While Mayor Bloomberg publicly maintains that the city is not interested in charging drivers a fee to enter Midtown Manhattan’s business district during its busiest hours, four independent groups are quietly conducting studies to determine how imposing such a charge could reduce city traffic and benefit the economy.

The studies, set to be released within the next few months, could renew pressure on the mayor to consider instating the fees known as congestion pricing.

Congestion pricing creates a financial incentive to reduce the number of cars on the city’s most overcrowded streets and encourages the use of mass transit. Opponents say they don’t like the idea of New Yorkers paying to use their own city.

Congestion pricing was adopted in London three years ago, but has become a political lightning rod in New York because of opposition from non-Manhattan residents who say the burden of the charge would fall more on them than on Manhattanites.

The Partnership for New York City, a group of 200 CEOs from New York’s leading investment firms, will release a study in two weeks on the impact of traffic on the city’s economy.

“Congestion is a serious problem and other cities are finding solutions,” the president and CEO of the partnership, Kathryn Wylde, said. “There’s been a lot of analysis of air pollution, health effects, and fuel costs of congestion, but there really hasn’t been anything on what impact traffic congestion has on the cost of doing business in the city.” Congestion pricing, along with greater enforcement of parking regulations and improving mass transit options, is one option the group is studying.

The Manhattan Institute, a think tank, on December 7 plans to release its study on what New Yorkers think of congestion pricing.

The Regional Plan Association, a nonprofit organization, is researching technologies needed to implement congestion pricing, and will release its study in the next few months, according to a spokesman.

The East Midtown Association, a business improvement district that covers 48 blocks, has yet to take a formal position on the issue. Its president, Robert Byrnes, said there is “unofficial consensus among board members in support of it.” The group plans to commit resources to a traffic study at the end of this month.

“I don’t think you can have a serious conversation about the future of New York without talking about road pricing,” the executive director of Transportation Alternatives, Paul Steely White, said. In a new study, Transportation Alternatives is also proposing a trial for New York of congestion pricing.

City Council Member David Weprin, who represents eastern Queens, has emerged as the leading critic of congestion pricing.

“There are people in Eastern Queens and Staten Island and other parts of the city who are not near public transportation. I don’t want to discriminate against those individuals,” Mr. Weprin said.

In London, where drivers pay $14 to enter the tolled zone of the city during peak hours, it has been reported that the area’s traffic has been reduced by about 30% at those times.