Don't forget your bags.

Signs bearing that reminder are becoming almost as common outside supermarkets as parking spaces blocked by shopping carts. Some local grocers say as many as half of their customers now bring reusable bags.

It seems the disposable plastic shopping bag may be going the way of the incandescent light bulb, replaced by alternatives believed to be more environmentally friendly.

To combat litter, divert trash from landfills and trim the demand for petroleum products, grocers and many other retailers in cities including Malibu, San Jose and San Francisco and unincorporated areas of Los Angeles County are prohibited from packing purchases in handled plastic bags. Stores in those communities also must charge a nickel for paper bags. Marin County supervisors approved a ban last week; so did the Santa Monica City Council. In September, California legislators rejected a statewide ban, but the issue is likely to return this year.

Sonoma County Supervisor Mike McGuire says "it makes sense to study a reduction or even elimination of plastic bags." He is hosting a forum on disposable plastic bags, beginning at 8:45 a.m. Wednesday at Santa Rosa City Hall.

We think a state law makes more sense, for both consumers and retailers, than a patchwork of conflicting policies. And we'd cherish the day when we visited a beach or a park or took a bike ride without discarded bags dotting the landscape. Yet we wonder if banning bags is a real solution.

Supermarkets that can't bag groceries in plastic still are allowed to dispense plastic bags for produce and to sell plastic bags for food storage and as waste basket liners. Some local bans exempt dry cleaners, department stores and restaurants from bag bans. That makes as much sense as promoting recycling with a deposit law that exempts milk, wine and liquor bottles. (Of course, California does exactly that.)

Moreover, according to the bag industry, manufacturing paper bags produces more greenhouse gases and uses more water than manufacturing plastic bags. And a recent study by the Center for Consumer Freedom found that some reusable bags have excessive amounts of lead, making them a potential health threat.

Given the growing momentum (and the ubiquitous litter), a statewide ban still may be the best answer.

Until it's in place, don't forget that grocery stores are required to collect used bags. You also can bag them up and put them in your blue recycling bucket. And, state law or not, when a grocery clerk asks "paper or plastic?" anyone can say, "Neither, I brought my own."