The developer of the proposed 1,510-foot American Commerce Center has all but secured the zoning necessary to build the city's tallest structure at 18th and Arch Streets, tilting Center City's core westward.

City Council's Committee on Rules voted 9-0 yesterday to allow Hill International Real Estate Partners to blow past a current 125-foot height limit for that property to create a $1.1 billion, 63-floor office tower and 26-story hotel with a department store, a movie/dinner theater, and a supermarket at the base.

A full, final Council vote on the zoning could come as early as next Thursday.

The American Commerce Center would be one of the tallest buildings in the world and dwarf Philadelphia's highest skyscraper, the 975-foot Comcast Center, which sits across 18th Street on JFK Boulevard.

On its Web site, Hill International predicts that the American Commerce Center will do nothing less than "make Philadelphia the United States' newest epicenter of finance and innovation."

The project does not have an anchor tenant signed - critical for its viability - but Councilman Darrell L. Clarke, whose district encompasses the project, said he had spoken with prospective tenants.

"I think this is real," said Clarke, who declined to name the tenants.

Peter Kelsen, attorney for the developer, said that despite market conditions, "there is an ability and an optimism on the part of the owner-developer that they can move the project forward."

He pointed to the outlay of more than $2 million for planning and marketing as evidence of the developer's financial commitment and resources.

Council could approve the zoning next week - and it appears a majority of members supports the project. Kelsen said Hill International could submit a plan of development as soon as the spring, with groundbreaking possible late next year if the plans are approved by Council and the City Planning Commission. Completion would be in early 2013.

Prospective tenants represent a mix of existing Philadelphia businesses and new arrivals, Clarke said. He said his support for the American Commerce Center was based on the number of jobs that a building with nearly 1 million square feet of office space could attract.

"We have to take advantage of this in any economy, not to mention this economy," Clarke said.

Edward Panek, chairman of the Logan Square Neighborhood Association's zoning committee, urged Council to delay passage of the bill while the community negotiated with the developer.

Clarke said outstanding issues include traffic and the type of retail development. A supermarket, for instance, would involve truck traffic that requires loading and unloading, he said.

Residents of Kennedy House at 19th Street and JFK Boulevard, catercorner to the American Commerce Center site, oppose a project of such density on the half-block plot bounded by 18th, 19th, Arch and Cuthbert Streets.

Architect Gray Smith, hired by Kennedy House residents, said the current C-4 zoning limits established the neighborhood as a transitional area between high-rise Center City and low-rise residential communities.

"This property is on the edge of the business district, not the middle," Smith testified before Council.

Clarke disagreed. "The reality is this building is adjacent to the tallest building in Philadelphia," he said.

Architects John Partridge and Steven Henkelman, testifying separately, also rejected Smith's characterization. Henkelman compared the plan with "threshold" events, including the piercing of the William Penn height ceiling with the completion of One Liberty Place in 1987.

Partridge said that development along transit lines - part of the American Commerce Center project involves extending the Suburban Station concourse by two blocks - makes the site the "prime location" for such an ambitious building.

"This site is not the edge of anything," Partridge said. "This is the center of the main urban corridor in Philadelphia."

Contact staff writer Jeff Shields at 215-854-4565 or jshields@phillynews.com.