Cory Weaver/San Francisco Opera

A scene from "Heart of a Soldier," featuring William Burden as Daniel J. Hill and Thomas Hampson as Rick Rescorla

Last week, the San Francisco Opera was rehearsing a troublesome passage in “Heart of a Soldier,” an opera based on real events on Sept. 11, 2001, which makes its world premiere Saturday at the War Memorial Opera House.

The conductor, Patrick Summers, stopped the music and consulted with the opera’s composer, Christopher Theofanidis. “Please erase the note ‘the beat remains the same,’” Summers told the orchestra members. “It does not remain the same.”

The beat of American life has not remained the same either since Sept. 11, when terrorist attacks traumatized the country. And for 10 years, artists have sought to make sense of that day through stories, paintings and music, searching for a universal message of human connection and hope. It has been a daunting task.

“You risk a lot by engaging this subject,” Theofanidis said. “But do you talk about something that’s really serious to you or not?”

A story of love and heroism on Sept. 11, “Heart of a Soldier” is based on James B. Stewart’s nonfiction book by the same name. It focuses on Rick Rescorla, who, as second vice president for corporate security at Morgan Stanley, shepherded all but six of his company’s 2,700 employees in their World Trade Center offices to safety that day.

On a final sweep through the South Tower, Rescorla was killed when the building collapsed.

“You worry about it being vulgar or, even worse, disrespectful,” Theofanidis said of the challenge in creating the opera. “It’s a matter of finding the right way and right tone that you yourself can live with.”

Theofanidis, 43, has made Rescorla’s story real for himself with the dynamic, melodic music that has defined his career.

“I write very tonal, accessible music,” he said. “The things that I tend to go around humming are the things I try to bring to my own writing.”

That oversimplification is characteristic of the humble, gentle-spoken composer. Theofanidis, who teaches at Yale, has composed a range of chamber and orchestral works, oratorios and solo works with bold Romantic melodies and sly modernist twists, evoking his formative influences, Prokofiev and Bartok.

One critic called Theofanidis’ 2002 two-act opera, “The Thirteen Clocks,” which is based on a James Thurber story, “fabulously shimmering.”

Theofanidis, said San Francisco Opera’s general director, David Gockley, “has the ability to write lyrically and to write theatrically.”

It was Gockley who had introduced Theofanidis to Stewart’s book, in 2004, when Gockley was general director of Houston Grand Opera. Gockley had been following Theofanidis’ career for years, thanks in part to his executive assistant at Houston, Theofanidis’ mother.