Suburban pols are demanding they get a cut of congestion pricing cash meant to rescue the subways — even though city taxpayers already underwrite the commuter railroads.

The Long Island Railroad and Metro-North got 37 percent of the MTA’s construction budget over the last decade, despite the suburbs only accounting for 28 percent of the agency’s tax and fare revenues.

The disparity amounts to $4.5 billion, a Post analysis found.

That’s enough to replace the subway’s crumbling, century-old signals with the MTA’s new computerized system on 56 miles of subway, upgrading virtually every major line in Manhattan.

The Post calculated it costs roughly $80 million per mile to install the new signals after the MTA refused to provide a figure.

“[The subway] is the lifeblood of the city and state’s economy and tax base,” said Riders Alliance spokesman Danny Pearlstein. “It is suffering following decades of disinvestment and desperately needs to be modernized.”

All told, the MTA allocated $50.9 billion for subway, bus and commuter railroad projects between 2010-2019, not counting Hurricane Sandy repairs, according to data from the Citizens Budget Commission. More than half, $29.8 billion, came in the last five years.

The MTA claimed the analysis was off base because funding for construction projects can come from myriad sources.

“The Post is comparing apples and oranges in a deeply misleading way,” said MTA external affairs director Maxwell Young.

The Senate Democrats remain supportive of the congestion pricing concept, a spokesman said.

The Post examination comes as Gov. Andrew Cuomo and Mayor Bill de Blasio lobby lawmakers to sign off on an MTA funding plan that hopes to generate $22 billion in new money for subway repairs.

The bulk would come from charging a fee to vehicles entering Manhattan below 61st Street.

Within days of the congestion pricing rollout, Long Island and Hudson Valley state Senate delegations put out their hands for a piece of the pie for their constituents.

“As the representatives for millions of Long Island commuters, it is our responsibility to ensure that any congestion pricing plan is not funded on their backs without substantial benefit,” wrote state Sens. John Brooks, Jim Gaughran, Anna Kaplan, Todd Kaminsky, Monica Martinez, and Kevin Thomas. The statement was also signed by the Senate majority leader, Westchester’s Andrea Stewart-Cousins.

But, some of the MTA’s highest profile projects in recent years have benefited suburban commuters.

That list of projects includes the MTA’s biggest money draw: the long-overdue project to build a LIRR connection to Grand Central Terminal. The project was originally supposed to cost just $4.3 billion. But it grew to $7.3 billion by 2009 and is now $11.2 billion.

The new station will serve just 162,000 people daily, a fraction of the 3 million people who swipe a MetroCard in Manhattan.

“East Side Access is the money pit that sank the subways,” said John Kaehny, of the good government group Reinvent Albany. “[It] screwed commuters and straphangers, depriving the subways of needed signals replacement and maintenance.”