Suburban commuters who hoped a regional transportation vote could finally build rail lines outside Fulton and DeKalb counties received a deep blow in negotiations Thursday.

A project that could have built a rail line from MARTA’s Arts Center station to the Cumberland area of Cobb County lost $167.5 million in regional funding from the proposed project list. Instead, that money would go to road projects — such as an interchange at I-75 and Windy Hill Road.

Nothing, though, is final until 21 local officials — a regional “roundtable” — approve the entire $6.1 billion list. Next year, voters will consider a 1 percent sales tax to fund the projects, in a vote that is seen as critical to the region’s future.

The Cumberland line was the last construction project on the list capable of breaking the borders of Atlanta’s Fulton and DeKalb rail district, established four decades ago with the MARTA system.

The $689 million remaining for the Cobb transit project likely would not be enough to build a rail line on its own. Local officials still hope to fill the gap with some other source of funds, such as federal grants.

Atlanta Mayor Kasim Reed, one of the 21 mayors and county commissioners putting together the list for next year’s vote, acknowledged Thursday that the remaining projects on the list are not the grand plan once envisioned.

“I don’t think it’s a regional rail plan,” Reed said. “I think it’s the beginnings of one.”

New rail aside, significant chunks of money have been earmarked for buses, such as $100 million for restoring Clayton County’s local bus service. And MARTA would get several hundred million dollars for repairs and upgrades.

Other remaining proposals slated for next week — the roundtable has an Oct. 15 deadline — stirred heated debate Thursday, including two that would take money from MARTA and other transit projects and give it to Georgia Regional Transportation Authority Xpress commuter bus service.

The once-sprawling map of rail expansion proposals on the wish lists that counties and project advocates put together shot rail lines far into the suburbs, including Cobb, Gwinnett, Clayton, Henry and Rockdale counties.

It was always clear there was not enough money to build them all.

The state economist estimated the tax will bring in $6.14 billion for projects of regional significance over 10 years, and about $1 billion for smaller local projects.

The project list provides a foundation for future suburban rail expansion, should another source of funds appear. Besides the Cobb line, there’s $95 million for studying and engineering for a transit line into Gwinnett County.

And within DeKalb and Fulton counties, likely rail projects to the Emory University area and along the intown Beltline are marked for construction funds.

There are other amendments left to consider in final meetings next week, such as whether to add preliminary money for a southern commuter rail line, which would benefit distant suburban counties, and whether to add more money to a proposed transit line along eastern I-20.

That I-20 line is currently marked for $225 million for a commuter bus system.

Both projects have received questionable support from the roundtable so far.

DeKalb County Commissioner Larry Johnson, who has argued for the eastern I-20 funding but is not on the roundtable, acknowledged it didn’t look good. He hoped additional I-20 transit money would elevate the project from bus to rail.

“We’re not going to get our rail to I-20,” Johnson said, deploring transportation funding levels for south DeKalb County. “You got people who paid [the MARTA tax] for 30 years and now they’re going to pay an extra penny” and still not get the services they need, he said. “It’s a travesty.”

As for Cobb’s hopes for a rail line, the county hopes to know about its chances for securing a federal grant in early 2013.

Should efforts to secure federal grants fail, the amount allocated from the local tax, if it passes, would at least launch a rapid bus line in Cobb County, all the way to Acworth, said Atlanta Regional Commission staff.

That northern bus line takes money that could have gone toward a rail line to Cumberland. If more funding became available, that bus line could always be turned into a train line.

The changes made Thursday were proposed by Cobb’s representatives to the roundtable, in the hopes of satisfying those who wanted the money spent on roads and complained bitterly in public meetings about the possible rail line.

And those who wanted the rail line had complained that it did little for people farther north within the county.

“We responded to public input,” said Cobb County Commission Chairman Tim Lee. He insisted that the county would work hard for completion of the rail line, and that conversations with federal officials so far went well.