'Opera began with the idea of inserting music into a play," says conductor David Stern, resting in a half-lit office of the Israel Opera between rehearsals. He's here to conduct the Israel Opera/Bern Opera co-production of Handel's Julius Caesar in Egypt. "The baroque opera" - of which Julius Caesar is an example - "focuses on telling a story. It is not about beautiful sounds," he says. "That is why I love doing it, because all operas should be about telling great stories. I love the voice and I love the music, but if the music doesn't serve the text, why are you doing opera?" Stern examines the difference between an old and a contemporary score: "When you look at a page of Bach or Handel or Telemann and compare it with a page of Mahler or Shostakovich, the first thing you notice is that the latter have written details almost on every note - an accent here, a crescendo there. The point is you have to listen to the music. It is a language of tension and resolution. So we have to understand the logic of the language. You have to look into the music, under the notes, between the notes. A musician has much more to do, and a singer too - in cadenzas he has to add ornaments, not in order to show off his or her vocal instrument, but to bring out the meaning of the text. I love this music, because everybody has to be responsible for what is going on. It makes musicians honest - you can't just follow someone's signs, you have to put yourself into it." This is Stern's second time conducting the Israel Opera. His first was in 2002, when he conducted its production of Mozart's Abduction from the Seraglio. He recalls being left alone artistically: the intifada was then at its height, and the director of the production simply didn't show up. His artistic collaborator this time is a different story. "Jakob Peters-Messer is a director who loves music, and he knows the score very well," Stern says. "Even though we have very different ideas, we can talk. It's a pleasure." The American-born Stern works mostly in Europe and is involved with both modern and early instruments. "What interests me is making music live; it makes no difference if it is baroque or late 20th-century pieces," he says. He's come to Israel almost every year since 2001, "not only because of my parents' tradition [he is the son of violinist Isaac Stern, whose support of Israeli musicians cannot be overestimated]. I just enjoy working here. By doing early music, I am as far as possible from my father, who hated period instruments. But the more I do it the closer I come to his ideals, because he was very aware of little details and nuances." Handel wrote during the heyday of the castrato performers - men who had been castrated in their youth to preserve their high voices - and his score for Julius Caesar in Egypt (1723) contains two principal roles written for the castrato voice: those of Caesar and of Cleopatra's brother, Ptolemy. As singers so specially unequipped are mercifully no longer available, baroque operas nowadays rely on either mezzo-sopranos or countertenors. This production alternates between the two, with mezzo-soprano Hadar Halevi and contertenor Yaniv d'Or (brother of popular high-pitched vocalist David d'Or) taking turns as Caesar. Yaniv also alternates with fellow countertenor Brian Asawa in the role of Ptolemy. In the straighforward libretto of this version of the historical tale, both siblings vie for the Roman conqueror's favor, Cleopatra through her feminine charms and Ptolemy by presenting Caesar with the head of his arch-enemy, Pompey. Hebrew and English surtitles will be projected in the production that opens Saturday night and runs through July 7 at the Opera House, Tel Aviv Performing Arts Center, Shaul Hamelech 19, (03) 692-7777.