San Francisco moved a step closer Tuesday to becoming the first city in the nation to require that retailers post in their stores notices on the level of radiation emitted by the cell phones they offer.

The Board of Supervisors voted 10-1 to give preliminary approval to the proposal. Final approval is expected next week. Supervisor Sean Elsbernd was the lone vote in opposition. Mayor Gavin Newsom, an early proponent of the legislation, plans to sign it into law when it reaches his desk.

Cast by backers as a pro-consumer measure, the ordinance would not ban the sale of certain cell phones but would require retailers to provide the "specific absorption rate" - a measurement of radiation registered with the Federal Communications Commission - next to phones displayed in their shops. Consumers also would be notified about where they can get more educational materials.

"This is about helping people make informed choices," said Supervisor Sophie Maxwell, chief sponsor of the legislation.

But a trade group for the cell phone industry said the law could lead to confusion.

"Rather than inform, the ordinance will potentially mislead consumers with point-of-sale requirements suggesting that some phones are 'safer' than others, based on radio frequency emissions," John Walls, vice president of public affairs for the Cellular Telecommunications and Internet Association, said after the vote. "In fact, all phones sold legally in the U.S. must comply with the Federal Communication Commission's safety standards for (radio frequency) emissions."

The FCC has adopted limits for safe exposure to radiation. The measurement shows the amount of radio frequency energy people absorb in their bodies when talking on a cell phone.

The potential long-term health impacts of cell phone use, particularly on the brain, is still a matter of scientific debate.

A similar right-to-know measure, carried by state Sen. Mark Leno, D-San Francisco, died in the Legislature this year amid heavy lobbying by the cell phone industry.

Small business advocates in San Francisco also lobbied against the local labeling law, saying they didn't have an appetite for more government mandates, particularly in this tough economic climate.

"This is not about discouraging people from using their cell phones," said Newsom spokesman Tony Winnicker. "This is a modest and commonsense measure to provide greater transparency and information to consumers."

The posting requirements would be phased in, beginning in February. Violators would face fines of up to $300. City officials still need to educate retailers and figure out how the law would be enforced, when and if it is finally adopted. Hundreds of stores in San Francisco sell cell phones.

Renee Sharp, director of the California office of the Environmental Working Group, a national nonprofit research and advocacy group, lauded San Francisco for its "leadership in protecting the public's health and right to know, and we hope it's the beginning of a movement that won't stop until everybody shopping for a phone has easy access to this information."