Atlanta Mayor Kasim Reed on Tuesday urged voters to shake off doubters and discouraging polls recently offered up by news outlets, and vowed his own “all-out” support of a 1 percent regionwide sales tax to pay for transportation projects.

In a fiery speech that compared the referendum to Atlanta’s history of tackling game-changing projects — including MARTA, Ga. 400 and the 1996 Summer Olympics — Reed vowed that he would become the confident but urgent voice for the T-SPLOST campaign that it has so far lacked.

“Take it from somebody who knows how to win,” Reed told a City Hall crowd, reminding them of his 700-vote victory in 2009. “You have to excuse me for not being nervous when it says we’re behind. It was always going to be close.”

Reed’s full-throated declaration that the Atlanta region desperately needs the T-SPLOST to remain a hub of the Southeast stands in contrast to a variety of opponents on both the right and left. Some of those oppose the addition of another tax or say it won’t solve the region’s traffic problems; others believe it concentrates too much on roads at the expense of transit.

The vehemence of Reed’s advocacy also contrasts with that of many of his political allies, who have occasionally hedged their support. Gov. Nathan Deal, for example, often prefaces his words of support with the fact that the local referendum drive started before he became governor. A few elected officials who once backed the effort have now come out against it.

“You’re going to continue to see elected officials do what elected officials do — move away from something that is about to fail,” Reed said after his speech in an exclusive interview with The Atlanta Journal-Constitution. “But this matter is too important. This is our generation’s moment to really move this region and this state ahead.”

Much of Tuesday’s effort was aimed at African-American Democrats who could offset opposition in metro Atlanta’s predominantly Republican suburbs. But Reed also used language aimed at younger voters less inclined to identify themselves by race or geography, saying that the T-SPLOST would be Atlanta’s latest bid to reach across vast divides in the name of economic development.

“We did what you asked us to do,” he said of the list of projects assembled by a regional roundtable. “You all said you were sick of partisanship, and we did this in a bipartisan way. You all say you were sick about black folks being against white folks — we did it in a biracial way. You all said you were sick of rural against urban — we did it with rural and urban.”

The tax could raise $7.2 billion over a decade for a range of projects from rail lines and interchanges to sidewalks and pedestrian crossings. But the referendum has been attacked by an assortment of foes. Some are tea party members who dislike the possibility of a regionwide tax. Others are advocates of transit who say the project list skews too heavily toward roads. Still others distrust state and local transportation officials because of the continued existence of the Ga. 400 toll, despite promises that it would end.

On Tuesday, state Sen. Vincent Fort and John Evans, president of the NAACP’s DeKalb County branch, said the T-SPLOST should be voted down. Guarantees by state and local agencies to include small minority contractors are flimsy, they said.

Fort said the “good ol’ boy” system of doing business is alive and well in Georgia, citing a study this year that showed that African-American companies won 1.1 percent of contracts from the Georgia Department of Transportation.

“Don’t be tricked by the hype,” he said. “Get back to the table and do it the right way. You know what happens: Three or four companies get all the business.”

Some polls have shown the T-SPLOST losing ground over time and now facing defeat.

Last week a Rosetta Stone Communications poll conducted for Channel 2 Action News found 33 percent of voters in the 10 counties in the Atlanta region in support of the proposed tax, while 56 percent opposed the plan. In June, the same poll found 38 percent of voters support the proposed tax, while 49 percent oppose the plan. A similar poll in May had the numbers more evenly split at 42 percent supporting and 45 percent opposed.

But Reed touted a poll of 800 metro Atlantans commissioned by the pro-tax “Untie Atlanta” campaign that showed 41 percent opposed and 38 percent in support — a statistical tie after figuring in the 3 percent margin of error.

On Tuesday, Reed pleaded for help from the overwhelmingly African-American crowd, citing a double-digit jobless rate among black residents. He said the T-SPLOST needs the support of minority business people in Atlanta and Fulton and DeKalb counties, which have promised to incorporate small, minority and women-owned firms in their procurements. He urged the crowd to text, tweet, email and call friends and publicize their support on Facebook.

“I need you all to fight for this thing,” he said.

Desiree Pedescleaux, an associate professor of political science at Spelman College, said Reed’s vigorous support “does make a big difference.”

“But the big unknown is really getting folks to the polls,” she said. “July is always a sleeper election. Just lighting a fire under folks and getting them to the polls is going to be the challenge.”

The pro-tax campaign has the support of much of Atlanta’s business community. The T-SPLOST, as the tax is often called, got a late but potentially important new backer this week in the Atlanta Business League, a 79-year-old organization that represents a who’s who of minority businesses.

The organization decided it was time to take a stand and support a revenue stream that could help reduce unemployment in the African-American community, Chairman Thomas Dortch Jr. said.

“We’re going to be in a sprint to the finish line,” he said. “You’re either all in or you’re all out.”

For Field Searcy of east Cobb, the race is still too close for comfort. He is campaigning against the tax, partly because he doesn’t believe it would solve congestion.

“We’re certainly not going to let up on what we’re doing,” he said. “We’re going to keep pushing harder and harder. I don’t know how it’s going to go. [Reed] is right — it could be won by one vote.”