If Mayor Bloomberg wants to realize his long-standing dream of developing Manhattan’s far West Side, he may have to go so far as to win the governorship in 2010.

Yesterday, the chances that Mr. Bloomberg will finish his second term in City Hall with construction under way on the 26-acre Hudson rail yards site were reduced, as a tentative agreement between the Metropolitan Transportation Authority and the selected developer, Tishman Speyer, collapsed.

“I am disappointed a deal could not be made with Tishman Speyer to develop the Hudson Yards,” Mr. Bloomberg said yesterday in a statement. “This site represents one of New York City’s best opportunities.”

Since 2002, the Bloomberg administration had been the driving force behind the idea of developing the far West Side, but ultimately it handed over much of the control to the MTA, which owns the rail yards. Mr. Bloomberg would have increased oversight of the MTA if he were elected governor, an office he is rumored to be considering. He has repeatedly denied his interest in running for governor.

There is skepticism among members of the development community that the MTA would be able to resolve the issues that ultimately caused its deal with Tishman Speyer to collapse.

“Right now, the developers are looking at this and guessing why Tishman Speyer made the decision that they made,” the president of the Real Estate Board of New York, Steven Spinola, said. “What is going through their mind is whether they can live with something less than what Tishman was asking for, and what is going through the MTA’s mind is: ‘We just lost Tishman Speyer. What do we have to do to make a deal with one of the other reputable developers?’ Even though they couldn’t with Tishman.”

The MTA said it is re-entering negotiations with “other developers.” Other bidders that answered the MTA’s request for proposals include a joint venture of the Durst Organization and Vornado Realty Trust, Extell Development, and the Related Cos.

“It’s an exciting and important project for New York City and we would be interested in resuming discussions on its development,” a spokesman for the Durst Organization, Jordan Barowitz, said yesterday in a statement. Durst and Vornado Realty Trust bid about $112 million less than Tishman Speyer did.

During the past few days, Mr. Bloomberg tried to salvage the deal, which had been unraveling over the last month and reached the brink of collapse Thursday. Tishman Speyer had been seeking guarantees on the extension of the no. 7 subway line and assurances that the city would approve the rezoning of the western half of the rail yards without major changes. The eastern section of the rail yards has already been rezoned, but the western half still needs to be approved through the city’s land use review process.

Mr. Bloomberg met with the co-founder and chief executive officer of Tishman Speyer, Jerry Speyer, and made assurances that the city would live up to its obligations and get the subway extension completed, and even pledged that the city would guarantee the necessary funding in the event of cost overruns for the no. 7 line, according to a source with knowledge of the discussions.