For an idea that barely exists on paper and has the support of neither the mayor nor the City Council, congestion pricing — charging a fee for driving into the busiest areas of the city at the busiest times — has attracted a striking amount of controversy.Last week, Mayor Michael R. Bloomberg, responding to an advocacy group's report about traffic congestion in Manhattan, said that congestion pricing was among several options the city should examine. That rankled opponents of congestion pricing, who released their own report yesterday saying it would hurt retailers and other businesses.The flurry of activity comes as the Partnership for New York City, an influential association of business leaders, is completing a major study of whether congestion pricing would be feasible.The study was to be completed by the end of last year, but its release was delayed until this month, in part because Mr. Bloomberg distanced himself from the plan after he was re-elected in November. At the time, his spokesman said the idea was not on the mayor's second-term agenda.Last week, however, Mr. Bloomberg struck a more moderate tone at a news conference in Harlem, where he was asked about a report by Transportation Alternatives, an advocacy group for pedestrians and cyclists. That report argued that most people who drive private cars into Manhattan south of 60th Street do so for comfort or convenience, not for economic necessity, and could easily switch to mass transit."We are trying to make traffic flow more freely," Mr. Bloomberg said. "There are places in the world that have tried congestion pricing. And it's certainly something that we should be looking at."But the mayor also argued that there were unforeseen drawbacks to many alternatives that looked good on paper — like shifting truck deliveries to nighttime hours and installing speed bumps on busy streets. "The real world is, not everybody is going to use mass transit," he said. "I think it's relatively impractical to take a whole bunch of city streets and say we're just not going to allow cars on them."Stu Loeser, a spokesman for the mayor, emphasized yesterday that Mr. Bloomberg had not changed his views. "The mayor's remarks in Harlem should not be interpreted as a loosening or easing up of his position last November," he said.Even so, congestion-pricing foes have been galvanized into action.The Queens Chamber of Commerce, which has 1,300 members, and Councilman David I. Weprin of Queens released a report arguing that while reducing congestion was "a worthwhile objective," congestion pricing would reduce consumer spending and tax revenues and harm small businesses and commuters who drive. A reduction of 40,000 people entering Manhattan each day could result in a $1.9 billion reduction in spending, according to the report.Parking-garage owners have been fierce critics of congestion-pricing proposals; Vincent L. Petraro, a lawyer who represents the Metropolitan Parking Association, an industry group, is a chairman of the Queens chamber's legislative committee.Supporters of congestion pricing said the report relied on unsound assumptions because it did not consider the lost productivity and wasted time caused by slow-moving buses and cars.Kathryn S. Wylde, president of the partnership, said that London's experiment in congestion pricing, which began in 2003, was a success. "Our conversations with the leadership in London, in government and business, show that they are enthusiastic about the positive results," she said.Peter H. Kostmayer, president of Citizens for NYC, a nonprofit organization that gives grants to neighborhood groups around the city, urged Mr. Bloomberg to remain open-minded. "We're focusing on four problems — congestion, danger, noise and pollution — and we think this is a simple, bold, dramatic step, like the citywide smoking ban, that could solve all four at once," he said.Mr. Kostmayer conceded that congestion pricing was controversial. "It's not consistent with the American ideal that you can do whatever you want, whenever you want," he said.