Sonoma County supervisors on Tuesday advanced a proposal to ban plastic bags now given out to shoppers at grocery and other retail stores, but called for a single ordinance that would apply countywide.

The ban would start in July 2013 and apply to what are termed "single-use carryout bags." It would not extend to bags used to hold meat and vegetables, or apply to restaurants. It also would levy a 10-cent fee for paper bags, which merchants would collect and keep. That fee would rise to 25 cents a bag in 2014.

A fine schedule starting at $100 and rising to $500 for a third violation in a year would be included.

Not yet settled are questions about who would enforce the ban and whether it would be the same countywide or perhaps vary among cities, an option that store owners oppose.

The supervisors' unanimous action signaled their clear support for a ban.

"The time has come," Supervisor Mike McGuire said. "We've discussed this for the better part of half a decade now."

But the board also stated its preference for one countywide ordinance. It gave its representative on the Sonoma County Waste Management Agency -- which would adopt and administer the ordinance -- the authority to support only that option.

"What's most important to me is consistency. It gives a level playing field," Supervisor Efren Carrillo said.

At the Mendocino Avenue Safeway on Tuesday, Alan Lockler said he would favor a ban. "Much as I hate to lose the convenience, I think it's a good idea. I'll give it up to save a duck," he said, referring to wildlife becoming entangled in discarded bags.

Similar proposals elsewhere have spurred complaints of over-regulation, but none were voiced Tuesday and supervisors said it would help the environment.

"This is about protecting our rivers, protecting our coast, protecting our creeks," said Carrillo. "This is long overdue."

The ordinance also would move the county toward its goal of diverting 90 percent of curbside and drop-off waste from the landfill by 2020, said Supervisor Shirlee Zane, the board chairwoman.

"The only way we're going to reach that . . . is to have these kinds of policies in place," she said.

Supervisor David Rabbitt asked how much it would cost to produce the environmental report required before a ban could take effect and then to enforce it.

"I think we really need to come to grips with that before we go too far down the line," he said.

The environmental report cost had been estimated at $100,000, as had the annual cost of managing the ordinance, said Patrick Carter, the Sonoma County Waste Management Agency's program manager. However, he said, they are now expected to come in lower.

"We think there is going to be a lot of self-enforcement going on," on the part of shoppers, he said.

The ban has been studied since 2008 and advocates said Tuesday that the county is behind the environmental curve.

"When we started . . . we may have been leading a little bit," said Ken Wells of the Sierra Club. "At this point, more than half the planet's population has a bag ban. We're not leading anymore. Bangladesh has a bag ban."

Ukiah, Fort Bragg, Mendocino, San Francisco, San Jose and Alameda County are among other jurisdictions in the state that have adopted bans.

With the supervisors' action, the board of the Sonoma County Waste Management Agency can begin the process of completing a draft of the ordinance. The agency is now reviewing proposals to conduct the environmental review.

The county's nine cities have said they support a ban, but Sebastopol, Cloverdale and Rohnert Park have yet to agree to a countywide version.

Waste agency staff are to meet with each of those remaining three cities by the end of August.

"Everyone that we've gone to so far has felt that the countywide one is the way to go," Carter said.

You can reach Staff Writer Jeremy Hay at 521-5212 or jeremy.hay@pressdemocrat.com.