Composer Conrad Susa at the Kennedy Center in 1998. Mr. Susa, sometimes described as a “postmodern” composer, died Nov. 28 in San Francisco. He was 78. (Tom Allen/The Washington Post)

Conrad Susa, a prolific composer for voice and stage whose works include the widely produced 1973 opera “Transformations,” based on poet Anne Sexton’s retelling of Grimm’s fairy tales, died Nov. 28 at his home in San Francisco. He was 78.

He had a long period of decline following a serious fall, said Byron Adams, a University of California at Riverside musicologist who is an executor of Mr. Susa’s estate.

A longtime professor of composition at the San Francisco Conservatory of Music, Mr. Susa wrote five operas, including “The Dangerous Liaisons,” based on the 18th-century French epistolary tale of erotic scheming by Pierre Choderlos de Laclos.

His musical language was polyglot in its inspirations —“Transformations,” for example, draws from Bach, Samuel Barber and the bossa nova, among other influences — but Mr. Susa wove them together into his own distinctive sound.

“He was in a way the first postmodern composer,” Adams said Monday. “He would select from various types of genres anything he needed to be expressive.”

Known for his tendency to write and rewrite nearly to curtain time, Mr. Susa said composing operas was not for the faint of heart.

“I myself can only do it every five years,” he told the Los Angeles Times in 1994, when “Liaisons” received its world premiere at San Francisco’s War Memorial Opera House, starring Frederica von Stade, Renee Fleming and Thomas Hampson. “It takes that long to forget how truly hair-raising it can be.”

Mr. Susa also wrote more than 200 theater scores during a career that included 35 years as resident composer for San Diego’s Old Globe Theatre.

As a choral composer, he was known for numerous works that have become standard fare in holiday concerts, including “A Christmas Garland” and “Carols and Lullabies.”

His most popular and enduring work, however, was “Transformations,” which was a turning point for Mr. Susa as much as it was for Sexton, the Pulitzer Prize-winning poet and feminist who killed herself in 1974.

Mr. Susa, who was born April 26, 1935, in Springdale, Pa., studied composition at the Carnegie Institute of Technology in Pittsburgh and the Juilliard School of Music in New York, where he earned a master’s degree in 1961. He soon was working for off-Broadway productions.

While in New York, he won a number of honors, including the George Gershwin Memorial Scholarship. In 1972, when Mr. Susa was commissioned by the Minnesota Opera to write “Transformations,” the openly gay composer moved to San Francisco.

He intended only a short stay but remained in the city because of the freedom it offered to explore “the right kind of wildness, as far as I was concerned,” he said this year in an oral history for the San Francisco Conservatory of Music.

“So I left New York to compose ‘Transformations,’ but the change was already beginning in me, and ‘Transformations’ was a product of it.”

The opera, performed chamber-style by eight singers and eight musicians, was based on Sexton’s 1971 collection “Transformations,” which used fairy tales to explore various aspects of womanhood and the conflicts that tormented her.

Mr. Susa chose the poems for the libretto and set the opera in a mental hospital, with Sexton as the narrator. On opening night, the poet sat with Mr. Susa in the front row and, according to Sexton biographer Diane Wood Middlebrook, shouted to him during intermission, “Conrad, you’re a genius!”

It became one of the most frequently produced operas by an American composer.

Andrew Porter, in a review for the New Yorker, wrote that “Transformations” was “one of the brightest and best of recent American operas. . . . Susa’s score is economical, intelligent, witty and alert.”

Mr. Susa’s survivors include two brothers.

Mr. Susa started at San Diego’s Old Globe in 1959 and at first ran the sound system as well as compose music. Writing background scores for Shakespeare was often seen as incidental to the acting, but Mr. Susa said he was inspired to create music that serves as “part of the unconscious world of the play.”

“I get to bring on a king or two; I get to provide music for his coronation, send a lot of troops into battles, create the weather,” he told the Times in 1988. “I’ve sunk a few ships; I’ve helped precipitate some rebellions. If I wrote music just to express things in my life, I wouldn’t have that range.”

— Los Angeles Times