Facing a showdown at the county line, San Francisco's Board of Supervisors Tuesday backed away from a plan to continue studying a toll for drivers entering the city from San Mateo County. But the idea of charging a toll to pass through the greater downtown area remains alive.

The supervisors, acting as the San Francisco County Transportation Authority, voted 8-3, with Carmen Chu, Bevan Dufty and Michaela Alioto-Pier opposed, to continue studying the concept of charging tolls during the most-congested parts of the day in an expanded area of downtown - but to end consideration of a proposed toll at the San Mateo County line.

Assemblyman Jerry Hill, D-San Mateo, who marshaled the forces against the "southern gateway" toll, was pleased by the decision, and said would not follow through on his threat to pass legislation banning cities from imposing tolls to enter or leave their limits.

"Congestion pricing requires a regional approach," he said, noting that San Francisco never included its southern neighbors in its study. So, for now, San Francisco will confine its consideration of what transportation planners call a "cordon toll" and an entry or exit fee by critics, in a broad section of downtown, bounded by Laguna, Guerrero and 18th streets and the northeastern waterfront.

Two scenarios for the area were outlined in a study that was accepted by the authority board Tuesday, and will face further study if the agency secures the necessary $1 million to $2 million in federal funding. One would charge $3, collected electronically, every time a vehicle passed in or out of the area, with a daily maximum of $6. A more moderate proposal would charge tolls only on vehicles leaving the district in the evening commute hours.

Cordon tolls are designed to reduce congestion by charging fees in crowded areas and at the busiest travel times, and to raise money for transportation improvements.

The San Francisco plan, according to the authority's study, could raise $60 million to $80 million a year. Proponents say the tolls have been a success in London and Stockholm, but the concept has never been tested in the United States.

Federal transportation officials are eager to experiment, and San Francisco is perhaps the leading candidate to win funding for further study, including environmental reviews, and a six-month to one-year experiment that could take place in 2015 or later.

The idea won support from environmental groups as well as pedestrian, bicycling and transit advocates at Tuesday's nearly three-hour hearing, but some merchants said it should be dropped immediately, without further study.

"San Francisco does not need any more taxes on cars," said Tim Leonoudakis, of the San Francisco Parking Association.

Linda Mjellem, director of the Union Square Business Improvement District, said she feared the tolls would drive away business.

"What we gain in congestion fees, we will lose in sales tax revenues," she said.

Authority officials say that in cities with cordon tolls, business has improved.

Jamie Whitaker of the Rincon Hill Neighborhood Association, which sits inside the tolling boundaries, said congestion will only get worse and it's important to start searching for solutions.

"Do we start talking about it now or do we kick the can down the road and let our grandchildren deal with it?" he said.

Despite the excision of the county-line toll from the plan, authority officials are pleased they'll be able to continue studying congestion tolls, and said they don't consider the decision a defeat.

"It was a bit of an overreaction," said Supervisor Ross Mirkarimi, chairman of the authority board. "This was not about implementing a toll proposal. It was about implementing a study."