Mayor Bloomberg’s year-long quest to persuade the state Legislature to agree to congestion pricing — a crucial piece of his long-term environmental and sustainability blueprint known as PlaNYC — appears to have fallen short, lawmakers said yesterday.

Assembly Democrats, who have been the main bloc of opposition to the anti-traffic plan, said most of their members are resistant to the idea of charging weekday motorists an $8 fee to enter the busy parts of Manhattan, and expressed doubt that the legislation would even come to the floor for a vote. “Proponents of congestion pricing need a miracle right now,” a Democratic assemblyman of the Bronx, Rubén Díaz Jr., said last night.

Supporters insisted last night that high-level talks are ongoing. Federal officials have set a deadline of today for the Legislature to pass a congestion pricing plan in order for the city to qualify for about $350 million in transportation funds.

The diminishing prospects for congestion pricing mean that the mayor will likely need another extension from the federal government, which has already pushed back the approval deadline more than once.

To revive the plan, the mayor would probably have to shrink the scope of his proposal, which calls for a smaller congestion zone than bigger than 25 blocks around Midtown.

Yesterday, Mr. Bloomberg told reporters that the “time for changes” has passed, at least in the context of securing support today. “You can’t write complex legislation that has enormous impact on the city for generations in two hours and expect to get it right,” he said.

Lawmakers interviewed said they doubted that the speaker of the Assembly, Sheldon Silver, who rarely permits bills to be voted on unless he’s certain they have enough votes to pass, would bring congestion pricing to the floor.

Mr. Bloomberg said he would consider such an outcome an insult to constituents, whom he said would benefit from mass transit improvements financed by revenue generated by congestion pricing.

“The one thing they can’t do is walk away without a vote. That would be, I think, just unconscionable,” he said. “People if they are going to vote it down have to stand up, and then they are going to be responsible to their constituents as to why they don’t have buses, don’t have faster, better buses, newer buses, don’t have all of the technology, all the improvements to the subway line.” A source close to the speaker said Mr. Silver was trying to find a way to let the mayor down easy. “I don’t think he wants to rub the mayor’s face in it. He’s trying to be gracious about this thing. He just wasn’t able to help him on it,” the source said.

The Bloomberg administration has put a prodigious amount of resources and man-hours into developing the congestion pricing plan and lobbying on its behalf. They scored a victory last week when the New York City Council endorsed the proposal and kicked up to Albany for debate. Governor Paterson last month also endorsed the traffic tolls.

Mr. Bloomberg has less influence over Mr. Silver, who three years ago squashed his plans for a West Side stadium, than he does over the City Council members. The billionaire mayor gained support among Senate Republicans after delivering pledges of much-needed financial support. Assembly Democrats have accused the majority leader of the Senate, Joseph Bruno, of holding up budget talks until lawmakers agreed to insert congestion pricing legislation into a larger budget language bill.

A Republican senator said the Senate would not vote on congestion pricing unless the Assembly also took it up. “Putting a bill on the floor doesn’t get us a result,” the senator said.

Unlike the Senate Republicans, Assembly Democrats enjoy a veto-proof majority and thus were less susceptible to rewards from the mayor, such as contributions or endorsements.

Opposition in the Assembly is strongest among representatives of Queens, the Bronx, Brooklyn, Long Island, and Westchester. Some lawmakers said there was little the mayor could do to change their minds due to unpopularity of the plan among their constituents and a fear that the proceeds would be squandered by the Metropolitan Transportation Authority.

Some lawmakers insisted, however, that Mr. Bloomberg could have won them over by allowing more categories of exemptions, such as motorists working for not-for-profits, or by agreeing to a sunset measure.