Nine years after the Barnes Foundation stunned the art world with a high-risk proposal to escape its litigious Merion neighbors by moving its renowned collection of Impressionist art to Philadelphia, it is getting ready to reveal its most closely guarded secret: what its new home will look like.

Foundation officials are scheduled to appear before the Philadelphia Art Commission at 9:30 a.m. Wednesday to seek conceptual approval for a new, larger gallery and classroom building on the Parkway between 20th and 21st Streets, the former site of the Youth Study Center.

The presentation to the commission, which has jurisdiction over the Parkway's appearance, is largely seen as a formality after years of pitched court battles with opponents of the relocation. Several key city officials already have reviewed the architectural design by the New York office of Tod Williams and Billie Tsien, and the commission is widely expected to sign off on the general massing and site plan.

The Wednesday hearing will effectively be a public coming-out for the long-awaited $200 million project.

In advance of the hearing, foundation officials submitted a packet of documents yesterday containing the site plan and various architectural drawings so commission members can have time to review the details. Ordinarily, such documents are also available to the public. But in an unusual move, Barnes officials asked the commission to consider the plans "proprietary" and withhold them from public scrutiny until Wednesday. A city solicitor approved the request.

Derek Gillman, the Barnes director, said the public would learn the details at the commission meeting, to be held in the city's public meeting room at 1515 Arch St.

"They'll learn what the site looks like, what the plan looks like, what the volume looks like, and how you go in and out of the site," he explained. "We'll see details of the amazing landscape."

Because the Barnes seeks only conceptual approval from the commission, it isn't obligated to make a full architectural presentation at this point.

"Of course, we think it is a wonderful building," Gillman said.

Still, the hearing could answer several important questions about the foundation's plans for its new Philadelphia operation. People in art and architectural circles have been especially keen to know how the designers would resolve the challenging problem of re-creating the Barnes' distinctive gallery experience in a modern building in an urban setting.

The sequence of the Barnes' Merion galleries and the arrangement for hanging the artwork have long been considered nearly as important as the artwork itself. They reflect the theories that the patent-medicine mogul Albert Barnes developed in the 1920s as he amassed the world's greatest assemblage of works by Cezanne, Matisse, and Renoir.

Barnes considered the "hang," as museum experts call it, so fundamental that he stipulated in his will establishing his foundation that the artwork could never be reorganized or moved. The foundation's battles with its Merion neighbors and the resulting financial insolvency caused the Barnes to reassess that clause.

When foundation officials petitioned Montgomery County Orphans Court in 2004 to break Barnes' will and move the collection to Philadelphia, they did, however, promise to replicate the Merion building's floor plan and the hanging scheme. As part of their plan, they also proposed to create a much larger museum building, with a gallery for special exhibitions, a cafe, bookstore, and auditorium.

Because the new Parkway building will be such a prominent cultural addition to Philadelphia, the Barnes has arranged for Williams and Tsien to present their design on Thursday to an invited group of about 350 local officials.

Contact architecture critic Inga Saffron at 215-854-2213 or isaffron@phillynews.com.