The American Commerce Center, a 1,510-foot skyscraper proposed for 18th and Arch streets, cleared its first hurdle yesterday when the City Planning Commission signed off on legislation for necessary zoning changes.

The developer, Hill International Real Estate Partners, now faces a City Council hearing in two weeks. Council could give the legislation final approval by Dec. 11.

But will the skyscraper be built in an economy in which soaring costs for construction materials were followed by a collapse in the financing markets necessary to build big-ticket developments?

Garrett Miller, Hill's president, said the skyscraper was in the first year of what is likely to be a six- to eight-year process.

He said he hopes the credit markets will be rebounding later in that cycle.

"There are hundreds, maybe thousands of variables in developments," Miller said.

"It's no different with this one."

Yesterday's three-hour hearing stuck closely to a story line aired when the Planning Commission first considered the zoning issues in mid-July.

That set off a generational split, with younger residents of Center City urging approval of the building while older residents who live in high-rises just south of the skyscraper site opposing its size and scale.

With a 1.5-acre site on half of a city block, the developer needs zoning changes to build anything taller than 125 feet and to allow for dense development in a relatively small footprint.

Joseph Beller, an attorney for nearby Kennedy House residents, said the skyscraper could be a "wonderful building" somewhere else. Beller complained that the city is giving the nod to projects in "piecemeal" fashion rather than following a larger plan.

"That's exactly what you shouldn't be doing with city planning," Beller said.

"If you find a place where it fits, it would be the greatest thing in this city."

Sarah Maloney, one of several young professionals to praise the project, said the potential building amenities reminded her of a neighborhood where she previously lived in Boston.

"I think Logan Square has the ability to be that kind of place," she added.

The project, with a 1,210-foot office tower topped with a 300-foot spire and a 477-foot adjacent hotel attached by a sky bridge over a public plaza, would be 50 percent taller than the 975-foot Comcast Center, one block to the east.

It would be the tallest building in the city.

Larger projects are planned in Chicago and New York City.

"It's going to end up as the third-tallest building in America, eventually," architect Gene Kohn said.

Andrew Altman, the city's commerce director and deputy mayor for planning and economic development, framed the first step for the skyscraper as a question on whether that type of dense development was appropriate for 18th and Arch streets. Altman, also chairman of the Planning Commission, concluded that it was appropriate but that the developers will have to come back for approval of their building plan if Council passes the zoning bills. *