The development group that wants to build a 6,000-seat velodrome for bicycle racing in South Philadelphia's FDR Park unveiled its proposal Wednesday evening - the first lap in a long campaign to win permission for the private arena.

More than 150 people packed into the meeting of the Parks and Recreation Commission at the American Swedish Historical Museum to hear the presentation. The crowd seemed about evenly split between neighborhood residents and bicycling enthusiasts from around the city. Because the $100 million, for-profit velodrome would displace about four acres of the park along Broad Street, the commission must determine whether it meets the conditions set out in the city's Open Lands Protection law.

Although the velodrome developers have promised to make significant park improvements to mitigate the arena's impact, several neighborhood residents expressed skepticism about the benefits of another large facility in South Philadelphia. The velodrome would be located across from the sports complex and a few blocks from the site of a newly approved casino on Packer Avenue.

"This is the elephant in the room. We are already impacted so severely," argued Anna Maria Vona, who uses the park for morning walks. "I'm tired of outsiders coming into our community."

The project's backers, led by Philip J. Senechal, an executive at a private equity firm, countered that the velodrome would be more like a rec center than a sports complex-style arena. It would offer recreational activities for residents, as well as cycling programs tailored to low-income schoolchildren from around the city. They are offering free space to Cadence Youth Cycling, which provides racing and leadership training.

"If you have a facility like this, you'll have thousands of kids graduating high school and going off to college," promised Ryan Oelkers, a cofounder of Cadence.

But even some bicyclist enthusiasts complained that it was wrong to locate the velodrome on parkland. "It's the right idea, wrong location," said one speaker, who urged the group to look for another site.

The commission took no action Wednesday. Before the project can be approved, it must be vetted by the city's art and historical commissions, the National Park Service, and state agencies.