Within 48 hours, Georgia’s business and political elite will cock their ears and listen for a chirp from the canary lodged deep in a very large coal mine.

Should they find nothing but feathers, the backers of next year’s major sales tax initiatives in Georgia — which include regional votes for transportation — will spend the next year in a cold sweat.

On Tuesday, Cobb County voters will be asked whether they want to continue a general-purpose local option sales tax expected to raise $492 million over four years for parks, public safety, libraries and transportation.

It is a small, local affair. But Cobb is one of the richest veins of Republican votes in the state. Win or lose, those behind next year’s regional sales tax referendums for transportation will be poring over the results. Billions of dollars for road and rail construction are at stake, especially in metro Atlanta.

The impact won’t stop there. Last week, state lawmakers disclosed that a tax overhaul now in the works, to widen the reach of the state sales tax to include such things as cell phone service and car repairs, could require as many as three statewide ballot questions in November 2012.

“If [the Cobb vote] loses badly, that’s as bad an omen as you could possibly have,” said Chuck Clay, a former state GOP chairman and a strategist for the Cobb SPLOST campaign. “It’s a precursor. It’s a road map. I think there are some fundamental differences. But it sure will test the temperature in a critical bloc of votes.”

The last vote on this penny tax in Cobb was in 2005. Victory came with 114 votes to spare. We are now in the throes of the deepest economic slump most of us can remember. Tea partyers, unknown six years ago, are on the march.

Sensing a hostile climate, Cobb politicians have deliberately stayed away from the contest.

“What I’m hearing is that nobody wants to pay for anything, ever, anywhere, and all they want is earmarks. They want their specific project to get done, but they don’t want anybody else’s project to get done,” said state Rep. Judy Manning, a Republican from Marietta. The city is a traditional source of “yes” votes on county tax issues.

West Cobb may be the stronghold of “no” votes. “I haven’t had one come to me and be supportive of that referendum,” said state Rep. Earl Ehrhart, a Republican from Powder Springs.

But anxiety over the Tuesday vote might be overblown. The odds of the Cobb SPLOST passing are actually pretty good.

Since November 2008, 83 county sales tax referendums have been held across Georgia, according to the secretary of state’s website. All but seven have passed. That’s an 8 percent failure rate.

Last Nov. 2, the same day that tea partyers deposed Democrats in the U.S. House, Georgia voters approved 21 of 22 county sales tax referendums worth $1.1 billion. Victories were recorded in Cherokee and Paulding counties — both chock-full of tea party revolutionaries.

Yet there is a fly in that ointment.

Also on Nov. 2, only 14 of Georgia’s 159 counties — Cobb was one of those few — approved a $10 annual car tag fee to create an $80 million trauma care network to span the state.

The advantage that local referendums have is obvious. Every day, voters drive past the projects they approve — whether schools, sidewalks or parks.

That’s why politicians tend to stay out of local referendum campaigns. Let the project list do the talking, the logic goes.

Supporters of next year’s transportation sales tax in metro Atlanta are likely to rely heavily on that approach, said Clay, the Cobb SPLOST strategist.

The Cobb campaign has emphasized public safety projects in the SPLOST campaign. Postelection polling of the Cobb vote will be required to determine what role $132 million in transportation-related projects — also on the SPLOST list — played in voters’ decisions.

Voters in regions of Cobb where excruciating commutes drove sentiment may see their areas targeted next year with transportation projects designed to lure them out to vote again, Clay said.

But supporters of next year’s transportation sales tax campaign won’t be able to rely solely on a laundry list to make their argument. One of the many reasons last year’s trauma care tax failed was the absence of any major Republican figure willing to stand behind the campaign.

While personal endorsements may not be necessary in local referendums, they’re essential in multicounty balloting.

Atlanta Mayor Kasim Reed is certain to be one voice and face of the campaign in metro Atlanta. But his appeals will register largely among Democrats. Reed will need — and want — Republican company.

“I’ve heard it come up in conversations. That’s a really important piece of promotion, giving it a face and a voice,” said Bucky Johnson, mayor of Norcross and chairman of the “round table” in charge of building the project list for the metro Atlanta transportation sales tax campaign.

Cultivation of Republican confidence may be the most important aspect of Tuesday’s vote in Cobb. “You think if it loses, everyone will run for cover?” Johnson asked. No answer was necessary.