work was the "Fanfare for the Common Man," that great World War II expression of the grandness of American ideals, if not always of our purposes. The "Fanfare" sounded splendid--though passing judgment on a performance in such an acoustical setting is always tricky.

Then came the exuberant "Outdoor Overture"--just the work to play the day after the concert had been postponed because of Sunday night's storms. Following the "Overture" was that glorious paean to the rawness and monumentality of the American frontier, "Billy the Kid."

But the most moving moments were elegiac. First there was the lyric, serene music Copland wrote for Thornton Wilder's "Our Town." Though it is for a large orchestra, it has all the tenderest attributes of chamber music--much less craggy than most of Copland's own chamber compositions, splendid as they are. The conducting and the orchestra's playing was moving indeed.

So were the performances of five of Copland's "Old American Songs" by the redoubtable baritone Richard Stilwell. He performed, as usual, with exemplary musicianship and diction. When he started singing "Simple Gifts," which is the climactic melody of "Appalachian Spring," the listeners broke into applause. Of course they should not have, but given the happy vibes of the event, who can blame them.

As an encore, there was the "Hoedown" from "Rodeo," to which the delighted crowd clapped in unison on the on-beat.

The National Symphony seems to have substantially solved the amplification problems of its West Lawn summer concerts. The orchestra's executive director, Henry Fogle, put his finger on the problem last night: "Because of the echo it sounded like we were having two concerts instead of one. The first came from the stage and the other one echoed off the Captitol building slightly later."

Now, with a new sound system, in which the speakers rise higher above the sides of the stage and the feedback speakers farther up the Hill have been eliminated, the sound is notably cleaner, with the echo minimized so that it's not much of a problem. Outdoor concerts at the Capitol, though, are never going to sound like Carnegie Hall.