Fares are at risk for an even greater hike if the MTA is forced to borrow billions of dollars to fund its transit improvement plan, the state comptroller warned Tuesday.

Comptroller Tom DiNapoli's report said that the MTA would have to pay out an extra $70 million for every $1 billion it borrows -- the equivalent to a 1% hike in fares and tolls, which are already set to go up 4% every two years starting on 2015.

"Additional borrowing could increase pressure on fares and tolls, and while the MTA should look for opportunities for savings, deep cuts could affect the future reliability of the transit system and jeopardize expansion projects," DiNapoli said in a statement.

The MTA needs to find the money for nearly half of the its $32 billion proposal to fix the transit system over the next five years with new train cars, equipment and repairs to stations. Currently, the MTA anticipates it can bring $16.9 billion to the table, including money from the city and federal government and real estate. The state could contribute as well, but no commitments have been made. .

The MTA borrowed heavily in its last plan from 2010-2014, loading up the agency this year with nearly $35 billion, according to forecasts.

"The MTA network is a $1 trillion asset and is the engine that drives the New York economy," said MTA spokesman Adam Lisberg. "The comptroller's report emphasizes how critical it is for all the MTA's stakeholders to engage in a dialogue about how to fund the capital program to renew, enhance and expand the MTA network."