Though Mayor Bloomberg won a unanimous vote from the Metropolitan Transportation Authority’s board for a New York Jets stadium on the far West Side, the victory may be short-lived. As he wades into his re-election campaign, he will have to explain to voters why, less than two months ago, he had sought quick approval of a deal to sell the Jets the right to develop the 13-acre riverfront site at what proved to be a fraction of market value.

The football team originally offered the MTA $100 million for the right to build a domed stadium over the Hudson rail yards. The mayor portrayed the offer as a bargain, given that the area had long lain fallow and the site, which could not be developed until a mammoth platform is built over the operating rail yards, was a difficult one to build on. Real estate experts, however, said the Jets had offered a lowball bid. The MTA sought $300 million, and some industry sources said the development rights were worth more in the neighborhood of $900 million – about $200 a square foot – and urged the MTA to put the project out to bid. In early February, the owners of Madison Square Garden, a Cablevision subsidiary vigorously opposed to the construction of a large sports facility that could offer daunting competition, offered an alternate plan to develop housing and retail space along the river. Their bid, initially valued at $600 million, forced the Jets to up the ante. The bid they submitted last month could bring the MTA $720 million.

The battle may end up haunting Mr. Bloomberg as he seeks re-election.

In a rare instance of apparent unity between the city’s leading Democrats and conservative Republicans, candidates seeking Mr. Bloomberg’s job cried foul yesterday, questioning why the Jets were getting what they term a sweetheart deal to build a new stadium.

“This might be the worst land deal since Manhattan Island was sold for 24 bucks,” the speaker of the City Council, Gifford Miller, who is one of those candidates, told reporters on the steps of City Hall yesterday after the vote. “This is not over, not by a long shot.”

His Democratic rivals – Fernando Ferrer, Rep. Anthony Weiner, and C. Virginia Fields – have all accused Mr. Bloomberg of seeking to force upon the city his plan for a New York Sports and Convention Center at Manhattan.

A Republican who is seeking to challenge the mayor in a primary this fall, Thomas Ognibene, told The New York Sun: “The crucial issue here is that Mayor Bloomberg was willing to let this site go for at least $600 million less than fair market value, and I intend to remind people of that during the campaign. We need to look at some of the other venues around the city they are planning for the Olympics. I bet the West Side stadium is just the tip of the iceberg.”

Political analysts said that while the father and son who run Cablevision, Charles and James Dolan, may have been motivated by economic self-interest, in the end they did New Yorkers a favor by forcing up the price of development rights on the West Side. The MTA will probably end up with hundreds of millions of dollars more than it might otherwise have had.

“We should get the city’s straphangers to all give a dollar to reimburse the Dolans for the $20 million they spent on opposing the stadium,” a Baruch College professor of political science, Douglas Muzzio, said. “The $100 million offer to the Jets could be a liability for Bloomberg in the campaign and it could get some traction – unless, of course, the stadium really gets going or New York gets the Olympics. Then I think the issue will start to fade.”

Mr. Bloomberg’s steady advocacy of the West Side stadium, however, has started to win over New Yorkers, according to a Quinnipiac University poll released this week. Opposition to the stadium dropped to 49%, from 56% earlier this month, after the announcement that the stadium could be the venue for the 2010 Super Bowl.

“The Super Bowl gives him a few more yards,” the director of the Quinnipiac University Polling Institute, Maurice Carroll, said of the mayor. “But it doesn’t put him in the end zone.”

Getting to the goal line, according to a 1997 mayoral candidate, Ruth Messenger, might not be easy. “A substantial part of the public doesn’t want a stadium, the former Manhattan borough president told the Sun yesterday. “An objective look at this says this probably wasn’t the best deal for the public-transit system. The question really is how will the public perceives the mayor’s focus on this. He may get some respect for being skilled enough to get something through, but they may not like that that is what he is spending his time on.”

The Quinnipiac Poll, which interviewed 1,371 New York City registered voters between March 21 and 28, found they were split on whether Mr. Bloomberg’s stadium advocacy showed leadership or arrogance. The poll’s most important number for Mr. Bloomberg may be that 68% said the stadium would not affect their vote come November.