ALBANY — Critics of Mayor Bloomberg’s congestion pricing plan are charging that the revised legislation under consideration in Albany rests on an accounting trick that makes it appear as if the Port Authority of New York and New Jersey would share in the costs by contributing $1 billion toward the program.

In fact, as critics of congestion pricing are pointing out, the $1 billion is not a new source of money but would be taken out of capital funds that the authority has already set aside for the state under its 10-year capital projects plan, which was approved in December 2006.

“The use of Port Authority funds is a sleight of hand to disguise flaws in the plans,” a Democratic assemblyman of Queens, Michael Gianaris, said.

The money has become a crucial part of the conversation here as lawmakers debate whether to impose an $8 fee on motorists to drive into Manhattan below 60th Street between 6 a.m. and 6 p.m. on weekdays. The revenue would be used to pay for mass transit improvements in the city.

Assembly Democrats, who have been largely resistant to the mayor’s plan, had demanded that New Jersey pay more for the program because New Jersey drivers entering the city wouldn’t face any additional fees, as the tolls they currently pay would be deducted from congestion charges, effectively canceling them out.

Under the revised legislation, if the Port Authority didn’t contribute $1 billion toward the MTA capital plan, New Jersey motorists using the Hudson River crossings would be forced to pay up to $3 more in congestion fees.

“This amended bill also now includes provisions that will make it certain that commuters who use Hudson River Port Authority crossings are contributing their share of revenue to the MTA capital plan, which will result in more funds for mass transit improvements throughout our region,” Mr. Bloomberg said in a statement.

After the amended bill was announced, critics of congestion pricing in the Legislature wondered where the Port Authority money would come from.

A high-level Assembly aide said yesterday that critics were “suspicious” of the source of the funds but hadn’t determined what part of the Port Authority budget would be used.

As it turns out, according to public officials, the authority money exists as unallocated funds for regional transportation projects essentially under the control of New York’s governor.

“Practically, all it would do would be to shift money from other New York projects, and that is a three-card Monte game,” a Democratic assemblyman of Westchester, Richard Brodsky, said.

In 2006, the authority board set aside $2 billion to both New York and New Jersey for undetermined projects.

Initially, Governor Pataki had planned to use the money to help finance the construction of a rail link between Lower Manhattan and John F. Kennedy International Airport.

When Governor Spitzer shelved the rail link project after he took office in 2007, the money remained unallocated. Mr. Spitzer and now Governor Paterson could have transferred the money over to the MTA, according to public officials.

A spokesman for the mayor said yesterday the governors never portrayed the $1 billion as new state capital funds, but said the amended bill provided an assurance that the money would be allocated to the MTA.

Yesterday, Assembly Democrats resumed discussions of the bill in a private conference meeting at which the overwhelming majority expressed opposition. The speaker of the Assembly, Sheldon Silver, is expected to decide this weekend whether to bring the bill to the floor for a vote on Monday, the deadline for the city to qualify for $354 million in federal aid for the program.

Mr. Bloomberg spent yesterday calling lawmakers directly and asking them to support the bill.