FORT WORTH -- Ruth Carter Stevenson, who stepped out of the shadow of her legendary Fort Worth father, Amon Carter Sr., to become a national figure in the American art world, died Sunday night at her home.She was 89.Under Mrs. Stevenson's long leadership, the Amon Carter Museum went through major expansions and acquired a collection of American art considered one of the finest anywhere.Mrs. Stevenson, the youngest of Amon Carter's Sr.'s two children, was born on October 19, 1923, the same year her father took over as publisher of the Fort Worth Star-Telegram. Carter was also an oilman, philanthropist, friend to American presidents and national celebrities, and a voracious collector of Western paintings and sculptures, mostly by Charles Russell and Frederic Remington.By the time of Carter's death in 1955, his collection had grown to about 400 pieces. It was left to Mrs. Stevenson by her older brother to carry out a key provision of her father's will, building a Fort Worth art museum to house the collection. Collaborating with famed architect Philip Johnson, Mrs. Stevenson presided over the opening of the Amon Carter Museum in 1961.In the years that followed, Mrs. Stevenson, as president of the museum's board, demonstrated her father's fierce will and insistence on quality. She also discovered and refined her own eye for great art. Within a few years of the museum's opening, Stevenson and the Fort Worth museum had pushed far beyond Amon Carter Sr.'s Western aesthetic, buying paintings and art objects across a broad spectrum.In the process, Mrs. Stevenson herself became a fixture on the American art scene. She was a close friend of Georgia O'Keeffe until the artist's death in 1986. In 1979, she became the first female board member of the National Gallery of Art in Washington, D.C., and later the first woman to become the board's chairman."It's a great institution because of her," Earl A. Powell III, director of the National Gallery and a longtime friend, said of the Amon Carter Museum. "Over its history the Carter has put together one of the great collections of American art.... It's a great, great place she has created for Fort Worth and the nation."Michael Conforti, director of the Clark Art Institute in Williamstown, Mass., was among high-profile museum leaders whom Stevenson recruited to serve on the Carter museum board."She has so many people who admire her so deeply, so that when she calls on them for something, they'll do it," said Conforti, a former president of the American Association of Art Museum Directors. "She has taken her father's legacy and given it a vision that he would only applaud, though she moved it in a different direction."The Amon Carter now has one of the great collections of American painting, to the degree that the Kimbell [Museum of Fort Worth] has one of the great collections of European paintings."