ALBANY — A defeat of congestion pricing in the Assembly may irrevocably rupture the relationship between Speaker Sheldon Silver and Mayor Bloomberg and provoke an open conflict between the two city leaders.

Mr. Bloomberg, who has said repeatedly that he supports politicians who back his policies, might be tempted to do the opposite if his plan to charge motorists a fee to drive into the busy parts of Manhattan collapses in the Assembly, on which Mr. Silver wields tremendous influence.

“The danger could be that it does get personalized,” a former top aide to Mr. Bloomberg, William Cunningham, said. “Could there be a time when the mayor gets fed up with the games? Yes, I suppose so. He’s human.”

The mayor may use his political influence and fortune against Mr. Silver, political insiders say. This year, Mr. Silver, 64, is expected to face at least two Democratic primary opponents in September. Mr. Bloomberg could go as far as to endorse and provide financial support for one of the challengers.

In the past, Mr. Silver, famous for his poker-faced negotiation tactics, has relished his role as supreme gatekeeper. Since he rose to power more than 13 years ago, large and controversial legislative matters — from charter schools, to the death penalty, to sexual predator laws — have tended to hinge on his opinion and that of his conference members.

While he brushed off the label of obstructionist, Mr. Silver has been more careful about leaving himself isolated on the issue of congestion pricing. He has expressed tentative support for the idea of fees and has been careful to note that his members — not him — have final say.

“Shelly doesn’t want to be the guys who always says no,” a New York City lobbyist said. “He doesn’t want to be known as the guy who always kills things.”

Messrs. Bloomberg and Silver have had a relationship that many say is based on mutual toleration. With few exceptions over the years, they have adhered to a code of decorum. Rarely have they attacked each other personally, instead preferring to limit airings of resentment and frustration to private settings.

The last time the two city leaders lost their tempers with each other was when Mr. Silver almost three years ago defeated plans to build a stadium on Manhattan’s West Side. Mr. Silver argued that the stadium project would detract from business development in his Lower Manhattan district. Mr. Bloomberg blamed him for depriving the city of a convention center and the opportunity to host the 2012 Olympics.

After having assiduously courted Mr. Silver, the mayor erupted at the speaker, accusing him of negotiating in bad faith and of carrying on a charade. Mr. Silver, in turn, told the Times that his relationship with the mayor was dead.

Months later, the mayor was reelected, and, faced with the prospect of having to work with the speaker for four more years, seemed to bury the hatchet.

In public forums, the mayor now talks about the speaker as if the scorched-earth confrontation over the stadium were a vaguely recalled difference in opinion. Mr. Bloomberg has recently praised Mr. Silver as a civic partner, a force for good.

“I have given enormous amount of credit to Shelly Silver who has in the end been there for most of the things the city needs,” Mr. Bloomberg said two weeks ago.

With the fate of congestion pricing in Albany’s hands and with the Republican-controlled Senate signaling support for the plan, the Assembly and Mr. Silver are now in a position to extinguish the signature initiative of the mayor’s second term.

Yesterday, Assembly Democrats spent hours debating congestion pricing at a private conference meeting, with lawmakers taking turns airing their opinion. They are expected to resume the debate today and decide whether to bring the plan to the floor for a vote.

The New York City Council approved a congestion-pricing plan this week after months of complex negotiation between city lawmakers and Mr. Bloomberg. The mayor has agreed to endorse some members who voted for the plan. Some received promises of public transportation improvements and other benefits for their districts.

The top concerns raised by state lawmakers at the conference was that pricing fee would be felt more deeply by middle-class motorists than wealthier drivers and that it would do little to reduce traffic.

Bloomberg officials, who came to Albany yesterday to pitch their plan one more time, said they were not considering any response to a rejection by the Assembly.

“The plan is to focus on the vote now. That’s plan A, B, and C,” the commissioner of the New York City department of transportation, Janette Sadik-Khan, said.