San Francisco ? In this city known for producing laws both path-breaking and contentious, legislators have forcefully stepped into another debate — this time over the potential danger of cell phone use.

With the Board of Supervisors’ 10-1 vote in favor of an ordinance Mayor Gavin Newsom has indicated he will sign, San Francisco has waded into the as-yet unresolved debate over the relationship between long-term use of cell phones and health problems such as brain tumors.

It would be the country’s first law requiring cell phone retailers to disclose the phones’ specific absorption rate, or SAR, to customers.

SAR measures the maximum amount of radiation absorbed by a person using a handset. The Federal Communications Commission limits SAR to an average of 1.6 watts per kilogram of body tissue, but information about radiation levels is not usually readily available when people purchase phones at stores.