TAMPA — The debate about a proposed high-rise apartment tower near the Hillsborough River increasingly is returning to one question:At 36 stories, would the Residences at the Riverwalk be too massive for Tampa's arts district?Both sides on the issue spoke Monday at a meeting of trustees for the David A. Straz Jr. Center for the Performing Arts."This building is too big … is just not suitable," said trustee Don E. Jones Jr., one of several to say the tower would be out of scale next to the Straz Center, John F. Germany Public Library and Tampa Museum of Art.Another concern for them was the tower's impact on traffic.But trustee Frank Morsani said that "this is a step forward" and predicted the project would help the evolution of downtown."If we put this building here, more people will put their buildings someplace else in the future," he said.In a sign of how important the project is to him, Tampa Mayor Bob Buckhorn went to Monday's meeting to appeal to Straz Center trustees.At stake, Buckhorn said, is Tampa's ability to appeal to bright, young professionals who now leave for cities like Austin, Texas, and Raleigh-Durham in North Carolina."The demand for residential living in downtown Tampa by these young people is going to drive the economy for the next 20 years," he said. "This is about changing our economic DNA and creating an environment where these people want to be."Buckhorn said he understands concerns about the project's size, but thinks the "pedestrian experience," not the tower's height, will be key in how people feel about it.That's because, he said, pedestrians don't walk around with their heads tilted back, looking at the tops of buildings. More important, he said, will be what people see at street level.Along with 380 apartments and a 620-space parking garage, the tower would have 10,000 square feet of ground-floor shops and restaurants."This is not going to block the waterfront," Buckhorn said, turning to another criticism.The Straz Center sits 67 feet from the river, he said. The Tampa Museum of Art is 127 feet from the river. At its closest, Buckhorn said, the tower would be more than 200 feet from the river.As for traffic, Buckhorn said, selling city land to the developers will provide the money to rework the street grid, making it safer.Developer Phillip A. Smith said the tower is estimated to generate five more trips per hour. Once Cass and Tyler streets are made into two-way streets, he said, a lot of westbound traffic now on Tyler will go to Cass, making Tyler less busy and more of a "red-carpet entrance to the Straz."Besides the tower's scale and traffic, other issues did not get as much attention Monday.Buckhorn said that's a testament to the work Smith and his business partner Greg Minder have done addressing concerns of their neighbors. In recent weeks, they have agreed to:• Delay construction until May to avoid disrupting the Straz Center's critically important Broadway series.• Provide business interruption insurance in case construction does hurt the Straz Center.• Maintain an elevated pedestrian bridge from the William F. Poe Parking Garage to the library and the Straz Center.Developers also have offered to the Straz Center an unrestricted $1 million gift.Trustees did not take a formal position, but the center is surveying both them and directors of its charitable foundation on whether they favor the tower at its proposed site, an acre behind the library's annex and in front of the Straz Center's arrival plaza.Survey results will go to the City Council, which is scheduled to vote on the project Aug. 8.