Transit advocates aren't happy with a suggestion to cut the first leg of an Atlanta-to-Macon rail line out of the project list for next year's transportation sales tax referendum.

With less than a month to go before a roundtable of mayors and county commissioners takes its first crack at paring a wish list for the 10-county Atlanta region, the Fair Share for Transit campaign has asked metro leaders to rethink leaving out both the commuter rail line through Clayton County, envisioned as eventually linking to Macon, and a light-rail light reaching Gwinnett Place.

Neither project made the "first pass" list produced two weeks ago by the Atlanta Regional Commission, the region's official planning agency, which whittled the full $22.9 billion wish list down to $12.2 billion as a starting point. The final list of regional projects will total $6.1 billion.

The ARC list broke down funding at 55 percent for roadwork and 45 percent for transit.

But Fair Share on Monday asked that $4 billion, or 66 percent of the funds expected to be generated by the tax for regional needs, be set aside for transit.

Norcross Mayor Bucky Johnson, the roundtable's chairman, said it is targeting 40 percent to 60 percent for transit.

"This is not a transit tax, this is a transportation tax," he said. "We give [the group's suggestions] weight, but it has to be weight that fits in with everything else we've heard."

But Fair Share, a group of about 75 businesses and nonprofits put together by the Livable Communities Coalition, believes the sales tax will give the region its best shot at building a metrowide transit system. The lack of such a system threatens Atlanta's potential to become a top-echelon economic center, said Ray Christman, the coalition's director. Studies show road building and widening projects do less to solve congestion because cars quickly fill the new lanes.

Fair Share produced a menu of transit proposals that it wants given priority in making the final list. In the $4 billion, the group wants about $1.2 billion set aside for bus services, MARTA system improvements, pedestrian and bike projects, the new Multi-Modal Passenger Terminal, and other items. It then wants an additional $2.8 billion designated for transit projects out of a list that totals $5 billion.

That would leave $2.2 billion for road projects, plus an additional $1.1 billion that the tax is expected to raise for cities and counties to spend on smaller projects.

Included on the $5 billion menu: $917 million for a high-capacity Cobb County transit line reaching Cumberland Mall, $700 million for partial funding of an Atlanta Beltline streetcar system and $1.1 billion for MARTA's new Clifton Corridor line to Emory University. Those projects are on ARC's suggested list.

Fair Share, however, seeks to restore $463.6 million for the Clayton line extending into Spalding County -- which would be jointly funded by another region's taxes since Spalding isn't in the Atlanta region -- and $743 million for light-rail lines reaching Gwinnett Place. ARC's planning professionals -- who declined to comment on the Fair Share list Tuesday -- said they looked at projected ridership in choosing Cobb's line over Gwinnett's and Clayton's.

Johnson said the roundtable's executive committee will discuss including the Clayton line on the final list when it meets Thursday. He said the Gwinnett line is problematic because it would have to run as far as Gwinnett Arena to generate ample ridership, and that would cost $1.1 billion.

Christopher Leinberger, a senior fellow with the Brookings Institution who has analyzed the financial feasibility of an Atlanta-Macon line, will appear in both cities Wednesday to call for its inclusion.

"Atlanta needs to have much better connection to the rest of the state," he said. "This is a way of really addressing that while fulfilling a legitimate regional economic function."