The Bloomberg administration has touted its $2.4 billion commitment to transportation as the largest contribution to the Metropolitan Transportation Authority since the capital plan to rebuild the subways was introduced in 1982.

But the cornerstone of that commitment, a $2 billion plan to finance construction of a two-track, 7,000-foot extension of the no. 7 line from Times Square to Eleventh Avenue and 34th Street, appears far from certain.

For the five-year, $21.1 billion capital program of the MTA to go into effect, a state review board must vote to approve it by tomorrow. If the Capital Program Review Board, a four-person panel that includes representatives of Governor Pataki; Mayor Bloomberg; the Assembly speaker, Sheldon Silver; and the Senate majority leader, Joseph Bruno, does not approve the plan unanimously, they will send it back to the MTA for changes.

And just as Mr. Silver, along with Mr. Bruno, killed the mayor’s dream of an Olympic stadium on the far West Side, his representative on the board, Assemblywoman Catherine Nolan, could deny approval of the no. 7 extension to that neighborhood.

Yesterday, Mr. Silver said the same problem he had with the stadium plagues the building of the no. 7: commercial development on the far West Side that he fears would compete with the redevelopment of Lower Manhattan.

For the city to pay for the $2 billion extension, the Bloomberg administration has created the Hudson Yards Infrastructure Corporation, which would float $3 billion worth of bonds to finance the extension and related upgrades. That debt would be paid off by development. Mr. Silver fears the debt will give the area the impetus to develop faster than Lower Manhattan. The no. 7 extension “puts on pressure to provide the incentives to build that [area] as quickly as possible,” Mr. Silver said, “and that’s the nature of the objection.” Until that development takes place, the city will pay $989 million over five years to cover the debt service – a plan the City Council has approved.

Yesterday, Mr. Silver said he would prefer a financing scheme that did not finance the extension through rapid development of the far West Side.

Mr. Silver’s comments set up another showdown between the Assembly leader and the Bloomberg administration. Deputy Mayor Daniel Doctoroff said the council-approved plan would not be changed. “There’s no reason for a new plan,” Mr. Doctoroff said.

Whether that puts the extension of the no. 7 in jeopardy will not be certain until the board votes on the capital plan. Though only a small fraction of the budget to be approved in Albany is earmarked for the no. 7, the MTA would be responsible if the cost of the extension exceeded $2 billion, a spokesman for the agency, Tom Kelly, said. Already the estimated price tag is $2.1 billion, making the project a financial matter for the Capital Program Review Board.

Without the $2 billion contribution to the no. 7 line, Mr. Bloomberg will run for re-election with a much-diminished record on mass transit.

Aside from the mayor’s offer to build the no. 7, the city plans to contribute $400 million to the MTA’s capital plan, of which $60 million has been earmarked for preliminary planning and design for the no. 7 in 2005, according to the Independent Budget Office.

That leaves an annual average of about $68 million in direct contributions to the MTA’s five-year capital plan. That would be $25 million less than the annual average amount for the past four years, and significantly less than average contributions under previous administrations, according to the Independent Budget Office.

Inflation has likewise devalued the city’s direct contribution to New York City Transit’s operating budget, which Mayor Giuliani first froze in 1995 at $158 million annually – an amount Mr. Bloomberg would have to raise to $205 million to keep up with inflation, according the Fiscal Policy Institute.

“If the no. 7 doesn’t happen, the mayor is missing in action when it comes to mass transit,” an economist with the Fiscal Policy Institute, James Parrot, said. “Even with the no. 7 it’s not an unprecedented level of commitment.”

Critics of the mayor – including the rider-advocacy group the Straphangers Campaign and the Regional Plan Association – said that rather than pushing the no. 7 extension, Mr. Bloomberg’s legacy would be better assured by committing that money to what they consider to be the subway system’s more urgent needs.

“The bigger issue is the city’s direct contribution to the maintenance and upkeep of the MTA, that needs to come first,” a spokesman for the Regional Plan Association, Jeremy Soffin, said. “The only focus should not be the West Side. We’d like to see that sort of wholehearted support and energy put toward MTA priorities such as the Second Avenue subway and East Side Access.”

The modern heyday for municipal investment in mass transit was between 1982 and 1995, when the city gave about $138 million a year to the MTA’s capital program to be used by New York City Transit, the subsidiary in charge of the subways and buses. Money appropriated from other sources, including federal funding, swelled that to an average of $231 million annually, according to the city’s Independent Budget Office.

Beginning in 1996, under the Giuliani administration those contributions began to fall precipitously. For the 2000-04 Capital Plan, the city contributed around $93 million a year – a figure that does not include money received by the MTA but funneled through the city from the sale of the New York Coliseum for $345 million to Related Properties in 1999. That site is now occupied by the Time Warner Center.

The chairman of the state Assembly’s Committee on Corporations, Authorities and Commissions, Richard Brodsky, bemoaned the diminution of city financing, although the state has the legal authority to force the city to increase its share.

“Legally we can ask city to pay more, we have the constitutionality to mandate this stuff,” the Westchester Democrat said. “But we try not to do it.”