Madison Square Garden’s offer of $600 million for the right to build a mostly residential complex over the West Side rail yards unlocked the possibility of an open bidding process for the 14-acre parcel. Even though the land offers magnificent views from the only remaining undeveloped parcel on Manhattan’s Hudson waterfront, however, real estate experts doubt that it would produce a bidding war with combatants other than the owner of the Jets, who wants to build a sports stadium on the site, and the owners of Madison Square Garden, who want to thwart those plans to preserve the Garden’s status as Manhattan’s largest venue for sports and entertainment events.

Should the Metropolitan Transportation Authority’s rail yards be opened to development other than for a Jets football stadium, the experts said, then the extension of the no. 7 subway line would not be built. Further, because of environmental concerns about building over a working rail yard and questions about the platform that will be required, the development of residential units may not generate more than the $100 million the Jets have offered for the air rights, let alone the net $350 million offered by the Garden to build “a mixed-use community centered around residential housing,” some developers argue.

Building residential towers over working rail yards could pose risks of oil or gas leaks, or fumes, and other environmental problems, experts said. Residential buildings have the highest environmental safety standards, and the resulting expenses, plus the need for costly liability insurance in the event a resident or MTA worker should be sickened or injured, could offset the benefits of the prime waterfront location, some developers said.

“We would be perfectly interested in bidding for property over the rail yards, but if land in the Hudson Yards, where you don’t have the platform issue or environmental questions, is going for $100 a square foot, I would think the MTA site would sell for less,” a large developer who owns parcels in Hudson Yards, which the City Council recently rezoned for residential development, said. The MTA rail yards is part of the Hudson Yards neighborhood.

“To make it worth our while,” the developer said, “they would have to give us enough air rights so we could cover these costs and make a profit.”

That would mean a very large number of apartment units.

“Because of these costs, it is not at all obvious in my mind that through an open bidding process the MTA will necessarily get more money,” the developer concluded.

Others said the benefit of the waterfront parcel would offset any unseen costs.

“Waterfront views mean double the price,” the president of the nonprofit planning group Regional Plan Association, Robert Yaro, said. “This is the only block of waterfront that is not yet spoken for between Spuyten Duyvil and the Battery.” The association has opposed the stadium plan. The rail yards land is also an unusually large undivided piece of developable land.

If the Jets’ plan to build the New York Sports and Convention Center, as it is known, is scuttled, it is unlikely the No. 7, a subway line that runs from Flushing, Queens, to Times Square, will be extended west, the experts said.

Speaking of Mayor Bloomberg’s deputy mayor for economic development, Daniel Doctoroff, a senior fellow at the conservative think tank Manhattan Institute, Julia Vitullo Martin, said: “What Doctoroff did is something very smart. He made artificial deadlines to get things done, such as the arrival of the Olympics committee to spur the process along. Artificial deadlines are how you get things done in the city. Without this, do I think the No. 7 will get done? No.” Ms. Martin supports the stadium plan.

Without the extension of the no. 7 line, there would be no major public transportation in the neighborhood, lessening the likelihood of commercial development.

“Housing can happen without the no. 7 train, but not office space,” the developer said.

And the Regional Plan Association’s Mr. Yaro acknowledged: “It will be residential in the area because, at least for now, there will be no No. 7 extension.”

Another potential obstacle to residential development at the rail yards is the rezoning and planning process, which could take between two and three years.

“First you have to decide on a plan for the site, and the city, the community board, the RPA are all going to squabble over what should be there,” the developer said. “After you come up with a plan, which will take a year, there is the two-year planning process.”

“Building residential will mean a new environmental impact statement and a rezoning, which will take three years, and only then will the MTA get their money. That is a terrible idea,” the president of the Real Estate Board of New York, Steven Spinola, said. REBNY, as the developers’ lobbying group is known, has supported the Jets’ plan.

Mr. Yaro disagreed. “This is state owned property, and the Empire State Development Corporation can override zoning, so there is no need for the two-year planning process,” he said. “All they would have to do is a request for proposals, and then start building.” The MTA is a state authority, and Empire State is the state’s development arm.

“Deciding on a plan for the site would also move much quicker than normal because the community board, the borough president, and real-estate developers are all on the same side,” Mr. Yaro said.

A key member of Community Board 4, which represents the area of the rail yards, made a similar point. “No new environmental impact statement is needed,” the chairwoman of Board 4’s land-use committee, Anna Levin, said. The board opposes the stadium plan.

Ms. Levin said the impact statement that has already been done for the Jets’ plan considered a residential alternative for the site, known as “Alternative O.”

“It is not another three-year process because a lot of the baseline work has already been done,” she said.

The Bloomberg administration is pushing for an early decision by the MTA to sell the air rights to the Jets. The MTA and the Jets tentatively agreed to nonbinding arbitration by a former Senate majority leader, George Mitchell, the Disney Co. chairman, but the MTA board has yet to approve the move. Meanwhile, Madison Square Garden released some details of its offer late Friday, saying it had begun assembling architects and engineers and was looking for a development partner to make final its strategy for the property.