Advocates argue that a soda tax would reduce consumption and pay for anti-obesity campaigns. In an opinion piece in The New England Journal of Medicine last year, Dr. Brownell and Thomas R. Frieden, the director of the C.D.C. and former New York City health commissioner, estimated that in New York State alone a penny-per-ounce soda tax would raise $1.2 billion annually.

Small excise taxes on soda are already in place in Arkansas, Tennessee, Virginia, Washington and West Virginia, and Chicago imposes a 3 percent retail tax on soft drinks. Soda taxes were proposed in at least 12 other states in 2009, though none were approved. Mississippi is considering legislation that would tax the syrup used to sweeten soda; the mayor of Philadelphia is weighing a tax on soda and other sugar-sweetened drinks, and Gov. David Paterson of New York recommend a penny-per-ounce tax on sugared beverages in his proposed state budget last month.

The penny-per-ounce tax, favored by Dr. Brownell and others, would produce a significant increase in retail costs: the 12-pack of Coke on sale for $2.99 would go for $4.43 and a 75-cent can would rise to 87 cents. These increases, Dr. Brownell estimates, would reduce the annual per capita consumption of soda by more than 11 gallons, to 38.5 gallons. “And the revenue,” he says, “could be used to subsidize fruits and vegetables, fund obesity prevention programs for children and home economic classes in schools, and more.”

The model, clearly, is tobacco. Dr. Frieden, who promoted a soda tax when he was a health commissioner, sees further parallels between soda and tobacco: “There are aspects of the food industry that are reminiscent of tobacco — the sowing of doubt where there’s no reasonable doubt, funding of front groups, use of so-called experts, claims that new products which are safer for consumers are available, and the claim that they are not marketing to children.”

The public war against tobacco has worked, if imperfectly: Americans smoke at half the rate they once did, half of all smokers have quit, and the tobacco companies finance strong antismoking campaigns.

In the case of tobacco, the health risks of smoking were clear. But the beverage industry contends that science does not back up the assertion that childhood obesity is even partly caused by soda consumption, and has sought to make the discussion about personal choice and freedom. “Soda has calories, and food with calories causes people to put on weight when consumed in excess,” says J. Justin Wilson a self-described “libertarian consumer advocate” and senior research analyst for the Center for Consumer Freedom, an industry-sponsored advocacy group. “But there is no unique link between soda and obesity.”

Besides, says Ms. Neely, the industry is taking measures: “The beverage industry supports real solutions to obesity and continues to step up to do its part. We’ve removed full-calorie soft drinks from schools across the country and, in support of Mrs. Obama’s initiative, will place the full calories for our products on the front of our containers.”