When the Stratford Festival originally announced the outline of its music, Victor di Bello looked hurt when he was accused of abandoning opera which had proved in the past an artistic distinction, if not always a box-office success. There would, after all, be a new opera based on Petronius's The Satyricon, with music by Stanley Silverman, the festival's music consultant and composer-in-residence.

In its realization, Satyricon abandoned its lofty pretensions and became a musical and di Bello was left with only a concert version of Mozart's The Abduction from the Seraglio to support his contention that the festival had not totally eliminated opera.

The choice did not seem an especially logical one. If opera lovers had been asked to suggest an opera for concert performance, it is likely that Abduction - a lively stage comedy - would have been far down the list. Even so, the presentation next Sunday is not without its attractions.

Mozart fans are likely to feel it is worth the price of admission just to have a chance to hear tenor Leopold Simoneau - still one of the great lyric Mozart singers - in the role of Belmonte. The generally strong cast will include Clarice Carson, Constanze; Colette Boky, Blonde; John Macurdy, Osmin; and Bernard Fitch, Pedrillo; with Powys Thomas as narrator and George Schick conducting the Festival Orchestra.

As far as the rest of the music season is concerned, public reaction has varied from expressions of horror to high praise, suggesting this is the greatest music season ever. Not surprisingly, neither seems to be fully justified.

Anyone who feels a summer festival should specialize in what is not available to the potential public during the winter musical season may justifiably be put out. Bach, Haydn, Schubert, Beethoven, Mozart and Brahms do not sound like festival fare when they are performed by concert artists recently heard in Toronto - the source of much of the potential audience.

On the other hand, fans who have been waiting for Stratford to become aware of the pop music field do have something to cheer about. Whether these additions will improve the artistic standards of the festival remains to be seen, but the available evidence suggests they may do much to bolster the box office.

Sold out houses at the Festival Theatre are not unknown for the Sunday afternoon series, but one guess should be enough to explain why tomorrow's opening program was sold out in advance. The concert is titled Bach/Rock and will feature the Procol Harum - one of Britain's leading rock groups - with the Stratford Festival Orchestra, together and separately.

Neither is it hard to explain why tickets are already in short supply for the first three concerts in the Special Events Series at the Avon Theatre. The performers, all folk singers, will be Joni Mitchell, July 10; Ian and Sylvia, July 11; and Gordon Lightfoot, July 17.

The pop attractions are not the only ones creating box office excitement. It seems unlikely there will be any empty seats in the Festival Theatre when soprano Elisabeth Schwarzkopf, one of the greatest lieder singers of our time, appears in recital on Aug. 17, or when David Nadien, concertmaster of the New York Philharmonic, performs the Mendelssohn Violin Concerto with the National Youth Orchestra, conducted by Victor Feldbrill, Aug. 3.

Although Indian sitarist Ravi Shankar will be appearing this month in both lecture and recital in Toronto, the 800-seat capacity of the MacMillan Theatre is not expected to rob the festival of its audience for his Saturday morning and Sunday afternoon lecture-recital on Aug. 23 and 24. Guitarist Julian Bream can probably count on his customary following for his lute and guitar recital, Aug. 10.

Saturday mornings, not the ideal time for most concert-goers, are also attracting special attention, for this part of Canada is generally starved for chamber music. Needless to say, the advance sensations are the imports, including the Guarneri String Quartet, this morning; the Beaux-Arts Quartet, with pianist Nina Lugovoy, July 12; and the Orford String Quartet, with clarinetist Stanley McCartney, Aug. 9.

The other events in the Saturday series, featuring members of the Stratford Festival Orchestra and first performances of commissioned Canadian compositions will take place July 19 - John Hawkins' Remembrances, for piano, harp, trumpet, horn, trombone and electronic tape; July 26 - Brian Cherney's Mobile IV for voice and nine instruments; Aug. 2 - Gilles Tremblay's Oeuvre for 11 instruments. Each program will include a work from the classical repertoire.

One Sunday program, July 20, will also fall into the chamber-music category. It will include music by Haydn, Schubert and Beethoven, performed by Eugene Istomin, piano, and Leonard Rose, cello, assisted by Nadien and Arthur Garami, violins; David Mankovitz, viola; and Malcolm Tait, cello.