A coalition of affordable housing and smart-growth advocates has fired back at a Fairfax County supervisor who says subsidized housing in Tysons Corner will cost about $500 million.

The group accused Supervisor Pat Herrity (R-Springfield) on Friday of relying on “faulty calculations” and “misrepresentation” for what Herrity claimed was the first estimate of the real cost to set aside workforce housing in Tysons Corner. The group also challenged Herrity’s claim that most of the subsidized workforce housing will go to households earning more than $70,000 a year and as much as $120,000 a year.

Leaders of the Northern Virginia Housing Alliance, AHOME, and the Coalition for Smarter Growth reaffirmed their support for the affordable housing and planning initiatives developed by the Democratic-led Board of Supervisors as the best way to ensure that people of all classes will have available housing in Tysons Corner as the suburban crossroads becomes an urban center.

“To be clear, Fairfax County and its taxpayers are not providing $500 million worth of subsidy in cash or otherwise for workforce housing at Tysons Corner,” the coalition said in a written statement Friday. “Affordable housing is one of the community needs being provided by the private sector as part of a comprehensive plan that allows those developers significant additional development. It is priced into what the developers pay for the land and into the deals that they structure as they redevelop their properties.”

The rebuttal to Herrity’s cost estimate came from Michelle Krocker, executive director of the Northern Virginia Housing Alliance; Paul Browne, president of AHOME, a group of businesses, developers and service groups; and Stewart Schwartz, executive director the Coalition for Smarter Growth.

“Households at many income levels are facing affordability problems in Fairfax County, even when they have two income earners,” the trio said. “So the plan’s provisions, which ensure a range of housing affordability within Tysons Corner, are essential. At a time when companies in Tysons Corner are having trouble attracting lower-wage workers because of the lack of nearby affordable housing and long commutes, providing more affordable housing within Tysons Corner is a win-win solution.”

The coalition also argued that creating affordable housing is also a way to alleviate transportation problems because it enables workers to live close to their jobs. “Similarly, transportation demand management programs (TDM), which were also criticized in the article, are in actuality a proven means to increase carpooling, transit, walking and biking, reducing the number of cars traveling during peak commuting hours,” the group wrote.

On Wednesday, Herrity reignited debate over an issue that has smoldered for years. Having grown impatient with efforts to pin down the costs from staff, Herrity said he and his staff gathered enough data on their own to create estimates based on public documents and testimony from a developer that he said show the county will direct more than $2.2 billion extracted from developers to what he deems are nonessential initiatives such as green buildings and traffic-management plans. At the same time, the county has failed to identify where it will find the $1.8 billion needed to build transportation infrastructure in Tysons, Herrity said. He said he worries that taxpayers and businesses will ultimately foot the bill.

“The back of the envelope is better than a head in the sand,” Herrity said in response to earlier criticism.