The late Ella Fitzgerald showed reserve everywhere but onstage and in the recording studio. In tonight's "American Masters" documentary, "Ella Fitzgerald: Something to Live For," the First Lady of Song admits to her legendary shyness. But once she hits the stage, she says, "it's a different feeling. I get nerve from somewhere; maybe it's because it's something I love to do."

For 60 years, folks around the world loved what Fitzgerald did, which was to sing songs with style, grace, warmth and utter devotion to the lyrics and melody. Songwriters may have loved her just a little bit more for that. Lindy hopper Norma Miller, a friend from Fitzgerald's spectacular entrance--winning an Apollo Theatre amateur contest in 1934--tells director Charlotte Zwerin, "Every singer after Ella adopted her standard, and her standard was the highest."

According to Zwerin's documentary (9 p.m. on Channel 26), it wasn't an easy road to success, and the road that Fitzgerald refused to abandon once she became successful eventually took a terrible toll. That journey began in Newport News in 1917, and began to gain resonance when Fitzgerald and her mother moved to New York; it flirted with disaster when Fitzgerald was orphaned at 15 and briefly ended up in a reformatory.

Fitzgerald's true release came with the Apollo victory at age 17--she'd originally envisioned a dance career, but turned to song after the previous performers brought down the house with a dance number. Soon after, she hooked up with drummer and big-band leader Chick Webb, who became her mentor-protector. It was with Webb that Fitzgerald began to hone her craft as a sweet ballad and swing singer, scoring her first chart-topper in 1938 with the novelty song "A-Tisket, A-Tasket."

After Webb's sudden death in 1939, and the declining fortunes of big bands in the early '40s, Fitzgerald did what many jazz musicians couldn't--she made a seemingly effortless transition from swing to bebop. In a way, she became just another horn, mastering the scat form of vocal improvisation and instrumental mimicry in ways that earned the respect of her peers. At that point, says narrator Tony Bennett, "the final elements of her style were falling in place."

And fans, musicians and critics were falling all over themselves with accolades--Fitzgerald was showered with awards, particularly after she embarked on an extensive series of "songbooks" devoted to masters of American popular song. She became a fixture in prestigious concert halls around the world and proved ubiquitous on television. Zwerin's documentary is rich with expansive excerpts from shows dating from the '50s through the '80s, with Fitzgerald the embodiment of elegant craft and emotional commitment in solo performances of "Summertime" and "Once in a While."

That Fitzgerald was also an enchanting vocal partner is brought out in vintage clips of encounters with Louis Armstrong, Nat King Cole (a spry "It's All Right With Me"), fellow scatter Mel Torme, crooners Bing Crosby and Frank Sinatra, and one silly trio outing with Dinah Shore and opera star Joan Sutherland.

The fire of Fitzgerald's scat singing is also highlighted in an excerpt from "C Jam Blues," a legendary 1972 Jazz at the Philharmonic jam with the Count Basie Band (we only hear her head-to-head encounter with trombonist Al Grey). And there's a wonderful scene, shot at Ronnie Scott's jazz club in London, where a mischievous Fitzgerald delivers a faux country hoedown and some decidedly convincing soul grit that would have felt right on Stax Records.

One of the film's treats is hearing Fitzgerald's voice in a series of interviews. She didn't do many--again, that famous reserve--but she comes across as a warm, concerned and compassionate soul. Unfortunately, Fitzgerald was unlucky in love--a point Zwerin hammers home by following discussions of her failed marriages and relationships with appropriately melancholy songs ("Lover Man," "The Man I Love," "Something to Live For"). Similarly, the singer's devotion to children's charities is underscored by her rendition of the philanthropic anthem "For Once in My Life."

Zwerin was given exclusive access to Fitzgerald's estate, and, remembering that the singer was an intensely private person, one suspects a bit of sugarcoating in this first full-length portrait of the artist. The chronology is at times awkward and there's little from Fitzgerald's final decades--she died in 1996 after a lengthy illness.

On the other hand, there's an astounding continuity of spirit that belies more than five decades spent touring and performing. There was no diminution of craft, only constancy; perpetual youth in the voice, emotional connection in the lyrics, and, when needed, ineffable swing to lift spirits.

At one point, Fitzgerald and guitarist Joe Pass engage in a ruminative duet on "Once in a While." Charlotte Zwerin's delicate homage confirms that someone like Ella Fitzgerald comes along once in a lifetime.

CAPTION: After the decline of big bands, Ella Fitzgerald made an easy transition from swing to bebop.