Leo Castelli, 91, the legendary art dealer who helped shift the focus of the early 1960s art world from Paris to New York by representing a new crop of painters, including Jasper Johns, Robert Rauschenberg and Andy Warhol, died Aug. 21 at his home here. The cause of death was not reported.

Mr. Castelli did not open his first U.S. art gallery until 1957, when he was almost 50 years old. But the impact he had on the art world internationally was profound, both because of the artists he represented and the manner in which he represented them.

He was born in Trieste, Italy, and received a law degree in Milan in 1924. He went to Paris in 1935 and went to work for a bank. He became involved in art and co-owned a gallery with his friend Rene Drouin on the Place Vendome. But the gallery opened just as World War II began and Mr. Castelli and his family headed to New York.

In 1943, the lawyer-turned-art-dealer enlisted in the U.S. Army and served in an intelligence unit, after which he was given U.S. citizenship. Not until 1957 did he open his first U.S. art gallery, after seeing work by two then-unknown painters, Rauschenberg and Johns.

Mr. Castelli was able to use his European background to convince collectors and dealers on that side of the Atlantic that the new American art was important. By 1964, the acceptance of the New York work became official when Rauschenberg became the first American to win the top painting award at the Venice Biennale.

In fostering the careers of such painters as Rauschenberg and Johns, admirers say he brought an energy and congeniality to the landscape of modern art he helped define.

Mr. Castelli's other artists included Frank Stella, Roy Lichtenstein, Claes Oldenburg, James Rosenquist, Robert Morris, Ellsworth Kelly, Kenneth Noland, Cy Twombly, Donald Judd, Dan Flavin, Bruce Nauman, Richard Serra and Andy Warhol.

"When I first saw the work of Johns and Stella, I was bowled over," Mr. Castelli said in 1984. "I just feel sheer, pure enthusiasm. And then you get feedback from a mysterious consensus out there that you are right. Then, of course, you intensify your push and drive."

Although some of his most famous artists defected to other dealers during the churning 1980s, Mr. Castelli's New York galleries were hothouses for major talents in the schools and styles that arose in postwar America and made New York the center of contemporary art.

He was in the forefront in promoting the successors to abstract expressionism -- pop artists, minimalists and conceptualists. During his rise to preeminence among dealers in the 1960s, he told an interviewer that he only followed where art led, not vice versa. "One has to accept what painters do. One does not have to like it, but one cannot discard it," he said.

"I've been learning from exhibitions at his gallery -- and from him -- for 30 years," Nan Rosenthal, 20th-century curator of the National Gallery in Washington, said a few years ago. "It's Leo's intelligence, and his loyalty to his artists, that makes him so extraordinary. It's not been about the business, but a passion for the art."