What's the best use of the old rail line that once carried passengers between Lansdale and Bethlehem?

A revived SEPTA commuter line, to Quakertown in upper Bucks County, and beyond to the Lehigh Valley?

A bucolic "rails to trails" walking path through the exurbs and small towns?

Or both?

The old Reading Co. route is being pulled toward two different futures, separated by a county border.

In Bucks County, planners hope to restore passenger rail service to an area that lost it 29 years ago. Just to the north, in Lehigh and Northampton Counties, workers have removed the old rails to make way for an eight-mile-long Saucon Valley Trail.

In that corner of southeastern Pennsylvania, two national trends - for rails and for trails - converge. And SEPTA, which owns the old Bethlehem route, has a foot in each camp.

Yesterday, the SEPTA board leased part of the route, for $1 a year for 30 years, to the Boroughs of Coopersburg and Hellertown for the recreational trail. Last month, the board gave similar leases to neighboring Upper and Lower Saucon Townships for another part of the eight-mile trail.

At the same time, SEPTA is working with the Bucks County Transportation Management Association on a plan to restore rail service on the same rail line, from Lansdale through Quakertown to Shelly, just southeast of the Lehigh County line.

Throughout the Philadelphia region, competing hopes for long-dormant rail lines might collide, as the rails-to-trails movement meets revitalized efforts to restore train service.

SEPTA is spending up to $100 million in Delaware County to extend commuter train service 3.2 miles to Wawa on the R3 Elwyn line, its first move to restore service after three decades of reducing the Regional Rail network it inherited from the Pennsylvania Railroad and the Reading.

Some of that network, taken out of service years ago, already has been leased for trails.

In Montgomery County, two miles of the out-of-service R8 line between Fox Chase and Newtown is now the Pennypack Trail, a bike-and-pedestrian path along the edge of Lorimer County Park.

Also in Montgomery County, the Cynwyd Heritage Trail in Lower Merion is being built on a two-mile railbed that used to be part of the R6 Cynwyd line, from the Cynwyd station to the Manayunk Bridge.

In Delaware County, the Chester Creek Branch Rail Trail is planned for a long-unused line leased by SEPTA in 2005 to Friends of the Chester Creek Branch.

When SEPTA leases out-of-service railbeds for use as trails, it retains ownership and the right to bring back rail service. But it has never done so, and SEPTA officials acknowledge the presence of a popular trail could make a return to train service harder.

"It could be tricky. Legally, it's still ours, but there would be an outcry from those who have gotten used to it as a trail," said Byron Comati, SEPTA's director of strategic planning and analysis. "But we haven't waived our rights. We're not abandoning it."

"Rail-banking" - using a railbed as a trail - helps preserve an out-of-service corridor from deterioration, vandalism and development, he said.

"Better the right-of-way is being used for something than nothing," Comati said. "We're not abandoning it. We're preserving its long-term viability."

Jon Frey, a Bucks County resident who is leading efforts to restore service on the R8 line to Newtown, said the existence of trails would make it harder to bring back trains.

"I think in the long term it's going to be a significant problem," Frey said. "Once it becomes accepted and popular, a community is not going to want to have it taken away. I don't think anywhere a trail has gone back to passenger rail service."

Jack Cahalan, manager of Lower Saucon Township, said the township's new lease with SEPTA for the trail on the Quakertown-Bethlehem line is going to provide "a real recreational asset" to local residents.

"Once people get out on this trail, they're really going to fall in love with it," Cahalan said, citing historic attractions, geologic features, and the newfound ability to walk between communities. He said the township hoped to have the first section of the trail open for use this year.

He acknowledged SEPTA's right to the property.

"Any time they want to restore the rail service, they just take back the trail," he said. "But if it's vacant, we'd like to use it."

Tom Beil, manager of adjacent Upper Saucon Township, said his township had budgeted $250,000 this year to build a two-mile portion of the trail. He said the township knows it must remove its improvements if SEPTA reclaims the path.

"We viewed it as a huge benefit for our residents," Beil said. "If it's only open for a certain number of years, it's still a benefit for those years."

Tom Sexton, director of the national Rails-to-Trails Conservancy's northeast region, acknowledged there is "naturally a competition" for some corridors, but he said communities have found ways to have both rails and trails.

"There is a way of having our cake and eating it, too," Sexton said, citing so-called Rails With Trails projects that have put footpaths next to active railroads in more than 60 locations.

Nationally, there have not been many efforts to reactive dormant rail lines on trails, said Carl Knoch, manager of trail development for Rails to Trails Conservancy.

By the time the eight-mile Saucon trail is completed in 2015, trains might be using the same railbed about a mile to the south. There, at the crossroads burg of Shelly in Bucks County, is the proposed northern end of a restored rail line from Lansdale.

The latest study of restoring SEPTA service north to Quakertown and on to a park-and-ride lot at Shelly is supposed to be done by spring, said William D. Rickett, executive director of the Bucks County Transportation Management Association.

The Delaware Valley Regional Planning Commission is preparing ridership studies, and if the proposal meets federal guidelines, it would go to the Federal Transit Administration for consideration.

Costs for restoring service from Lansdale to Shelly would be about $110 million to $115 million, with diesel-powered railcars, or more than $300 million if the corridor is electrified to accommodate the existing fleet of electric cars, Rickett said. New cost estimates are being prepared by Jacobs Engineering. SEPTA and the DVRPC would seek the money from the federal government.

Depending on funding, the project might be done in increments, with service extended first to a midway point like Telford, and then to Quakertown and Shelly.

"The key is going to be the money," Rickett said. He predicted service could begin in about 41/2 years, if there were prompt federal approval and funding. SEPTA's Comati said that was probably optimistic.

"The time it takes to restore a line is phenomenal," Comati said, noting that the project to restore service to Wawa has been two years just in design.

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.