Advocates of a London-style congestion pricing plan for New York are hoping to win a long-sought endorsement from Michael Bloomberg, the mayor, when he sets out a sweeping vision for the city in an address on Saturday.

The idea of a congestion charge has had supporters in Mr Bloomberg's administration for years but the mayor has stopped short of making it a priority because he considered the political fight to be unwinnable.

He called the idea a nonstarter as recently as December while acknowledging a serious congestion problem.

But people on both sides of the debate said on Friday they believed he would present a plan on Saturday.

They say Mr Bloomberg believes he has built enough support to overcome the opposition, which includes business and neighbourhood groups from the commuter-rich Queens borough and owners of parking garages.

Press reports said on Friday the city was poised to introduce a plan to charge motorists up to $8 to enter the most congested business districts in Manhattan. The mayor's office would not comment on the reports.

Kathryn Wylde, chief executive of the Partnership for New York, a business group, is optimistic. "We believe congestion pricing is the key to New York City's transportation future," she said. "It provides a source of revenues that will fund a transportation system [expansion] that will allow the city to continue to grow."

City planners estimate New York will add 1m new residents in the coming decades. Mr Bloomberg's address tomorrow, to coincide with Earth Day, is expected to detail a comprehensive plan to accommodate dramatic population in-creases while also making New York a greener city.

"Certainly congestion pricing near or at the top of our list" of policies, said Paul Seely White, executive director of Transportation Alternatives, a group that seeks to reduce car traffic.

Mr Bloomberg was also working to keep New York competitive with London in financial services. At a lunch on Thursday, he handed out to some of the biggest US political donors cards that showed a list of New York's legislative priorities and he encouraged the donors to press the city's agenda when politicians called to ask for donations.

Number three on the list was: "Congress must ease the impact of restrictive visa and immigration policies and complex Sarbanes-Oxley regulations in order for New York City to remain the financial capital of the world."