Is Center City Philadelphia ready to take on a ... SUPER SKYSCRAPER

So, would it be cool to have a super-tall skyscraper - the fourth-tallest building in the nation - in the heart of downtown Philadelphia? How likely is it to happen?

The developers spent $30 million to acquire the land, a parking lot, at 18th and Arch Streets. Design plans are in hand; there appears to be some political support. The owners have begun discussions with potential tenants for the American Commerce Center, a block from the new Comcast Center.

At 1,510 feet, it would be dramatically taller than the just-completed Comcast building, the city's current tallest building at 975 feet.

Philadelphia City Councilman Darrell L. Clarke recently introduced a measure that would lift the height limit at the site to accommodate an office tower spire, with 63 floors, a 320-room hotel, a movie theater and retail shops. Mayor Nutter favors the project.

But there are many "ifs" - ranging from zoning to attracting a major tenant. Developers Joseph Grasso and Garrett Miller of Walnut Street Capital L.L.C., a Philadelphia firm, acknowledge that everything is preliminary.

"The best-case scenario is 36 months out to begin construction," Grasso said.

If built, the $1 billion, 2.2-million-square-foot skyscraper - taller than the Empire State Building - would rank fourth behind Chicago's current tallest, Sears Tower (1,730 feet with antenna), the Chicago Spire (2,000 feet) under construction, and New York's coming Freedom Tower (1,776 feet).

Here's the outlook for Philadelphia's tallest building's getting off the ground:

FIVE REASONS IT WILL HAPPEN

1. The city is on a roll. More young professionals are choosing to live in the city. The Comcast Center shows it can be done. BlackRock Inc., a global investment-management and advisory company, is seriously eyeing Philadelphia because of the new Cira building proposed for the 30th Street Station area.

The 18th and Arch site is the "last remaining large office site" in the West Market Street corridor, said Paul Levy, executive director of the Central Philadelphia Development Corp. "It's unencumbered, easy to build on," and zoning would permit a large office and retail building.

2. Center City office space is tight. There is a "need for large blocks of office space for growth," said George Cauffman, senior vice president and leasing agent at CB Richard Ellis Group Inc. Rents in Philadelphia remain a bargain compared with Washington, Boston and New York. The high-technology and environmentally "green" building could entice out-of-towners and suburban businesses. Center City's office-vacancy rate, now about 8.9 percent, is expected to drop below 8 percent by the end of the year.

3. The project is supported by pro-growth and development-friendly Nutter, who signaled that he intended to be a devotee of smart urban design by recharging the ignored-for-the-ages City Planning Commission.

4. Soaring gasoline prices favor urban development. Situated in the heart of a lucrative metro region, blessed with its transit system and regional highway network, the site is accessible to a three-state workforce. Major employers considering Blue Bell or Exton might find strategic advantages to being downtown. Stories about the death of the suburbs are already appearing in the national press.

5. A psychology that bigger is better, and tall impressive buildings create momentum. A view that if the city wants to move forward and continue to grow, it must build super-tall towers. The no-higher-than-Billy Penn's-hat thing is a distant memory.

FIVE REASONS IT WON'T HAPPEN

1. Failure to secure an anchor tenant. In the 1980s, buildings went up speculatively, and developers got financing and built without lead tenants in place. "That really doesn't happen anymore," said John Grady, senior vice president at Philadelphia Industrial Development Corp., a quasi-public city agency. Probably 60 percent of the new building might have to be pre-leased to secure financing. Can the developers find a (major) tenant to pay a rent - probably $40 to $50 per square foot - to support construction costs and allow them to secure financing? "That's the fundamental issue with any development project," Grady said.

2. The existing Philadelphia tax structure and business-privilege tax - without extending tax breaks - discourage new businesses. "The business-privilege tax is a very confusing tax; it's onerous," developer Miller said. "I don't think you can flat-out abolish it, but you can take an incremental approach. All net new jobs and anybody coming into the city creating new jobs would not pay the BPT, but would pay wage taxes."

3. Bad loans have created a banking crisis. "This is a very, very challenging time with regard to the lending institutions," Grasso said. "But if we land the right tenant, we believe we will be able to get the right kind of financing. There is certainly money out there for the right kind of deals."

4. There will be skepticism about the development team, which hasn't done a construction project of this magnitude before.

Cauffman, of CB Richard Ellis, said the developers, including private-equity partner Multi-Employer Property Trust, are "a solid ownership entity" and "very forward-thinking. They have surprised people. They went out and bought this piece of ground - it's a great piece. They are doing all the right things."

5. Residents' objections or city planning concerns about the design and density could hurt. Neighbors have questions about the traffic, congestion and crowds the building will draw. Others wonder how such a tall building may obscure light and views. If the shadows go all the way to Logan Square and the fountains, what does that do to the character of the neighborhood?

"We expect to have meetings through the summer on these nitty-gritty issues," said Rob Stuart, president of the Logan Square Neighborhood Association. "Can the neighborhood absorb something as big as the original World Trade Center? This is by no means a done deal."