A new federal transportation funding plan could cripple SEPTA's ability to buy vehicles or rebuild stations, general manager Joseph Casey said Wednesday.

Casey joined executives from the nation's largest transit agencies to oppose the funding bill being pushed by Republican leaders in the House because the bill eliminates dedicated funds for mass transit and gives it to highway projects.

"It would be devastating to Philadelphia," Casey said.

Currently, 2.86 cents of the 18.4 cents-per-gallon federal gas tax goes to buses, subways, and commuter rail lines. Eliminating that dedicated source of funds and replacing it with a one-time transfer of funds, as the GOP plan proposes, would leave transit programs vulnerable in future budget fights as Congress looks to reduce overall spending.

SEPTA gets about $235 million a year in federal funding, most used for the agency's $300 million-a-year capital budget, which pays for new buses, rail cars, and construction such as station improvements and bridge replacements.

The House transportation funding bill, which would provide $260 billion over five years, has drawn fire from both ends of the political spectrum, and House GOP leaders delayed a vote on the measure this month because they were not certain it would be approved.

Floor votes are likely next week in the House.

A separate proposal in the Senate would provide $109 billion over two years for funding transportation projects and would not eliminate the gas-tax revenue for mass transit.

Congress has been struggling to come up with a transportation spending plan since the last six-year law expired in 2009. Congress has since passed a series of temporary funding bills, and the current one expires on March 31.

Federal Transit Administrator Peter Rogoff said Wednesday that "the House majority's approach eliminates a guaranteed funding source for mass transit that has been in place since the Reagan administration."

Wednesday, transit agency leaders, including SEPTA's Casey, joined in a nationwide conference call with reporters to decry the House bill. They said it would mean service cuts and fare hikes at many agencies.

Casey was joined by chief executives from transit agencies in New York City, Chicago and Washington, among others.

Major SEPTA projects, like the long-delayed $100 million City Hall subway station renovation, cannot be done if there is no dependable source of funding, Casey said.

"How do you plan for that without knowing if you're going to get the money?" Casey said.

And he warned that borrowing would get more expensive for SEPTA and other transit agencies. He said SEPTA's financial consultant said an end to federal gas-tax revenues would probably mean a two-level downgrade in SEPTA's bond rating, which would increase its borrowing costs by millions of dollars.

State funding for transportation is also bogged down, with Gov. Corbett delaying action on recommendations to pay to fix crumbling highways, bridges and transit systems.

"If they take away federal funding, I will have no federal, state or local source to support long-range funding," said Richard Burnfield, SEPTA's chief financial officer.

The transit leaders said they supported a bipartisan effort by some Northeastern and Midwestern representatives to restore the gas-tax revenues to mass transit. The sponsors of the Nadler-LaTourette amendment include Rep. Mike Fitzpatrick, a Bucks County Republican.

Contact staff writer Paul Nussbaum at 215-854-4587 or pnussbaum@phillynews.com.