This well-heeled town has become the first community on the East Coast to ban plastic shopping bags, a move hailed by proponents as a watershed moment that could lead to a wider change in consumer habits.

"This is a landmark event," said Adrienne Esposito, executive director of the Citizens Campaign for the Environment. Westport "has taken an important and significant step away from a throwaway culture and toward the sustainable future that we as a nation need to embrace."

The measure bans merchants from offering plastic shopping bags, although it does not prevent people from using their own bags. It also does not cover smaller plastic produce bags or bags measuring 28 inches by 36 inches or larger.

Passed Tuesday by a 26-5 vote of Westport's representative town meeting, the ordinance goes into effect in six months. Stores that offer the bags can be fined $150. The ordinance encourages merchants and consumers to use recyclable paper bags or reusable bags.

The General Assembly declined to adopt a similar ban statewide earlier this year, although the measure is likely to come up again in the next session.

"I think most retailers are on board" with the new ordinance, said Nate Paulson, manager of the Patagonia store on Post Road, which does not use plastic bags. Paulson hosted a meeting on the issue for local merchants in July. Many retailers already sell reusable tote bags, and merchants said more and more customers are bringing their own bags.

Patagonia trains staff to ask customers whether they want a bag. "It puts it out there so they can think about it," Paulson said.

"Maybe half the people who come in here decline a bag altogether," said Rita Englebardt, a saleswoman at Max's Art Supplies. "Most of our customers are well aware of the problem with garbage, so they do the right thing."

The ubiquitous plastic checkout bags, used by the trillions around the world, have been the focus of a worldwide campaign because the bags often wind up as litter, blowing in the wind or floating in the sea. The bags can harm marine life, which may become entangled in them or mistake them for food. They can take hundreds of years to decompose.

San Francisco, Oakland, Los Angeles and the island of Maui, Hawaii, have various forms of a ban. A law setting a price on the bags in Ireland has drastically reduced their use there. China, Australia and Germany also require merchants to charge for the bags.

"Those who know Westport ought not to be surprised by this," said First Selectman Gordon F. Joseloff, who said the town has a history of advancing social and environmental causes.

He noted that the town meeting was one of the first municipal bodies to pass a resolution opposing the Vietnam War in the 1960s. Today the town is buying hybrid cars for its departments and has installed solar panels on the firehouse.

But industry advocates argue that the plastic bags take less energy to produce, transport and recycle than paper and that making paper bags pollutes air and water.

Westport town meeting member Judy Starr, who voted against the ordinance, said she is concerned that the new law will drive people to use more paper bags.

"You're taking a litter problem and you're creating a very, very serious potential for a pollution problem in terms of air and water and the use of trees," Starr said.

She said some arguments against the bags are based on faulty information. She said the town should instead encourage recycling and the use of reusable bags and consider putting "a slight tax" on the bags.

Stan Sorkin, executive director of the Connecticut Food Association, which represents supermarkets, food wholesalers and manufacturers, was one of the few people to speak out against the ordinance on Tuesday. Westport is home to a Shaw's and a Stop & Shop, among other retailers.

He echoed Starr's comments.

"Survey after survey has shown consumers prefer plastic bags, but they are throwing them away rather than reusing and recycling them," he said in prepared testimony. "We need to change that mind-set."