The closing of a historic bridge in Kennett Township two weeks ago has reignited a battle between county officials and preservationists that has become a proxy for a debate over the future of development in southern Chester County.

County and state officials want to replace the current one-lane, 101-year-old Chandler Mill Bridge, which was closed for structural deficiencies, with a modern two-lane bridge that could handle more traffic and would, they argue, be safer.

Community activists, on the other hand, say a new bridge would increase traffic and endanger the rural nature of the area, which includes 400 acres of preserved land along the scenic West Branch of the Red Clay Creek.

Add to that the fact that the bridge is on the National Register of Historic Places, which gives it certain legal protections, and you have a fight that could drag on for years.

Dee Durham, executive director of Safety, Agriculture, Villages and Environment Inc. (SAVE), argues that the bridge closing provides a perfect opportunity for the county to follow through with her group's proposal, which is to replace the deck and failing supports of the existing structure.

That "could pretty much accomplish everybody's goals," she said, adding that the bridge, which handles more than 600 cars a day, could be reopened in a matter of months.

Repairs to the one-lane structure would cost about $500,000, according to a SAVE-commissioned study. A full bridge replacement would cost $1.7 million and take several years, the study said.

The county said its engineer was working with the Pennsylvania Department of Transportation on a final report that will lay out a plan for the bridge.

PennDot portfolio manager Tim Stevenson, who is overseeing the project for the state, said that no decision had been made yet, but that the closing had caused the state to "accelerate" its work.

"The closure took us by surprise," he said, adding that, based on the latest inspection, the bridge should handle only three tons. A school bus that regularly crossed the bridge weighs significantly more than that, he said.

The closing has breathed new life into a long-running saga that began in 2005, when county officials announced plans to demolish the span.

Activists led by SAVE petitioned the National Park Service to add the bridge to the National Register of Historic Places in January 2010, citing its significance in local transportation history.

The Pennsylvania Historical and Museum Commission challenged that designation, arguing that the county had 17 or 18 similar bridges.

The state lost its appeal, and the bridge remained on the list of protected structures.

That gives activists a foothold to continue urging rehabilitation.

Though federal law won't ultimately prevent the county from taking the bridge down, it does require consultation with stakeholders, including SAVE, whenever a project would have an adverse effect on the bridge's historic nature. Some types of renovations could also trigger the requirement.

Meanwhile, activists are trying to get out in front of whatever plan PennDot and the county put out.

They argue that widening the bridge would irreparably change the feel of the rural area.

Gwendolyn Lacy, executive director of the Land Conservancy for Southern Chester County, warns that a larger bridge could adversely affect recreation paths and draw traffic to quiet side streets after the White Clay Point development is completed a mile away on Route 41.

The bridge currently acts as a choke point, she said, because cars can go in only one direction at a time.

And Tom Mills, who lives next to the bridge, calls it "the essence of Chester County."

"It's a thing that everybody really appreciates," he said.

Contact Anthony Campisi at acampisi@phillynews.com.