The idea is to charge drivers for entering the most heavily trafficked parts of Manhattan at the busiest times of the day. By creating a financial incentive to carpool or use mass transit, congestion pricing could smooth the flow of traffic, reduce delays, improve air quality and raise the speed of crawling buses.

To be sure, it is far from being a reality, or even a complete proposal – when pressed, the mayor’s spokesman said it was not on his second-term agenda. Yet the Partnership’s work suggests a plan that, if carried out, could profoundly alter the way New Yorkers and those visiting the city use their cars.

Congestion pricing is the focus of a nine-month study by the Partnership, a group with great influence at City Hall, and participants have provided the first rough outlines of how such a plan might work.

The 840,000 cars that enter Manhattan south of 60th Street on an average weekday could be subject to a $7 charge during peak hours. Vehicles starting and ending their trips within that zone might pay a $4 charge. Several roadways would remain free, like the West Side Highway and the Franklin D. Roosevelt Drive on the East Side, according to people with knowledge of the study.

Drivers could be required to prepay traffic fees, either online or at street-level vending machines. Video cameras would capture license plates of vehicles in the payment zones, and allow the city to match cars to accounts, people familiar with the study said. Failure to pay would result in a fine. No toll barriers would be involved.

Raising money would not be the main goal – although millions of dollars could be collected and funneled into subways, buses, commuter trains and bridges. The video cameras would be at street intersections, and tolls would not be charged on the East River bridges – a prospect that doomed previous proposals, including one Mayor Michael R. Bloomberg advanced in 2002.

City officials acknowledged that Mr. Bloomberg had always been interested in some type of congestion-pricing model, but had said that he considered tolls on the East River bridges politically daunting.

And while officials said some sort of business-district traffic charges could conceivably be workable, they would have to seriously consider what sort of political fight that would bring.  They stressed that congestion pricing was a battle Mr. Bloomberg would not wage if it distracted from his other priorities, like education and crime reduction.

“Although we’re always open to ideas from the business community, this isn’t on the mayor’s second-term agenda,” said Edward Skyler, a spokesman for the mayor.

Even so, several administration officials have discussed the plan with the partnership, and Michael Primeggia, the deputy commissioner for traffic at the city’s Transportation Department, has said publicly that congestion pricing should be considered. The Partnership intends to complete its study by the end of the year and to present it to the administration, which the business group hopes will do its own study.

In London, where congestion pricing began in February 2003 after a year of planning, traffic has been reduced by a third and some bus lines are moving twice as fast. Officials are so satisfied that they intend to nearly double the size of the congestion-pricing zone in 2007. One thing seems certain: New York would not charge nearly as much as the $14 it takes to drive into London’s financial district during the day.

“Is there an opportunity to create a congestion-relief zone that would help this global city?” asked Ernest Tollerson, a senior vice president at the Partnership. “This is a city that wants to add tens of thousands of jobs, but we can’t continue to build streets and roads. For the long-term growth of the city, we need demand-management tools.”

Mr. Tollerson oversees a working group that includes five engineering and construction firms, Parsons Brinckerhoff, STV Group, Washington Group International, Siemens and D M J M Harris; a consulting firm, Booz Allen & Hamilton; and two prominent advocacy groups, Environmental Defense and the Natural Resources Defense Council.

The team has met about once a month since April, and technical analysts have been going through reams of authoritative traffic data from the New York Metropolitan Transportation Council, an intergovernmental body that measures traffic for air-quality and planning purposes.

Andrew H. Darrell, the New York regional director at Environmental Defense, said that 80 percent of the cancer-causing substances inhaled by New York City residents comes from tailpipe emissions. “Most people think of traffic congestion in the same way they think about lousy weather – it’s too bad but you can’t do much about it,” he said. “There is no other tool out there as effective as congestion pricing for cutting traffic congestion in a big city like New York.”

In London, he said, congestion pricing led to a 20 percent reduction in carbon dioxide emissions and a 12 percent cut in emissions of harmful particulates and nitrogen oxides, the main components in smog.

Walter B. Hook, executive director of the Institute for Transportation and Development Policy, which works to reduce automobile dependence worldwide, said congestion pricing was still a fairly new idea. “For a long time people thought it was political suicide to implement congestion charging,” he said. Singapore, Oslo and Riga, the capital of Latvia, have all experimented with charging for driving in town.

The most extensive congestion pricing plan, in London, was pushed by an activist (and populist) mayor, Ken Livingstone, and overseen by a transport commissioner, Robert R. Kiley, who happens to be a former president of the Partnership for New York City and a former chairman of the Metropolitan Transportation Authority. Mr. Kiley has urged other cities to consider the London model.

Under the plan, drivers are charged a daylong flat fee of £8 ($14) to enter the so-called congestion zone, an eight-square-mile area around London’s financial district.

Officials ruled out using “smart cards,” similar to the E-ZPass toll-payment devices used on many bridges and tunnels on the East Coast, as cumbersome. Instead, 700 video cameras capture multiple images of license plates of cars that drive through the zone between 7 a.m. and 6:30 p.m., except on weekends and holidays.

Computers process the images, matching the license plates photographed against a database of drivers who have paid their congestion fees.

Drivers pay in advance, online, over the telephone or at machines at stores across London. Failure to pay by 10 p.m. on the day of the trip results in higher fees or fines up to £150 ($261). Disabled drivers and residents of the congestion zone are exempt, as are cars that have 9 or more seats or run on electricity or natural gas.

The Federal Highway Administration is spending $59 million through 2009 to study congestion pricing. San Francisco is exploring how a plan like London’s could be adopted. “The focus would be on where we have the most serious and chronic congestion,” said Tilly Chang, deputy director for planning at the San Francisco Country Transportation Authority.

She, too, said the program might rely on easy-to-install cameras rather than transponders, the term for toll-payment devices like E-ZPass or FasTrak, which is used on the Bay Bridge. “The benefit of using cameras is that they can roll out quickly,” she said. “You don’t need transponders.”

There is some precedent locally for congestion pricing. In January 2001, the Port Authority of New York and New Jersey authorized higher tolls during peak hours on its Hudson River crossings, including the George Washington Bridge and the Lincoln and Holland Tunnels.

Congestion pricing in New York City would probably require approval of the City Council and the State Legislature, and skeptics are already grumbling.

“What’s good for London is not necessarily good for New York City,” said Councilman David I. Weprin, a Queens Democrat who led opposition to tolls on East River bridges. But he said he would keep an open mind to a Manhattan-centered plan that did not unfairly burden residents of the other boroughs. “I’d have to look at it, but my gut reaction is it would be a nuisance tax,” he said.

Carolyn Marshall and Jim Rutenberg contributed reporting for this article.