SAN FRANCISCO – After weeks of intense lobbying from environmentalists and a supermarket trade group, city lawmakers approved a ban Tuesday on plastic grocery bags, a first for a U.S. city. The law adopted on a 10-1 vote requires large markets and drugstores to give customers only the choice of bags made of paper that can be recycled, plastic that breaks down easily enough to be made into compost or reusable cloth. San Francisco supervisors and supporters said that by banning the petroleum-based sacks blamed for littering streets and choking marine life, the measure would go a long way toward helping the city earn its green stripes. “Hopefully, other cities and states will follow suit,” said Supervisor Ross Mirkarimi, who crafted the ban after trying to get a 15-cent per bag tax passed in 2005. The new breed of bags “offers consumers a way out of a false choice, a way out of the paper or plastic dilemma,” Noble said. 160Want local news?Sign up for the Localist and stay informed Something went wrong. Please try again.subscribeCongratulations! You’re all set! The 50 grocery stores that would be most affected by the legislation argued that the ban was not reasonable because plastic bags made of corn byproducts are a relatively new, expensive and untested product. Some said they might offer only paper bags at checkout. “I think what grocers will do now that this has passed is they will review all their options and decide what they think works best for them economically,” said David Heylen, a spokesman for the California Grocers Association. Mayor Gavin Newsom supported the measure and is expected to sign it into law. The switch is scheduled to take effect in six months for grocery stores and in one year for pharmacies. Craig Noble, a spokesman for the Natural Resources Defense Council, said it would be disappointing if grocers rejected the biodegradable plastic bag option since more trees would have to be cut down if paper bag use increases.