Representatives of a variety of local environmental, biking, transit and park advocacy groups appeared at a downtown Atlanta training center on Wednesday morning to proclaim their support for Tuesday's regional transportation referendum.

With the campaign coming down to the wire, advocates of the 1 percent sales tax say they need the energy and enthusiasm of environmental activists.

"Even when you're preaching to the choir, the choir needs to be warmed up," Atlanta Mayor Kasim Reed said at the Southface Eco-Office.

The groups were assembled to help blunt the impact of the Georgia Sierra Club's opposition to the 1 percent sales tax, commonly called the T-SPLOST, which would raise about $7.2 billion over a decade for transportation projects in the 10-county metro Atlanta region.

The Sierra Club argues that the project list leans too heavily toward building roads at the expense of public transit, and should be scrapped and redone.

Reed said that was unrealistic.

"The Sierra Club should realize they are not in California; they're in Georgia," Reed said. "The people who are going to get credit if we fail are against more transit, not for it. I've been stunned by this notion that losing will produce a better result."

The Sierra Club has about 10,000 dues-paying members in Georgia, with roughly half of them in the 10-county metro area. The organization polled its members before coming out against the T-SPLOST earlier this year, arguing that transportation agencies need to be more transparent and accountable and that public transit should get more support.

"Reasonable people can disagree," said Colleen Kiernan, director of the Sierra Club's Georgia chapter.

On Wednesday, several pro-tax groups said they could contribute volunteers to knock on doors and man the phones. Together, the 20 groups — including The Southern Environmental Law Center and The Atlanta Bicycle Coalition — have more than 5,000 members and email lists with thousands more.

Another group key to the tax vote, African Americans, heard heated appeals from both sides of the debate Wednesday. Reed appeared on radio station V-103 to defend the plan to the its heavily black audience. Shortly before Reed's appearance, John Evans, president of the DeKalb County NAACP urged listeners to reject a transportation plan he says inadequately expands rail.

"The NAACP's reason for not wanting it is, they have been promising us rail for 20 years, and have not paid the price to do it," Evans said.

Reed, pointing to $600 million earmarked to MARTA, said the plan pays for rail and is critical to economic development.

"I don't know how he [Evans] believes that $600 million is a small amount of money," Reed said. "It's the biggest investment in MARTA that MARTA has had in 20 years that's not from the federal government."

Reed will get a key ally next week in making the case that the tax vote is critical to economic development. Gov. Nathan Deal will join Reed at a Monday news conference, their first joint media appearance touting the transportation tax.

Staff Writer Jim Galloway contributed to this report.