When Barry Tuckwell was 13, he started playing the French horn. When he was 14, he was offered his first professional symphony orchestra position. Today he is the world's most recorded horn player, and one of its busiest.

From his London home, the 48-year-old Australian-born musician travels around the world with his horn. "On an airplane," he said not long ago, "it goes underneath the seat in front of me. I have to take out some of the slides to make it thinner. At the security check it photographs very well. And an amazing number of people know what it is. 'That's a French horn,' they say."

Whether the elegan-looking instrument, made of some 20 feet of brass and copper, should be called a "French horn" or simply "horn" is problematic, Tuckwell said. "One year the International Horn Society passed a resolution and said it should be called 'horn!' I was president then so I was not in a position to argue. Now I am not the president, I call it the French horn. But I think this is a foolish point."

Tuckwell, who performs tomorrow night at Wolf Trap, gives the appearance of ease while doing things many colleagues find fiendishly difficult. "I keep seeing it said that the horn is the most difficult instrument. Perhaps that's because it goes wrong quite quickly and that's very noticeable." With a wry smile he reveals "the pieces that used to frighten the daylights out of me: Bruckner's Fourth Symphony and the 'Oberon' Overture.

"In a way, the Bruckner is a greater responsibility because the piece is long. If the beginning goes wrong or if it isn't played with the correct magic it's much better to stop for five minutes and say, 'Look, we're going to have a smoke and then we're going to start over again in five minutes time.'

"It's easier to start a piece like that confidently , but it you do, then it's not magic."

Tuckwell has quite a name, among both his colleagues and his fans, for performing what often seems like magic. But he analyzes very clearly how he prepares for any performance.

At a recent National Symphony appearance he played two concertos on one program. "During the orchestral introduction to the Hydn," he said, "I was playing the instrument to make quite sure I was in tune. Backstage I did very little warmup. I had to pace myself. I reckoned that I had to be very careful not to think, 'Oh how wonderful!' and practice all these wonderful things in the bandroom before going on, and then find out that I didn't have the stamina to get to the end.

"This sort of pacing is to me one of the essential parts of playing. So I did a little bit to find out where I was - what state was the embouchure? This is what makes every performance different.

"I like to divide myself into two halves mentally: One is the artistic, saying, 'I want this phrase to go like this.' The other side is the engineer who says, 'Well look. We haven't got enough fuel to do that, and so if you want to get to that, you have to fly at another altitude.'

"It's always a compromise. It's better to do it that way than to say, 'I'm going to play it this way, come what may. You wreck something and everybody's disappointed.You've spoiled a piece of music. On the other hand, I don't believe in playing to safety."

How does this master horn player assure the brilliance of his playing while avoiding playing it safe? As Tuckwell teaches young players in his frequent master classes, "There has to be some preparation, even to strike a key on the piano, 'even if it's ever so slight. Obviously with an instrument like the horn, it requires a greater physical effort I've tried to minimize the waste of energy that takes place at this point. Many players tense, and their whole bodies tense. They take a breath, then they hold it. Then they get their embouchure set, then they put the mouthpiece there." He paused for a moment while a look of symphathetic commiseration crossed his face.

"Then what happens? They're so tense that the chances of getting the right note at the right time with the correct dynamic are minimized. My whole approach is to try and make the actual production of the sound as near to being natural, like speaking, as possible."

It all sounds so simple.

But the musical world that keeps him occupied non-stop is a wide one: "The repertoire is larger for horn and orcestra: Strauss, Mozart, Haydn, Hindemith, Weber, Telemann."

Tuckwell calmy added that he is now in the midst of preparing 11 record programs for the BBC World Service. "Thirty minutes each. And I've got to write the scripts for them!" - as if the world's busiest horn player did not have enough to do. CAPTION: Picture, Barry Tuckwell; by James A. Parcell - The Washington Post