DeKalb County politicians, activists and residents have united to fight a proposed penny sales tax for regional transportation plans unless the final project list gets trains running in south DeKalb.

So far, the 5.4-mile rail line to link the Indian Creek MARTA station to Wesley Chapel Road, known as the I-20 project, isn’t a transit priority for the roundtable executive committee that is recommending projects.

DeKalb leaders held a news conference before the committee’s meeting Tuesday to urge the I-20 project be added -- or else.

“If we do not have that rail, we cannot support the penny,” said Larry Johnson, the DeKalb County Commission’s presiding officer.

Voters in 10 metro Atlanta counties will decide next year whether to approve the 1-cent sales tax to pay for a $6.1 billion list of projects of regional significance.

Already there has been debate about how much the executive committee, made up of mayors and county commissioners, should set aside for roadwork versus transit.

DeKalb has traditionally supported transit. For 30 years, its residents and those in Atlanta and Fulton County have paid an extra 1-cent sales tax to fund MARTA.

That disparity already has prompted threats from mayors in DeKalb and Fulton, that they won’t support the 2012 vote unless other counties chip in for a new regional transit system.

Conventional wisdom holds that without the two urban counties’ support, the referendum will most likely fail.

“Transit addresses traffic and belongs where there is the greatest concentration of people,” DeKalb CEO Burrell Ellis said.

DeKalb is not without rail projects. A proposed line to connect train stations at Decatur and Lindbergh, known as the Clifton Corridor, is already included on roundtable priorities.

County leaders say they support both new rail lines. Indeed, the I-20 project has garnered support around DeKalb.

“To think that DeKalb would be ignored after being a leader in this kind of transit investment, it’s inconceivable,” said Commissioner Elaine Boyer, who represents the northern part of the county.

The I-20 rail extension would cost an estimated $522 million and take about six years to complete. Advocates hope the relatively short timeline will boost the project's chances of making the executive committee's final cut for a draft list by Aug. 15. The final project list will be approved by Oct. 15.

They also hope to bolster their case by reaching out to other southside counties, to show the need for rail to be extended in that direction.

In the end, though, leaders said it may come down to continually making the point that the project is key to capture DeKalb’s support.

“Without the I-20 rail, this referendum has no chance of getting more than a quarter of the votes in DeKalb County,” said David Schutten, president of the Organization of DeKalb Educators. “It’s that simple.”