ALBANY – Two key lawmakers cast serious doubts yesterday on New York City’s chances of winning the 2012 Olympics, adding to what could be an imminent political nightmare for the Bloomberg administration by saying they are reluctant to authorize a new venue for the games until after a decision on the host city is made.

The Republican leader of the Senate, Joseph Bruno, and the Democratic speaker of the Assembly, Sheldon Silver, have the power to block the proposed $2-billion sports complex and convention center on Manhattan’s far West Side. The two men have appeared to think out loud on the issue for weeks, even as opponents of the proposed 75,000-seat domed stadium provide one reason after another to delay its construction.

Officials of the New York Jets, who were awarded development rights to build the stadium over the Metropolitan Transportation Authority’s West Side rail yards, have lobbied lawmakers in Albany this week to act soon on the project. The team brought the hero of the 1969 Super Bowl, Joe Namath, and an African-American activist, the Reverend Alford Sharpton, to the state Capitol in hopes of accelerating a vote that would free up a $300 million state subsidy. The city has pledged a similar subsidy.

Those efforts appeared to have failed, however, as the two legislative leaders, throughout the day, leveled criticism at the project.

Mayor Bloomberg, who faces re-election this fall, has said that if New York City is to remain in contention for the 2012 Summer Games, the stadium must be approved before the International Olympic Committee chooses the host city on July 6. The comments by Messrs. Bruno and Silver should dim the mayor’s hopes for legislative cooperation, even as the City Council is expected to pass a measure today to block the mayor’s plan for financing the city’s $300 million portion of the project: the construction of the platform on which the stadium would be built.

The Bloomberg administration repeated its deadline yesterday, setting up a dramatic showdown with Messrs. Bruno and Silver over a project first proposed as a centerpiece for the Olympic bid four years ago.

“We are not going to speak for what the strategy of others may be,” a spokesman for the city’s bid committee, Lazaro Benitez, said. “But I say this emphatically: If the stadium is not in place before the vote, then we do not get the Olympic games.”

The swarm of doubts that now circle the stadium threatens to expose Mr. Bloomberg to even stiffer criticism for his handling of development in Lower Manhattan.

Mr. Silver, whose Manhattan district includes the World Trade Center site, criticized Mr. Bloomberg and Governor Pataki for focusing on the proposed West Side stadium at the expense of Lower Manhattan, even before the governor conceded last week that security concerns would delay redevelopment there by at least several months.

The appearance of Rev. Sharpton at the Capitol reflected the pressure that several minority-group members of the Assembly are putting on Mr. Silver to approve the stadium, on the grounds that it would create thousands of jobs for constituents. Rev. Sharpton said his support is based on job creation, not the Olympics.

“I would love to see the Olympics,” Mr. Sharpton said. “But I would support the stadium, Olympics or no Olympics.”

Despite the pressure, Messrs. Bruno and Silver appeared to endorse a strategy that, if followed, would almost certainly extinguish New York’s Olympic chances and could keep the stadium project itself from going forward.

Mr. Silver said lawsuits connected with the stadium should be resolved before a vote is taken. Legal challenges to the project stem from a contention that the MTA did not get top dollar from the Jets for air rights at the yards. A state Supreme Court judge handling the suits expects to rule by June 2, though a pro-MTA, pro-Jets decision would almost certainly be appealed.

Mr. Bruno went further than Mr. Silver, suggesting that a state decision on the project could wait until after the July 6 vote in Singapore.

“I have said to the mayor, and repeatedly,” Mr. Bruno said, “we will do whatever it takes to accommodate the Olympics if they make a positive decision, and I hope they do, to come to New York City.”

Messrs. Bruno and Silver have emerged as central players in the stadium battle because they control two of the three votes on the Public Authorities Control Board, a board established, in part, to approve the disposition of assets held by public authorities. A 3-0 vote would be needed for the project to proceed.

Mr. Pataki, who controls the third vote on the board, is a strong supporter of the stadium. He also sets the agenda for the board’s monthly meetings. An aide to the governor said a vote on the stadium is scheduled for the group’s May meeting, next Wednesday. Board members are permitted to table a single item once each, leaving open the possibility that Messrs. Bruno and Silver could postpone scheduled votes next week and next month.

If they did, Mr. Pataki would have to convene an emergency meeting of the board for stadium authorization to take place before July 6.

Mr. Bruno acknowledged for the first time yesterday that he would look for something upstate in exchange for authorization of the stadium – even as he sought to deny he was doing so.

“Whatever we end up doing in the city, there ought to be equity and there ought to be balance, because what happens on the Island is critically important, what happens in Buffalo, Rochester, Syracuse, and Albany is important. So we’re going to look for offsets for what we invest in the city,” the Republican leader said. “But are we holding up the stadium waiting for an offset? Absolutely no.”

Mr. Silver suggested that an online ranking yesterday of potential Olympic hosts had made him even less eager to bless the stadium.

The BidIndex ranking, posted on the Web sitewww.gamesbids.com, purports to predict a city’s chances of success based on mathematical modeling. among other factors.

The site said Paris is now the most likely of the five finalists to win the games, with New York City falling to fourth place. Mr. Silver also repeated his concern that the development of commercial office space near the stadium, a part of the vision for the far West Side that Mr. Bloomberg and his Deputy Mayor Daniel Doctoroff have embraced, would make it even harder to find tenants for Lower Manhattan.

“My serious concern is the 24 million square feet of office space when you can see that we are struggling with office space downtown, that there are no leases out for a building that is almost completed, one that is in some semblance of the planning stages, and there are no leases outstanding, and we are now going to add 24 million square feet of competition,” Mr. Silver said. “At this point, that doesn’t make sense to me.”

Although Mr. Silver again said that he wants the lawsuits resolved before acting on the stadium, the chairwoman of the Assembly committee on labor, Susan John, a Democrat of Monroe County in western New York, differed on that point.

“I don’t believe that the lawsuits of necessity mean that the vote cannot be taken,” Ms. John said. “The vote can be taken and the legal issues may very well change the outcome of what’s done, but I believe it’s in our interests to move forward.”