Jo Stafford, a singer who was a favorite of soldiers during World War II and whose recordings made the pop music charts dozens of times in the 1950s, died Sunday of congestive heart failure at her home here. She was 90.

According to her son, Tim Weston, she had been in ill health since October and had been hospitalized several times since 2002.

Stafford had a long career but enjoyed most of her success from the late 1930s to the early '60s. Her skills were apparent from the beginning, when she sang as a teenager in a vocal trio with her two older sisters, Pauline and Christine.

"Mom graduated from high school on a Friday and was doing soundtracks at RKO on Monday," her son said.

Qualities that were present at that time became the foundation of her vocal style: her impressive technical skills, flawless intonation and cool but expressive tone. Whether Stafford was singing romantic numbers such as "You Belong To Me" -- a No. 1 hit in 1952 -- or making duets with Frankie Laine on the lighthearted, comedic "Hambone" (a No. 5 hit the same year), her performances were superb displays of crystal-clear musicality combined with an insightful understanding of lyrics.

Those skills were particularly useful early in her career, first when she was singing lead in the trio with her sisters, then during her work with the Pied Pipers. Initially an octet, with seven male singers and Stafford, it was pared to a quartet when the group began working with the Tommy Dorsey Orchestra in 1939. Stafford's impeccable lead voice can be heard in the backing for Frank Sinatra's No. 1 hit "I'll Never Smile Again," as well as the Connie Haines hit "Oh Look At Me Now."

Stafford's solo career began with an inextricable link to the war. A favorite of American soldiers, she was told by a veteran of the Pacific that "the Japanese used to play your records on loudspeakers across from our foxholes so that we'd get homesick and surrender." Not surprisingly, servicemen affectionately referred to her as "GI Jo."

Stafford and her second husband, pianist/composer Paul Weston, were viewed by most of their contemporaries as musical class acts who brought clarity, focus and sophistication to the most lighthearted pop music. Which made their transformation into Jonathan and Darlene Edwards -- a duo that was the surprising last highlight of Stafford's career -- such a remarkable accomplishment.

The premise was simple enough: They would do imitations of a minimally skilled duet of singer and piano player -- the sort who can frequently be heard in no-cover-charge cocktail lounges everywhere. But as interpreted by Stafford's pliable voice, the songs came out just a little sharp in one spot, a bit flat in another, with the rhythm slipping from beat to beat.

Did Stafford find it difficult to sing in such ear-jarring fashion? "Well, Jo Stafford might have found it difficult," she told the Chicago Tribune in 1988, "but Darlene had no problem at all."

It worked so well, in fact, that the duo's recording of "Jonathan and Darlene Edwards in Paris" won the Grammy for Best Comedy Album of 1960. It was the only Grammy that Stafford would win.

Jo Elizabeth Stafford was born Nov. 12, 1917, in the San Joaquin Valley town of Coalinga. Her parents, Grover Cleveland Stafford and Anna York Stafford, moved the family to Long Beach, where she graduated from high school after having five years of classical voice training. Besides her singing, she was, according to her son, a very good pianist.

After working for the Dorsey Orchestra from 1939 to 1942, Stafford began her solo career as one of the first acts on the new Capitol Records label. She moved to Columbia Records in 1950 and back to Capitol in 1961. Although she was active for a relatively brief time as a solo artist, she sold more than 25 million records.

Once she had decided to end her singing career in the mid-1960s, however, Stafford seemed little tempted to return. Asked at the time whether she might consider the sort of comeback that had worked for such contemporaries as Rosemary Clooney and Patti Page, her response was to the point. She no longer sang, she said, "for the same reason that Lana Turner is not posing in bathing suits anymore."

Stafford did make a few appearances after the 1960s, among them a revival of Jonathan and Darlene Edwards in the late '70s for which she sang inimitable lounge versions of the Bee Gees' "Stayin' Alive" and Helen Reddy's "I Am Woman."

Stafford's first marriage -- to Pied Pipers singer John Huddleston -- ended in divorce. She married Weston in 1952; they had two children, Tim, a musician and record producer, and Amy, a singer. Her husband died in 1996.

She is survived by her children; four grandchildren; and her younger sister, Betty Jane.