James Galway, the internationally acclaimed flutist, who first played with a street band in his native Belfast, recently took the stage for an encore at the opening concert of this year's 21st Belfast Festival.
Earlier, he had played his famous golden flute in concertos by Mozart and Stamitz. This time he produced two tin whistles and played a lively jig, ''The Irish Washerwoman.''
The capacity audience began to tap its feet enthusiastically to the catchy rhythm. After an evening of superb musicmaking, it was a typically Irish way to celebrate the birthday of the festival.
Eighteen days of festivities, ending Nov. 26, make this gala (apart from the Edinburgh Festival) the largest festival in Britain. The visitors this year include the State Orchestra of the Soviet Union, the National Theatre from London, and the Royal Shakespeare Company. Up to 100,000 tickets are offered for events as diverse as classical concerts, jazz, drama, opera, films, poetry readings, and even an architectural tour of Belfast, entitled ''A Victorian Walkabout.''
There have also been record-high bookings. And predictably, the major concerts featuring James Galway and the USSR orchestra, the National Theatre's ''Hiawatha,'' and the Royal Shakespeare's ''Romeo and Juliet'' and ''A Midsummer Night's Dream'' were sold out weeks in advance.
But the festival organizers have also been overwhelmed by the response to other events. For example, the Ulster poet Seamus Heaney gave a reading to a 1, 200-member capacity audience in Whitla Hall, the main campus building of Queen's University. ''We hoped to get maybe 500 people,'' one of the organizers said, ''but we had a sell-out.''
The enthusiasm is infectious as the fes
tival comes of age. It began in the 1960s, when Belfast was peaceful. ''I always looked on November as a dreary month,'' said Michael Emmerson, a festival organizer at that time. ''We conceived the festival as a means of bringing the world to Belfast and of cheering ourselves up.'' The early festivals featured little more than theater, cinema, and a pop concert. But in 1967 things began to mushroom.
The 1969 program was outstanding. It included Igor Oistrakh, Buddy Rich, Julian Bream, Memphis Slim, and many others. The director was Mr. Emmerson, then only 30. Now manager for James Galway, Emmerson returned to his old university with his star to share in the celebrations.
''This really is like the birthday of an offspring,'' Emmerson said. ''Like everyone growing up, it has had its problems. But it is now a mature and stable event. I always believed in presenting programs that I would enjoy. I figured that if I could enjoy them, so would thousands of others.''
The 1969 festival was the highlight of Emmerson's career as director. He recalls a crisis of direction and difficulties with finances. He wanted to expand by taking the festival outside the control of Queen's University. But the university authorities prevailed and, significantly, the full title today is the ''21st Belfast Festival at Queen's.''
The man who emerged from years of difficulty to guide the festival to its present maturity is Michael Barnes, an Oxford graduate and former history lecturer. A gentle, sensitive, yet outgoing man, he was once described by a reviewer who watched his performance in a play as ''resembling an El Greco saint fallen from grace.''
Over the years, Mr. Barnes and his staff have assembled a formidable array of talent, including the Halle Orchestra, Yehudi Menuhin, the Abbey Theatre from Dublin, the Royal Winnipeg Ballet, the Philadelphia String Quartet, Dizzy Gillespie, and this year's glittering cast.
The Belfast Festival has had to live with the Ulster troubles for the past 15 years. Yet the violence has not deterred international artists from coming, nor has it kept local audiences away. Barnes says that ''the big names are used to touring the world, including the trouble spots. The main reason we cannot get certain people today is because they cost too much or because they are booked up. It is not specifically because of the troubles.''
One of the best advertisements is by word of mouth. People who have been to Belfast are willing and able to share their experiences with other professionals who might be anxious about coming. Barnes says emphatically, ''It is my experience that no artist who has been to the festival is other than willing to be invited back.''
Mr. Emmerson put the point another way: ''Artists have a good time, audiences are warm and appreciative, and festival staff look after them. You can hardly keep some artists away.''
Financially, the festival is stable, but it lives literally from year to year. Its annual budget is (STR)250,000 ($375,000) - compared with the (STR)1.9 million ($2.85 million) for the Edinburgh Festival. Box office receipts in Belfast pay for 50 percent of overall costs. The rest comes from private donors (15 percent) and from the university and the government-sponsored Arts Council.