Top MARTA officials went before the Clayton County Commission on Tuesday evening to make a case for why the county should join the transit system.

MARTA CEO Keith Parker and Board Chairman Robbie Ashe said the county could shape its own service plan during and after contract negotiations — a plan that possibly could include bus service, heavy rail and commuter rail. And, the county would be joining an already established $6 billion asset, Parker added.

“We hope that we can have that dialogue that will lead us to providing robust service throughout Clayton County in short order,” Ashe told commissioners. “We think that we would be able to do that. We think that is a tremendous opportunity for Clayton County, and a tremendous opportunity for MARTA.”

A bill passed in the General Assembly this year allows Clayton residents to vote on whether to pay a sales tax on top of the existing 6 percent sales tax to start a transit system. Initially there was some confusion about whether the only option was joining MARTA, or if the county could explore other options.

Commission Chairman Jeff Turner said Tuesday that the county now believes the bill only allows the sales tax to be leveraged for joining MARTA. However, Clayton could still pursue other options on its own if it does not pursue a sales tax, for example, a public-private partnership with a private transit provider.

The county has until July 7 to vote to hold the referendum to join MARTA in the Nov. 4 general election.

Since Clayton’s bus service, C-Tran, ended in 2010 due to budget cuts, it is the only core metro Atlanta county that lacks its own transit service.