Lili Chookasian, an American singer who debuted with the Metropolitan Opera at age 40 and over the next two decades became known as one of the most blazingly powerful contraltos of her generation, died April 10 at her home in Branford, Conn.

She was 90 and had congestive heart failure, said her daughter Valerie Klutch.

Ms. Chookasian (pronounced choo-KAY-see-an) was a middle-aged mother of three and a survivor of breast cancer when she stepped onto the stage at the Met, one of the world’s premier opera houses.

Her March 9, 1962, appearance in Amilcare Ponchielli’s “La Gioconda” marked a high point in a career that was to unfold with 290 performances with the Met.

Relatively small in stature, she might have seemed ill-suited to embody the robust roles written for contraltos, whose voices are the deepest in the female register.

Lili Chookasian, a celebrated American contralto who sang with the Metropolitan Opera for more than two decades, died April 10. She was 90. She is shown here in costume for Gian Carlo Menotti's opera “The Last Savage.” (Courtesy of The Metropolitan Opera Archives )

“But the sound that emerged from that body,” music scholar Brian Kellow wrote in Opera News upon her death, “was enormous — dark, with a power and cut that were exhilarating and . . . quite terrifying.”

At the time of her Met debut, Ms. Chookasian had behind her two decades of recital experience. But she had performed in only a handful of operas. A year earlier, she had turned down a contract with the Met because she did not wish to uproot her husband and children from their Chicago home.

Cast alongside her in the debut performance were three major opera stars of the day: Franco Corelli, Zinka Milanov and Robert Merrill. But it was Ms. Chookasian whose name appeared in the headline of the New York Times review the following day.

“She had everyone muttering ‘a real contralto,’ ” music critic Eric Salzman wrote of Ms. Chookasian’s performance as the heroine’s blind mother. “She has a dark, rich voice, used with great sensitivity and with a powerful feeling.”

A year after that triumph, Ms. Chookasian moved her family to New York and became a principal soloist with the Metropolitan.

She was most associated with the works of the 20th-century composer Gian Carlo Menotti. Singing at the Met in the 1964 U.S. premiere of his opera “The Last Savage,” she took on the role of the “monstrously fat” Maharanee with “great good spirits,” wrote Times music critic Harold C. Schonberg. A year earlier, she played Mme. Flora in a New York City Opera production of Menotti’s “The Medium.”

Her most celebrated roles also included Ulrica, another fortuneteller, in Verdi’s “A Masked Ball,” Amneris in his opera “Aida” and Mamma Lucia in Mascagni’s “Cavalleria Rusticana.”

Ms. Chookasian owed her career in part to two conductors, one who wielded a baton and the other a ticket punch. The first was Thomas Schippers, the late American director of orchestras including the New York Philharmonic. In the late 1950s, after hearing a recording of her performance of Bellini’s “Norma” in Little Rock, he invited her to come to New York for an audition.

The second of the conductors who helped her was taking tickets on a train. Ms. Chookasian had accepted Schippers’s invitation and agreed to travel to New York from Baltimore, where she was studying with the soprano Rosa Ponselle. But when she arrived at the train station, she found that her money would take her only as far as Trenton, N.J. On the train, when she told the conductor that she was headed to a music audition, he let her ride all the way.

In 1961, Schippers hired Ms. Chookasian as a soloist in Prokofiev’s “Alexander Nevsky,” a bombastic Russian cantata written in 1938 as a motion-picture score. The performance, which Schonberg called “brilliant,” helped lead to her recruitment by the Metropolitan.

In addition to her operatic performances, Ms. Chookasian continued her solo career with orchestras including the New York Philharmonic under Leonard Bernstein and the Philadelphia Orchestra under Eugene Ormandy.

Her most important numbers included Mahler’s Symphony No. 2, known as the Resurrection Symphony, and his “Das Lied von der Erde” (“The Song of the Earth” ). Her repertoire ranged from the “Requiem” by Verdi, a 19th-century Italian composer, to “Gurre-Lieder” by the avant-garde 20th-century Austrian composer Arnold Schoenberg.

In 1965, Ms. Chookasian played Erda in Wagner’s “Das Rheingold” at the Bayreuth Festival in Germany, then directed by the composer’s grandson Wieland. The production called for some rather edgy costumes. Citing her respect for Wieland Wagner’s artistic vision, Ms. Chookasian obliged.

“I would do anything for him,” she told Time magazine.“Why, I even took a curtain call wearing that black leather costume that opened up to display two enormous leather breasts. . . . And I didn’t even blush.”

Lillian Phoebe Chookasian was born Aug. 1, 1921, in Chicago to a machinist and a homemaker, both Armenian immigrants. Her paternal grandparents were killed in the slaughter of Armenians during World War I, her daughter said.

Convinced of Ms. Chookasian’s talents, her mother took her to an audition for the popular radio program “Hymns of All Churches,” which made Ms. Chookasian a featured soloist when she was a teenager. Later, she sang in Handel’s “Messiah” with the Mormon Tabernacle Choir and with the Chicago Symphony Orchestra.

In 1959, she made her opera debut as Adalgisa in “Norma” in the Arkansas State Opera performance that helped bring her to Schippers’s attention.

After her retirement from performing in 1986, Ms. Chookasian pursued a second career as a voice teacher at Yale University’s School of Music.

Her husband, George Gavejian, died in 1987 after 46 years of marriage.

Survivors include three children, Valerie Klutch of Branford, John Gavejian of Mahwah, N.J., and Paul Gavejian of Chappaqua, N.Y.; 11 grandchildren; and eight great-grandchildren.

In 1969, a reporter noted that Ms. Chookasian seemingly managed to do everything — bring up her children, run a household and achieve a top-flight career in opera. How did she do it?

“I don’t want to be left out of anything, really,” Ms. Chookasian said. “I’ve come to the conclusion that if you’re busy or not, you’ll find time for things that are important to you.”