With four weeks left to persuade city and state lawmakers to approve a plan to ease traffic in Manhattan, Mayor Bloomberg and Governor Spitzer have begun a complex negotiation over legislative wish lists.

The mayor has until March 31 to get legislative backing for his plan to charge motorists an $8 daily fee to drive into Manhattan below 60th Street in order not to forfeit about $350 million in federal funds that would help pay for the program.

Whether Mr. Bloomberg and the governor, whose administration is close to completing a draft of a congestion pricing bill, succeed in securing enough votes will to a large extent come down to the outcome of a horse trade with lawmakers who have withheld their support for the legislation but have indicated they are open to talks.

Since Mr. Bloomberg began promoting his plan last year as a long-term way to relieve traffic, improve environmental quality, and pay for improvements to the mass transit system, he has encountered resistance from suburban and outer-borough lawmakers who have criticized the proposed toll as a regressive tax and have questioned how the money raised would be spent.

“It’s a hard vote to cast because it’s been falsely painted as a new tax on the middle class,” the president and CEO of the Partnership for New York City, Kathryn Wylde, said.

Lawmakers and officials close to the issue say the upcoming negotiations are likely to be wide-ranging and move into areas that don’t relate to mass transportation. Deals could encompass promises of more express bus lines and new subway stops but also grants for affordable housing or political contributions, sources say. Mr. Spitzer is also likely to offer as a carrot a pay raise for state lawmakers.

While the general consensus in Albany is that mayor’s and the governor’s hunt for votes will likely fall short, even the firmest critics of congestion pricing in the Legislature say it’s too early to pronounce the mayor’s plan dead.

“On a scale of 1 to 10 — one being completely dead and buried and 10 is jumping for joy — I’d give it a 2 and a half,” a Democratic assemblyman who opposes the traffic tolls said.

“Of course, it’s not dead. It’s ridiculous to assert it’s dead,” a Democratic senator of Manhattan, Eric Schneiderman, said.

The plan first needs to go before the City Council. If a majority of city lawmakers approve it, the State Legislature then must consider the legislation. It’s unlikely, however, that the City Council will back the plan unless it has assurances that state lawmakers will also stand behind it.

In Albany, congestion pricing has largely floated above the recent turmoil generated by the Senate Republicans’ weakening hold on the majority. It’s one of the few issues where Mr. Spitzer and majority leader, Joseph Bruno, are in agreement, with both favoring some version of the plan.

Mr. Bloomberg, who recently donated $500,000 to the Senate Republicans, has secured support from most of Mr. Bruno’s conference. On Tuesday, the mayor is sending one of his top deputies, Edward Skyler, to Albany to gather support from more lawmakers.

Assembly Democrats pose the strongest challenge to the mayor. Their leader, Speaker Sheldon Silver, who represents a district in Lower Manhattan, told The New York Sun last month that his position on congestion pricing had “evolved” and that he would consider supporting it if several conditions were met.

Mr. Silver said he would not sign on to a plan unless it included some form of a rebate for lower-income motorists. He suggested giving a break to people who regularly drive into Manhattan for work and earn less than $75,000.

He is also demanding a special toll for New Jersey commuters crossing the Hudson River. Under the congestion plan that was recommended by a state commission earlier this year, drivers entering the city from New Jersey would not have to pay a congestion fee during rush hours because the tolls they already pay to use the bridges would cancel out the $8 charge.

The speaker, who is pushing for the completion of the Fulton Street Transit Center, said his support would also hinge on how the congestion money is distributed for capital transit projects.

Even if Mr. Silver’s demands are met, it’s far from clear whether he can deliver enough votes from his conference. “There are people who are very much opposed. There are people who are very much in favor,” he said.

The bartering in Albany will take place in the context of broader negotiations over the budget, which lawmakers are also required to pass by the end of the month. Supporters of congestion pricing view the timing as an advantage by giving lawmakers more political cover. Lawmakers, they say, would be less likely to vote for congestion pricing if it were a stand-alone bill.

Spitzer and Bloomeberg officials said a five-year, $29.5 billion spending plan put out last week by the Metropolitan Transportation Authority demonstrates the need for congestion pricing at a time of economic turbulence.

The transit authority included in its plan $4.5 billion that it said could be generated by borrowing against congestion fees. The MTA said the city and state needed to raise $10 billion in revenue to pay for the plan. Without congestion pricing, officials said, the gap would grow by billions of dollars.

Congestion pricing would be “one of the most reliable revenue sources in the whole capital plan,” Mr. Skyler told the Sun.