Anne d'Harnoncourt, 64, the formidable, high-spirited personification of the Philadelphia Museum of Art and an indefatigable advocate for the arts as central to the city's identity, died Sunday night.

She passed away at her Center City home after a undergoing a surgical procedure last week, said Art Museum chairman H.F. "Gerry" Lenfest. The Art Museum did not release a cause of death; there will be no autopsy, he said.

"It's a shock and it's very sad. It's unimaginable - the museum world without her," said Philippe de Montebello, director of the Metropolitan Museum of Art, a friend and colleague for decades. "There's no question that she was one of the very few people at the very summit to whom all museum directors and curators would look up and consult. She was a very big influence on the international museum group that meets every year. She was just someone who made a difference wherever she went."

In Philadelphia, she made a very big difference. Twinning partnership skills with the aristocratic Robert Montgomery Scott, the pair took a slouching institution with aged facilities and questionable relevance and parlayed it into one of the most vital comprehensive art museums in the country.

"She was our de facto cultural leader, our rock," said Gov. Rendell." She could always be counted on to lead the charge. She'll be missed in a thousand different ways."

She was largely responsible for launching the city's modern concept of cultural tourism with a blockbuster 1996 Cezanne retrospective that drew nearly 800,000 viewers - "a defining moment for the city," Rendell said. (Later she lamented the fact that after Cezanne, everyone expected her to produce an endless stream of hits.)

"Philadelphia has lost one of the greatest cultural leaders in its entire history," said David B. Brownlee, professor and chairman of art history at the University of Pennsylvania, in a prepared statement. "Anne d'Harnoncourt transformed the Philadelphia Museum of Art in a way that modeled and contributed to the transformation of the city of Philadelphia. She attracted the best and brightest curators in the world, created with them an ideal collegial environment in which to work and charged them with the task of creating exhibitions and other programs that would change the city and speak to the world."

Word of her death stunned the arts and business community. She was recently working as usual and attending parties. Today she had been expected to meet with colleagues at the Association of Art Museum Directors gathering in Michigan.

"She called me and left me a message [Sunday] and said the operation had been a success," said Lenfest. "The next thing I know I got a call that she died."

Though Miss d'Harnoncourt - who came to the museum in 1967 and became curator of 20th century art in 1972 - was director starting in 1982, her career in the museum was in many ways coming into its prime.

She was in the midst of overseeing a massive $590 million expansion and renovation of the museum, including a Frank Gehry reworking of the main building, restoration of the exterior and the erection of a new sculpture garden atop a parking garage. In November she cut the ribbon on the Perelman annex, captured space in a former insurance building the museum remade into galleries and offices.

Lenfest said he met with Art Museum employees yesterday, and told them that the work will continue. "That's what Anne would have expected - for us all to hold hands and go forward." One employee sang "Amazing Grace."

Lenfest said he had been planning to step down in October, but now will stay on until after a new director is chosen. At that point, a new chairman will be elected.

"I think the new chairman will have to have good chemistry with the new director," he said, noting that chief operating officer Gail M. Harrity will continue in place.

Most recently she had landed the Art Museum an enviable spot at the Venice Biennale curating the American Pavilion with a major Bruce Nauman show, and engineered the sale of a prized Thomas Eakins owned by the museum to help the city keep a more prized one, his iconic The Gross Clinic.

A tall, handsome woman with a viola-like vocal range, Miss d'Harnoncourt was born Sept. 7, 1943, in Washington, D.C., a scion of an illustrious arts family that included a cousin from the Austrian side of the family, famed conductor Nikolas Harnoncourt, whom she called "Cousin Niky." She grew up an only child in Manhattan, where her father, René d'Harnoncourt, a painter and expert in both Mexican and American Indian art, was director of the Museum of Modern Art.

She attended the exclusive Brearley School, and at Radcliffe, majored in history and literature of Europe and England since 1740. While earning a master's from the Courtauld Institute of Art, London University - with a thesis on moral subject matter in mid-19th-century British painting with special emphasis on the Pre-Raphaelites - she worked at the Tate Gallery.

She was an assistant at the Philadelphia Museum of Art for two years, from 1967-69, and then left to become assistant curator of 20th art at the Art Institute of Chicago.

She then returned to Philadelphia in 1969, as curator of 20th century art, and stayed. Duchamp was a leitmotif in her tenure, and was often the lens through which she saw all other artists. But her interests as curator extended to areas as divergent as Violet Oakley, Jasper Johns, Dan Flavin, Frank Stella and John Cage, and as director was an advocate for Asian art, arms and armor, fashion and industrial design.

During her tenure, her staff produced major retrospectives on Brancusi, Barnett Newman and Dalí, as well as surveys on the Pennsylvania Germans and 18th century Rome.

As a colleague, she was unusually supportive - and could be a very controlling presence.

"She was brilliant and a perfectionist," said Sandra A. Horrocks, a public-relations and fund-raising executive who worked with Miss d'Harnoncourt for three decades, "From focusing on word choices in documents to how merchandise was displayed in the museum store to the color of the walls in an exhibition - nothing escaped her discerning eye."

Among her most ambitious achievements were the reinstallation of the European collections in more than 90 galleries, and, a few years later, renovation of 20 galleries of modern and contemporary art.

Her track record, pedigree and easy way with donors were lure to other museums looking for leadership. Her name was often bandied about in the press as a candidate for jobs, but the Met's Montebello said if the Met had offered her his job (he is stepping down), she would have declined.

"She had built that museum on the strengths of what Fiske Kimball had done. I don't think she would have taken the job. She was committed to Philadelphia."

And that, in turn, sent a message, said Rendell.

"The fact that she chose to stay here in Philadelphia was one of the reasons the art museum board did everything they've done in the last decade," he said. "It was a signal to all of us that we are a first-class arts and culture community.

She is survived by her husband, Joseph J. Rishel, a senior curator at the museum. Services are private. A public memorial will be schedule for a later date.

Donations in her memory may be made to the Philadelphia Museum of Art, P.O. Box 7646, Philadelphia, Pa., 19101-7646.

Contact culture writer Peter Dobrin at 215-854-5611 or pdobrin@phillynews.com. Read his blog at http://go.philly.com/artswatch.