Kurt Masur is just two and a half years away from his 80th birthday. But his work schedule would tax many a conductor half his age.

He's giving nine concerts this month in five countries, including a complete Beethoven symphony cycle in Athens. Next month it's 12 concerts on two continents. In the early 1990s he was conductor of both the New York Philharmonic and the Leipzig Gewandhaus orchestras. Today there are still two, but now they're both on the same continent, the London Philharmonic and the Orchestre National de France. In conversation, he reveals his age mostly through references to the educational projects he's involved in, and his desire to pass on the benefit of his long experience.

He says he has discovered a major conducting talent, born on a small island in Greece, who's steadfastly refusing to make all the obvious career moves. He won't divulge the name of the 25-year-old woman, but she is, he says, "so highly musical and talented that I must say this is one of the upcoming great conductors, I'm quite sure".

Masur has never had much affection for the glamour of the musical world. He can't have experienced much of it when he launched his career in the German Democratic Republic in 1948. He was born in Brieg in Silesia (now Brzeg in Poland), and received his musical education in Breslau (now Wroclaw) and Leipzig. Things were very different for young conductors in the post-war years, he says, especially in Germany. "There were a lot of conductors missing, the older ones, and we had a great chance to start immediately. I started in the Theater of Halle, the city of George Frideric Handel, and after half a year they already asked me to conduct operas." He was just 21.

Standards may not have been the highest, but, "people needed a build-up of their spiritual life". Today, he says, there's an abundance of well-educated conductors whose growth potential is limited because they can't acquire the necessary experience. When Masur was young, it was still a time in Germany "when a conductor was a person who was respected from the very beginning. This doesn't exist any more. The respect is something you have to earn."

His warning to young conductors today is that "if you don't know more than the orchestra knows, they will not respect you". The technical standards of orchestral players have risen enormously in the half-century and more of Masur's career. The kind of orchestral discipline that was once the preserve of only a handful is now quite freely available, at least in the familiar works of the standard repertoire. The levelling effect makes it all the more important, says Masur, for the conductor to be an inspiring presence.

"If you let them play, they can play without you. I tell this to every young conductor, and I've proved it, in master classes. One young man was beating all the time so clearly that they played mezzo forte all the time. If he wanted to have a pianissimo he didn't achieve it, because he was thinking too much of keeping them all together. I told him, 'Just give the upbeat now, and let them play.' He was astonished at how long they could play together, and he was even more astonished that they played a better pianissimo than with him. We really should know first the meaning that we want to achieve from the orchestra. Music must speak to the audience."

The centre of power has also shifted in a way that Masur sees as a threat to musical values. Conductors are weaker, and managers have become stronger. He talks with evident distaste for what he calls marketed orchestras.

"In my time with the Gewandhaus Orchestra, I still was the ruling person. It came from the time of Mendelssohn [the composer was a key figure in the development of the Leipzig orchestra]. I was responsible for everything - though with the right people around me, of course, with knowledge of finance and so on. More and more, it fades out. Marketing has become the first thing.

"It leads to very strange ideas. I offered in San Francisco to do a cycle of all nine Beethoven symphonies. And then the marketing director asked me, 'Please start with No. 6 and No. 7, then we sell better.' I said, 'then you will have to conduct. Because I would like to give the people the feeling of how Beethoven grew into the musical language of the Ninth Symphony from the beginning of the First.' Otherwise the cycle doesn't make sense. It only makes sense if the people can take part in the growth in the composer's ideas."

There has been a lot of worry expressed about the decline in the record industry. But Masur sees some of the changes wrought by technology as positive. "The stars were created by the record companies. Now we have a little more natural feeling again, because everybody can advertise himself. This is for me, now, a new beginning, a time where you can be interested in people you wouldn't normally discover."

He encountered the work of the young Greek conductor on video, and, clearly impressed by someone who, he says, is uninterested in the star system - "she wants to grow up by herself" - he plans to introduce her to his orchestras in London and Paris.

He singles out Simon Rattle for praise. "He was in Birmingham a long time. He could have become known much quicker. But he waited until he felt safe."

In spite of Rattle's involvement with performances on period instruments (about which Masur says, "the contemporary instruments do not give you the guarantee that you are right about the spirit of the piece"), he's convinced that Rattle is very aware of tradition. "Otherwise," he laughs, "he wouldn't have the idea that the Berlin Philharmonic would be a good goal."

Furtwängler was an inspiration to the young Masur, and Bruno Walter even more so. He liked Walter's ambition to make each line sing, and was impressed by his approach to the musicians, calling them "friends". Walter's famous recorded rehearsal of Mozart's Linz Symphony made a deep impression.

By contrast, he reacted against Toscanini. "It's a great danger to play mechanically, with great precision, but never taking time to speak with the music. I never could accept his Brahms interpretations. I admired his Rossini. His Otello is beautiful, and driven, which is necessary for Verdi. Italian music is in the best hands with him. It's astonishing what he could achieve, the right rhythm in the Seventh Symphony with very fast tempi. It's only because, as we know, he was able to beat musicians if they were not going his way. This time is over. Toscanini wouldn't survive now. Orchestras would say no."

Masur owns up freely to having made a lot of mistakes. "I was from the beginning a conductor who wanted to sing with the music, to let it flow, to have beautiful sound - until I discovered that there is some music which should sound aggressive. There are sometimes places in the music where you need the harshness of Toscanini, or even the rhythm, which is exciting, and not just right. Everybody has to discover his weak points in order to overcome them."

When he realised his concern with tonal beauty and singing lines was compromising his handling of rhythm, he took up the study of percussion for a number of years, and now, he says, nobody would believe how different his conducting was before he did that.

He had to be told by musician friends to be firmer with the players. "They told me, 'If you are in front of us, you sometimes must tell us how ugly we play. If you only smile, even when we play badly, it's no help to us. We expect you to be our best audience, to listen, to tell who is wrong and who is right, and what way you want to go."

And he had to overcome a shyness so extreme, he says, that when he was in his teens, no one would have believed he could ever become a conductor. In fact, he only turned to conducting when his ambition to become an organist was thwarted. At 16, he lost the use of the little finger of his right hand.

For a shy man, Masur's leadership of public demonstrations for change in the dying days of Communist rule in East Germany might seem ratherstrange. "I was shy but confident. All I had to do there was do the right thing at the right time. I had influence. I was the Gewandhaus Kapellmeister. I was one of the successors of Mendelssohn. The position was strong in that city. It's only half a million people, and the orchestra had the respect of the people. I felt that I had influence, and I just used it at that time." What followed after reunification, he says, was a vacuum at the top.

"Helmut Kohl had helped to make it possible, but his leadership afterwards, for the people of the whole of Germany, was non-existent." Perfectly good East German produce - he instances butter and mineral water -was ousted by superior marketing skills, serious unemployment followed, and the seeds of mistrust were sown. Yet, he points out, Germany is still a rich country, and, he says, Germans complain too much.

It's a response which alienates him. He is, he says, a fighter by nature. "The London Philharmonic has problems, but we fight together as well as we can."

He compares the unfavourable situation in London now with the "blooming" scene when he first conducted there in 1967. In Asia, he says, "there is a great army of music lovers and of musicians, hungry for the music of the European tradition. You don't find orchestras anywhere any more without players from Asia. So, watch out!"

Some things, however, remain stable. Beethoven, whose Sixth and Seventh Symphonies he conducts in Dublin, "never lost his influence. I think even if people have no knowledge about his life, they feel that this man has built up his music so deeply, that this musical language touches your heart but makes you also active. He never ends a symphony with a kind of resignation, like Tchaikovsky in his Pathétique, which is a farewell to the world."

It's not just on the concert platform that Masur is active in Beethoven's cause. He's the chairman of the board of the Beethoven House in Bonn, he's involved in furthering a new, scholarly edition of the symphonies, and he's hoping to provide a final resolution to the disputes about the composer's controversially fast metronome markings.

He's also involved in fund-raising gala concerts for the International Mendelssohn Foundation established in 1991. He has done one in Paris, and hopes to follow this with galas in London, New York, Tokyo and then Germany. The idea is to make people aware that Mendelssohn was "as great a composer as the other ones".

And stranded through everything runs the contact with the young, the desire "to pass on my knowledge of the tradition, so this doesn't get lost". While Masur remains on his feet, there seems to be little risk of that.

Kurt Masur conducts the London Philharmonic Orchestra in Beethoven's Sixth and Seventh Symphonies in the NCH International Orchestral Series tomorrow