No moon was higher, no ocean deeper, than when Ella Fitzgerald measured them.

Mack the Knife was never sharper than in her hands, and Miss Otis's regrets were never more heartfelt than when Fitzgerald extended them.

Over the weekend, American popular song turned blue when Ella Fitzgerald passed away at the age of 79. She was not just a singer, of course, but The Singer, the best and most loyal friend a good song could ever hope to have. It was Fitzgerald who almost single-handedly elevated the American popular song to the status of art in the tradition of Italian bel canto and German lieder. In the process, she helped define jazz as "America's classical music." And she was the focus of a nation's pride in a native art form.

Modest and shy despite her fame and achievement, Fitzgerald was an intensely private person who somehow remained out of the public eye even as she was omnipresent in the public ear. Beloved by fans, fellow musicians and critics around the world for almost 60 years, she was one of the few artists able to balance popular music and jazz without sacrificing the essential qualities that make each distinctive. From ballads to bebop, Fitzgerald could sing it or swing it with a grace and vitality that set her apart from the handful of other seminal singers of the 20th century.

In 1957, Duke Ellington composed a musical "Portrait of Ella Fitzgerald" that included movements titled "All Heart" and "Beyond Category." Both descriptions were accurate, deserved and uncontested, as was the veneration and love that flooded Fitzgerald from around the world. The acclaim was as long-standing as her gift for song, and Fitzgerald was so consistent for so long that her best qualities -- warm vocal elegance, youthful vitality, infallible pitch, an impeccable sense of rhythm -- eventually were taken for granted.

People sometimes forget that Fitzgerald was born only two years later than the only other female singer of similar iconic stature, Billie Holiday, but outlived her by 27 years. Holiday seems ancient history, while Fitzgerald's voice echoes from just yesterday. Even age and illness could not dampen its innate ebullience, which the late jazz critic Martin Williams once called "a girlish glisten . . . the stuff of joy."

In the 1930s Fitzgerald was dubbed the First Lady of Swing, and in the early '40s she became First Lady of Song: Both titles fit her well. Her pitch was so true, her intonation so perfect, that band members could tune up to Fitzgerald's voice; and her rhythmic imagination, sense of swing and knowledge of harmony were the envy of fellow musicians, particularly in the bebop era, when she lifted scat singing from its novelty origins.

But Fitzgerald will best be remembered for the landmark series of songbooks in which she explored and championed the work of the American composers and lyricists Cole Porter, Duke Ellington, George and Ira Gershwin, Rodgers and Hart, Irving Berlin, Jerome Kern, Harold Arlen and Johnny Mercer. She gave their songs simple, straightforward readings devoid of the embellishments and mannerisms many jazz singers inflicted on such material. As one critic noted, Ellington, Gerswhin et al., were the architects of popular song, and Fitzgerald came to inhabit their work, not to renovate.

Little wonder they loved her. Richard Rodgers praised Fitzgerald's "intimacy, naturalness and realism -- she portrays the songs, she does not betray them." Ira Gershwin went even further, admitting, "I never knew how good our songs were until I heard Ella Fitzgerald sing them." He wasn't the only one to feel that way.

Beyond her impeccable taste, Fitzgerald had all the right tools: a three-octave-plus voice that was silvery smooth and flexible in its flights from smoky alto to keening soprano. She had an instinct for the most expressive note, and could find it even in the heat of improvisation.

Fitzgerald was not without her critics, who postulated "emotional distance" and slammed her for not investing her material with the naked emotional pain of Holiday, Frank Sinatra or Judy Garland, or the festering anger of Sarah Vaughan and Carmen McRae. They claimed Fitzgerald never understood, much less revealed, the deeper meaning of the lyrics she sang, that she seldom addressed "the dark stuff."

In truth, there was no need for Fitzgerald to take that journey, though she suffered the blues of loneliness for much of her long life. She was never as tempestuous as Vaughan or McRae, never as self-destructive as Holiday, and so she could treat her material as art, not autobiography. Many composers loved her for her discipline and classicism. Yet there were always pleasure and compassion in her singing -- and a measure of hope.

The roots of the Fitzgerald legend are well known, particularly how in 1934, the painfully shy teenager was talked into entering the weekly talent contest at Harlem's fabled Apollo Theater -- as a dancer! And how, after a spectacular dance performance by two sisters, she stepped onto the stage only to experience cold feet and shaky knees until the emcee coaxed her into singing. An unprepared Fitzgerald turned to a song by one of her idols, Connee Boswell; her imitation of Boswell's "The Object of My Affection" helped her win the $25 first prize and the audience's heart.

It also marked the end of Fitzgerald's hoofing career, though she always remained a dancer in song, whether in graceful light-on-her-feet ballads or jitterbug scats. After the Apollo win Fitzgerald caught the eye and ear of swing band leader and drummer Chick Webb, who soon became her mentor and legal guardian (her mother had died the year before). Webb, whose orchestra was the house band at New York's Savoy Ballroom, proved to be a major influence, particularly in terms of rhythm. (His advice to Fitzgerald was "Always be with the beat!")

Though Fitzgerald's voice was still young and her skills far from developed, she made an immediate impression. Her very first review, by George T. Simon in the May 1935 issue of Metronome, predicted that "Miss Fitzgerald should go places." Another review from that period noted that "her voice is seemingly tinged with honey, and she sings with a rhythmic tempo that puts her over with a bang." Fitzgerald was all of 17 at the time.

She started her recording career with Decca in 1935 -- her catalogue now contains more than 250 titles -- and achieved mass popularity three years later with "A-Tisket, A-Tasket," a sweetly rambunctious update on the old children's rhyme. It went to No. 1 -- this in an era when there was no Maginot line between jazz and pop -- and became one of the biggest hits of the time, selling more than a million copies (Fitzgerald's only million-seller, incidentally).

Fitzgerald also scored in 1936 with "(If You Can't Sing It) You'll Have to Swing It," better known as "Mr. Paganini." It became one of her signature songs, but Decca had little imagination and saddled her with pop ditties and novelty tunes, clearly hoping to repeat the success of "A-Tisket, A-Tasket." Those hopes were never realized, even after Fitzgerald spent a few years fronting Webb's band -- renamed Ella Fitzgerald and Her Famous Orchestra -- after Webb's death in 1939.

Though her 20-year recording career with Decca was disappointing, Fitzgerald continued to make a name for herself through live performances, where she had more control over both material and musical setting. In the '40s, she first hooked up with jazz entrepreneur Norman Granz, who added her to his crucial Jazz at the Philharmonic concert series and encouraged collaborations with Ellington, Basie and, later, Armstrong and Sinatra, and even later with pianist Peterson and guitarist Pass.

It was during the '40s -- the early days of bebop -- that Fitzgerald perfected what came to be known as scat singing, improvising wordlessly (and often with nonsensical syllables) to simulate an instrumental solo. Fitzgerald, who once wished she had been born a tenor sax player, used her musical knowledge to match what she heard the horns doing.

The technique in itself was hardly new, but it was innocuous until bebop woke everybody up with its complicated modern harmonies and rhythmic turns, which presented few problems to a singer blessed with an excellent ear, great musicianship and an expansive imagination. She honed her craft in Dizzy Gillespie's bebop band, which she fronted at a time when many swing-era musicians and almost all the swing-era vocalists were shunning the new music.

From the start, Fitzgerald could swing and improvise better than any of her peers, and scat became one of her trademarks on songs like "Flying Home," "How High the Moon" and "Lady Be Good." Onstage, Fitzgerald was never a "guest vocalist" but one of the guys, taking her break with a voice instead of an instrument and not only keeping up but leading the charge, wowing musicians and audiences alike with her stamina and wit (folks loved Fitzgerald's interpolations of familiar melodies and other players' musical quirks). Lester Young, who had dubbed Billie Holiday "Lady Day," called Fitzgerald "Lady Time" in acknowledgment of her improvisational skills.

Recording justice was finally achieved in 1955 when Granz was able to extricate Fitzgerald from her Decca contract. He started Verve Records specifically for her and issued not only the songbooks but a steady stream of studio and concert recordings that better reflected the singer's strengths and passions. The eight songbooks issued between 1956 and 1964 remain the essential canon of American popular song.

The Verve era lasted more than a decade, and though Granz would rescue Fitzgerald again in the '70s when he started Pablo Records, she too fell victim to the '60s rise of rock and the concurrent decline of pop and jazz. Still, Fitzgerald was game enough to address songs by Harry Nilsson, Randy Newman, Smokey Robinson, Marvin Gaye, Carole King and the Beatles (her last "hit" was a 1964 swing band version of "Can't Buy Me Love"), but she never attempted songbooks for those writers, and her strength remained the standards of another era.

Over the last 25 years, Fitzgerald did not have it easy. She had many health problems -- from cataracts to diabetes -- ironic for someone with no vices and a nose-to-the-grindstone commitment to work. It was as if, with little emotional sustenance in her private life, Fitzgerald had come to live for and through her art. Fellow musicians always talked about her unbounded energy and enthusiasm. In fact, only serious health problems could slow Fitzgerald down. As she herself put it on "Ain't Nobody's Business": "When the voice is boppin'/ Tain't no need in stoppin' . . . "

She ignored medical advice to slow down. In September of 1986, she underwent quintuple-bypass surgery, which took Fitzgerald off the road for nine months, her longest absence in 50 years. She consented to a radical reduction in her concert appearances, often performing from a stool.

In 1984, Fitzgerald recorded "The Best Is Yet to Come," and though it won a Grammy, her best had already come. Her last album was 1990's "All That Jazz" (which also won a Grammy, her 13th). Finally, ongoing problems with diabetes led to the amputation of both legs in the fall of 1993, a development not announced until April of the following year.

Over the last decades, Fitzgerald had already made adjustments for the changes in her voice (lowering keys, minimizing the vibrato, doing more genial scatting to compensate for the longer-held notes of ballads). "Lady Be Good" was transformed into a pensive lullaby, but even as she was adapting to her limitations, Fitzgerald never abandoned her youthful charm. Her interior spirit ushered away the frailness, and she sounded beyond age. In one of Fitzgerald's last major interviews, around her 70th birthday, I asked how she felt when people described her as the greatest singer of our times. She was not embarrassed by the question, but insisted, "I never thought that about myself. All I wanted to do, after I found out people liked me, was to sing. And I wanted that love. That was me giving you something and you giving me something in return. From here." Fitzgerald pointed to her heart.

A week or so after the article appeared, I received a note, something of a miracle since the address and the return were both written in an illegible scrawl. So was the card inside, and the only I way I figured out who it was from was the "Beverly Hills, CA" postmark. It was from Ella Fitzgerald, whose arthritis and eyesight were so bad at the time that writing the note must have been excruciating. I never did make out most of what Fitzgerald wrote, but I knew right away what her intentions were.

So did the millions of people who came to know Ella Fitzgerald's voice, her song, her gift and her character. At Ellington's funeral in 1974, the grieving singer had said, "You knew his death had to come sometime. . . . I don't think people realize even yet how great the man was."

The same is true of Ella Fitzgerald. She sang the standards and set the standards and her achievement will never be surpassed.

In the last years of her career, Fitzgerald was often led onto the stage to her seat, which always prompted standing ovations. With typical humor, she'd express her appreciation, adding, "I hope you feel that way when I finish." People did, and people will.

To quote one of your own standards, Ella, there will never be another you. Legacy of a Master

"The Complete Ella Fitzgerald Songbooks" (Verve, 1993). This 16-CD box set collects all eight songbooks and looks exactly like what it is: the cornerstone to any appreciation of American popular song, a definitive reference source because Fitzgerald was faithful to the intentions of the composers (who received equal star billing). The individual songbooks are also available -- the best are the Ellington and Gershwin collections, since they, too, straddled the fence between jazz and popular music. There is also a "Best of the Songbooks" for those inclined to Whitman's Samplers. Another fine songbook predates the series: "Ella Sings Gershwin," duets with pianist Ellis Larkins.

"Ella Fitzgerald: 75th Anniversary Celebration" (Decca Jazz/GRP). A two-CD collection featuring 30 songs from her 20-year Decca career. With more than 250 albums to her name, even Fitzgerald would have been be pressed to identify the best. Among those of enduring appeal to ballad lovers: "Like Someone in Love" (1957), "The Intimate Ella" (1960) and a ballad collection drawn from the "Complete Songbooks."

Fitzgerald also recorded many albums with such illustrious peers as Louis Armstrong, Duke Ellington, Count Basie and, later on, Oscar Peterson and Joe Pass. Many of the early works have been reissued on CD; among the best are "Ella and Louis" (from 1956); Ella and Louis doing a jazz-focused "Porgy and Bess" (1957); "Ella Fitzgerald and Louis Armstrong" (1972); "Ella and Basie: On the Sunny Side of the Street" (1963); "Ella & Basie: A Perfect Match" (1980); "Ella at Duke's Place" (1965); "Ella and Oscar" (1975); "Fitzgerald and Pass . . . Again" (1976); and "Speak Love" (1983).

Among her many live albums, these are recommended: "Ella Fitzgerald at the Opera House" (1957) and "Mack the Knife: The Complete Ella in Berlin" (the 1960 concert in which Fitzgerald forgot the lyrics to "Mack the Knife" and won the audience's heart with her skillful, and hilarious, recovery and improvisations). A Fitzgerald Sampler

To sample different aspects of Ella Fitzgerald's music, the Post offers three sound bites. They can be heard by calling Post-Haste at 202-334-9000 and pressing the number listed after each selection.

To hear Fitzgerald's 1938 breakthrough hit, "A-Tisket, A-Tasket," press 8151.

To hear the Cole Porter ballad, "Miss Otis Regrets," recorded in 1956, press 8152.

To hear Fitzgerald scatting on George and Ira Gershwin's "Oh, Lady Be Good," recorded in 1957, press 8153. CAPTION: Ella Fitzgerald with fellow jazz icon Dizzy Gillespie in 1947. CAPTION: Ella Fitzgerald in 1981, marking her 10th anniversary in Memorex ads. CAPTION: The singer in 1974 with fellow members of music's royal family, Frank Sinatra and Count Basie. CAPTION: Fitzgerald in the '40s, making an impression on the American popular song.