Beverly Sills, whose radiant soprano and vibrant personality made her “America’s Queen of Opera,” as Time magazine called her in 1971, died last night. She was 78.

It had been revealed a few days ago that Ms. Sills was gravely ill with inoperable lung cancer. The singer, who never smoked, died about 9 p.m. at her Manhattan home, said her manager, Edgar Vincent.

Ms. Sills, who retired from the stage in 1980, sang some 70 roles in her career. The two opera companies with which she was most closely associated were the New York City Opera and the Opera Company of Boston, headed by Sarah Caldwell. Ms. Sills was a mainstay of the latter throughout the 1960s.

Both companies were operatic underdogs, which contributed to Ms. Sills’s democratic, one-of-us image, as did the fact she spent most of her career performing in the United States. Her friendly, extroverted manner helped popularize opera in this country. This was equally true during her performing career and then as an administrator at City Opera, New York’s Lincoln Center, and the Metropolitan Opera.

Among Ms. Sills’s most notable roles were Cleopatra, in Handel’s “Julius Caesar” (her breakthrough performance, at City Opera, in 1966); Massenet’s “Manon”; Violetta , in Verdi’s “La Traviata”; and the title role in Douglas Stuart Moore’s “The Ballad of Baby Doe.”

Ms. Sills’s soprano was a lyric coloratura, prized for its lightness, agility, range, and skill at ornamentation. Later in her career she took on several spinto (or heavier-voiced) roles, most notably the three Tudor queens in Donizetti’s operas: Elizabeth I, in “Robert Devereaux,” Anne Boleyn, in “Anna Bolena,” and Mary Stuart, in “Maria Stuarda.”

For Elizabeth, Ms. Sills spent two hours being made up and wore a gown that weighed 55 pounds. “Elizabeth was not my finest role, but it was my finest accomplishment,” she said in a 2000 Boston Globe interview. “I couldn’t depend on my dimples to get me through.”

More than dimples contributed to Ms. Sills’ impact on stage. She had a helm of titian hair and statuesque physique and boasted impressive acting skills. Performance for her was a matter of interpretation as well as music. “Before she undertakes a role, Miss Sills exhausts the literature about it,” the critic Winthrop Sargeant wrote in his 1973 book, “Divas. Having “absorbed all the available historical and biographical data, she starts going over the music at the piano.”

Opera did not lack for legendary sopranos during Ms. Sills’s heyday, the 1960s and 1970s. Maria Callas, all intensity and hubris, could have stepped out of Greek tragedy. Leontyne Price had an unmatched regal presence. Joan Sutherland was hailed as “La Stupenda.”

In contrast, Ms. Sills was known as “Bubbles.”

It is commonly assumed the name sprang from her warmth and ebullience. In fact, the nickname was bestowed at birth because of the foamed saliva on her lips. “Bubbles” couldn’t have been topped as a term of affection.

As much as her superlative singing, it was Ms. Sills’s lack of pretense that helped make her such a cherished figure. A down-to-earth diva, she was more big sister or friendly aunt than temperamental prima donna — “the sort of woman,” Michael Steinberg wrote in his Globe review of her 1975 debut at the Metropolitan Opera, “who actually catches the bouquets that are thrown at her across orchestra pits and footlights.”

Long before the Three Tenors, Ms. Sills braided together opera and popular culture. She clowned with Carol Burnett in an Emmy-nominated television special and subbed for Johnny Carson on “The Tonight Show.” She had her own talk show on NBC, “Lifestyles with Beverly Sills,” and for many years hosted PBS’s “Live from Lincoln Center” broadcasts.

Show biz came naturally to Ms. Sills, who never attended a conservatory. Born Belle Miriam Silverman in Brooklyn on May 25, 1929, she first sang in public at 3, winning a Most Beautiful Baby contest with a rendition of “The Wedding of Jack and Jack.” Her parents were Morris Silverman, an insurance salesman, and Sonia (Bahn) Silverman.

“When I was 4 or 5, everybody’s mother was convinced their daughter was the next Shirley Temple,” Ms. Sills said last year in a Newsday interview. “I was the operatic Shirley Temple.”

Ms. Sills regularly performed on a Saturday morning radio show, began voice lessons, and sang in a 1936 movie short, “Uncle Sol Solves It.” At 10, she won first place on a network radio program, “Major Bowes’ Amateur Hour,” the “American Idol” of its day.

“I was self-supporting as a singer from the time I was 15 years old,” Ms. Sills remarked in that 2000 Globe interview. Promoted as “the youngest prima donna in captivity,” Ms. Sills recalled traveling “around the country on a bus, singing every night and making $125 a week and living on Dinty Moore beef stew — I didn’t have a weight problem in those days!”

Joking about her size was indicative of Ms. Sills’s forthrightness and candor. Her husband, Peter Greenough, came from a wealthy background (his family owned The Cleveland Plain Dealer newspaper), and she acknowledged how that helped her to thrive in a demanding career while raising a family.

She met Greenough in Cleveland while on a 1955 tour with City Opera. “He winked, which I thought was pretty corny,” Ms. Sills told The Christian Science Monitor in 1985, “but it worked.” Greenough died last year.

Ms. Sills had three stepchildren from Greenough’s previous marriage and two children with her husband: a son, Peter Jr., who is autistic and mentally retarded, and a daughter, Meredith, who suffers from multiple sclerosis and who is deaf. For many years, Ms. Sills served on the boards of the March of Dimes and the Multiple Sclerosis Society.

“It was an ironic trick of the gods to give me a daughter who couldnt hear me sing,” Ms. Sills said on a PBS special last year devoted to her career, “Beverly Sills: Made in America.” “It affected my singing. The best times I had were moments on stage. To be able to pretend to be somebody else for three hours was such a relief.”

Largely because of her family situation, Ms. Sills spent most of her career in the United States — something highly unusual for someone with her gifts. “I’m a revolutionary,” Ms. Sills said in a 1975 Opera News interview, “because I proved that one can have a great career without the Met and, in this country, without European approval. Few Americans have made it really big at home, and my career is typically American — yet so atypical. I went [to Europe] as a prima donna [who was] stamped first in America.”

A revolutionary needs to be determined, and Ms. Sills was. She auditioned nine times at City Opera before making her debut there, in 1955. When it appeared the company might not cast her in “Julius Caesar,” she announced, “If I don’t get the Cleopatra, I’ll hire Carnegie Hall and sing five Cleopatra arias just to get her out of my system, because, by God, I’m going to sing Cleopatra in New York!”

At a 1994 tribute, the violinist Isaac Stern described Ms. Sills as “this steamroller that travels around like a lady.”

Ms. Sills had a rich and longstanding connection with the Boston area. She lived in Milton during much of the ’60s. (Her husband was the Globe’s financial columnist from 1961 to 1969.) Ms. Sills also had a summer home on Martha’s Vineyard for many years.

“Manon” was her debut performance with the Opera Company of Boston. She also appeared as the Queen of the Night in Mozart’s “The Magic Flute;” with Placido Domingo in Rameau’s “Hippolyte et Aricie”; in the US premiere of Luigi Nono’s “Intolleranza” (a rare foray into contemporary music); her only Gilda, in Verdi’s “Rigoletto”; and the title roles in Donizetti’s “Lucia di Lammermoor” and “La Fille de Regiment.”

Ms. Sills also performed several times with the Boston Symphony during Erich Leinsdorf’s tenure as music director — most memorably in a concert performance of the original version of Richard Strauss’s “Ariadne auf Naxos,” as Zerbinetta. At one point, the score calls for the character to sing an F-sharp above a high C — a note “only audible to dogs,” Ms. Sills liked to joke.

Ms. Sills recorded 18 operas and several recitals, twice winning Grammy Awards. Still, the recording studio never meant as much to her as the stage. “I like the audience,” she told Opera News in 1975, “and I’m not thrilled by the sight of a microphone.”

Perhaps her most memorable stage performance came when she finally made her Met debut, in Rossini’s “The Siege of Corinth.” Rudolf Bing, the Met’s famously autocratic director, had said of Ms. Sills a few years before, “I have heard her sing, but not lately, and I can’t remember in just what.” She made her debut after Bing resigned. When the curtain rang down that night, Ms. Sills received 26 curtain calls and the standing ovation lasted 18 minutes and 20 seconds.

She was only 50 when she sang onstage for the last time. “I wanted people to say, ‘You left too soon,’ not ‘You left too late,’ ” she said in a 2002 Globe interview. She professed never to regret the decision. “Since I retired,” she added, “I’ve been singing nothing but ‘Happy Birthday,’ and now even my family doesn’t ask me to do that.”

Retirement from the stage did not mean retirement from opera. Ms. Sills served as general director of City Opera from 1979 to 1989; chairwoman of New York’s Lincoln Center for the Performing Arts from 1994 to 2002; and cairwoman of New York’s Metropolitan Opera from 2002 to 2005. Ms. Sills was the first woman to hold each of those positions.

“While I no longer do what made me famous,” Ms. Sills said in her 1985 Christian Science Monitor interview, “I’m still pretty much of a driving force in the same area.”

Ms. Sills received the nation’s highest civilian honor, the Presidential Medal of Freedom, in 1980. A Kennedy Center honoree in 1985, she was a recipient of the National Medal of Arts in 1990. She also won two Emmy Awards.

“Oh, I always knew I was going to be an opera star,” Ms. Sills said in that Monitor interview, “not just an opera singer, an opera star. The moment I saw Lily Pons on the stage, I knew that.” She was 8.

In addition to her children, both of Manhattan, and stepchildren, Lindley Thomasett of Bedford, N.Y., Nancy Bliss of Woodstock, N.Y., and Diana Greenough, of Lancaster, Mass., Ms. Sills leaves a brother, Stanley.