There’s an untapped pot of government funds worth billions that could be used to shore up the subways, according to a liberal ex-Democratic lawmaker and a conservative government watchdog.

They have joined forces to urge Gov. Cuomo and legislative leaders to redirect unspent bank settlement funds to help fund badly needed subway repairs as well as highway and bridge work.

Former liberal Westchester state Assemblyman Richard Brodsky and the Empire Center’s E.J. McMahon said at least $5 billion in bank settlement money is waiting to be spent.

“We suggest that you consider reprogramming and appropriating at least $4 billion of this money for an ‘Emergency Repair and Maintenance Program,’ divided between needed New York City transit upgrades and highway and bridge capital needs in the rest of the state,” they said in a joint letter to Cuomo, Assembly Speaker Carl Heastie and Senate Majority Leader John Flanagan as well as to the MTA board.

“It is essential that such a program be focused on bringing these systems to a ‘State of Good Repair.”

McMahon, research director of the Empire Center for Public Policy, proposed spending the windfall on transportation capital projects in a Post op-ed article on Tuesday.

Billions in bank settlement funds have been earmarked for upstate economic development revitalization projects, the new Tappan Zee Bridge construction, affordable housing, high-speed broad Internet access, health care facilities, security and readiness programs, among other projects.

New York State has received nearly $10 billion in fines and penalties paid by more than 30 banks and financial institutions for violating various state and federal laws.

Many of the settlements were reached following probes by the state Department of Financial Services.

Cuomo did not endorse the proposal.

“As the Governor previously said, the current state of the system is unacceptable and New Yorkers deserve better. Joe Lhota is a proven manager and the state will provide the MTA with the support it needs to address the fundamental issues plaguing the system,” said Cuomo spokeswoman Dani Lever.