Leon Kirchner; Harvard teacher wrote bold, daring music, won Pulitzer; at 90

Mr. Kirchner’s music was bold and urgent, often charged with a smoldering intensity and a powerful expressive drive. His Third String Quartet won the Pulitzer Prize in 1967, and he was the recipient of many of his field’s highest honors.

“An artist must create a personal cosmos,’’ he once declared, “a verdant world in continuity with tradition.’’ His body of work - which included solo piano pieces, four quartets, two trios, concertos and orchestral works, and one opera - powerfully bore out that vision.

It was a musical cosmos in sway to its own set of original rules. Mr. Kirchner adopted a challenging modernist language but avoided the strict 12-tone methods that became fashionable in the post-war decades.

The burning expressive passion in his music made it an uneasy fit in the academic world yet Mr. Kirchner’s work also placed far more demands on everyday concertgoers than the facile variations of neo-romanticism whose ascendance he lived to see.

“His music can be harrowing to listen to,’’ the pianist Robert Levin said in a recent phone interview. “It shatters and transforms us. Leon gave us self-portraits without any mercy to himself. He showed the anguish within and did not flinch from it. The number of composers who are able or willing to do that is not large.’’

The pianist Russell Sherman, speaking by phone, also reflected on Mr. Kirchner’s art: “His music was heated and restless in its way of trying to find and surmount the passions and confusions of life, continuously probing and attacking them, and therefore creating such a wonderful intensity.’’

Mr. Kirchner was born into an immigrant Jewish family in Brooklyn but moved at an early age to Los Angeles, arriving at a time when the city had become home to a number of Europe’s most prominent composers, including Arnold Schoenberg. Mr. Kirchner also studied with Ernest Bloch and Roger Sessions, but it was Schoenberg who became his most influential teacher and, in later decades, an ethical lodestar whose integrity he deeply admired.

Even as a young composer, the force of Mr. Kirchner’s music was unmistakable. In a 1950 review in the journal “Notes,’’ composer Aaron Copland wrote that “the impression carried away from a Kirchner performance is one of having made contact not merely with a composer, but with a highly sentient human being; of a man who creates his music out of an awareness of the special climate of today’s unsettled world. Kirchner’s best pages prove that he reacts strongly to that world; they are charged with an emotional impact and explosive power that is almost frightening in intensity.’’

Over the years, Mr. Kirchner’s music attracted several prominent champions, including cellist Yo-Yo Ma and conductor James Levine, who last year led the Boston Symphony Orchestra in the premiere of Kirchner’s orchestral work “The Forbidden.’’

Mr. Kirchner came to Harvard in 1961, after teaching at Mills College, and eventually assumed an endowed chair previously held by the composer Walter Piston. At Harvard he became a revered pedagogue and the founder of a highly regarded course, Music 180, that creatively combined the performance and the analysis of music. Among the early students in the course were Ma, violinist James Buswell, and violinist Lynn Chang.

“As performers,’’ said Chang, “we are mostly outside the score looking in, but, as a composer, Leon had the idea of looking from the inside of the score outward. It was a completely different perspective for me and for all the performers there.’’

Robert Levin, the pianist and Harvard music professor who now teaches Kirchner’s storied course, also emphasized how much Kirchner gave to his students.

“Leon’s monument is just as much for those who were fortunate enough to experience him as a teacher,’’ said Levin, “as for those who have been transformed by the urgency and intensity of his music.’’

Producing music of such pointed expressivity seemed to exact a toll on Mr. Kirchner, whose compositional process could be slow and difficult. For almost two decades, he labored over the creation of his opera “Lily,’’ based on Saul Bellow’s novel “Henderson the Rain King.’’ An early recording of some of the music raised expectations dangerously high, but the opera received a poor first production, and the 1977 premiere was a failure, with New York Times critic Harold Schonberg tagging the work as “stillborn.’’ Others strongly disagreed and have called for the work to be given another chance.

To many in Boston’s musical public, Mr. Kirchner was best known as the conductor of the Harvard Chamber Orchestra, whose concerts, especially performances of Bruckner and Schoenberg, became essential local events. Mr. Kirchner was such a widely engaged musical presence that some wondered at times whether his concert activities, including extensive piano performance, might be siphoning energy from his work as a composer.

Mr. Kirchner saw it otherwise. “Performing is a level where all the talking and theorizing stops, a completely different way to solve life’s problems,’’ he told a Globe interviewer in 1982. “It’s a test being up there, and it’s important for creative people to be tested. A performer calls upon things in himself that are otherwise dormant, and his whole life process becomes revitalized.’’

In 1949 Mr. Kirchner married Gertrude Schoenberg (no relation to the composer), who died in 1999. Mr. Kirchner leaves his partner, Sally Wardwell; a daughter, Lisa of New York; a son, Paul of Cambridge; a brother, Julius of La Jolla, Calif.; and a granddaughter.

Services will be private.

On one occasion in the 1970s, Mr. Kirchner wrote to the Globe congratulating a colleague with words that might have been applied to their author: “We might cheer you,’’ he wrote, “simply for standing erect after all these years under the heavy weight of public honor, constant effort, and that special travail which comes to all who have the temerity to orbit some inner region of the soul.’’