With a showdown looming in Harrisburg, SEPTA officials made a final pitch Thursday for millions more in state aid to avoid a "devastating" cutback in service.

A House vote is expected as early as next week on statewide transportation funding, and SEPTA says it is prepared to enact a doomsday plan to eliminate nine of its 13 rail lines, close a subway line, and convert all trolley routes to bus lines.

Deputy general manager Jeffrey Knueppel told the SEPTA board that old rail bridges, power stations, vehicles, and train stations could no longer be maintained and must be replaced.

Without more state funding for those capital needs, SEPTA will begin a "rational progression" of cutbacks over a decade, starting next year, Kneuppel said.

"If we can't replenish our assets, we're in trouble," he told the board.

Deteriorating railroad infrastructure, inherited by SEPTA from its bankrupt private predecessors, the Pennsylvania Railroad and the Reading Co., are the biggest drivers of SEPTA's funding gap. So the biggest service cuts would fall on Regional Rail passengers.

The plan calls for suspending service on the lightly traveled Cynwyd rail line next year, the heavily traveled Media-Elwyn line in 2015, the Chestnut Hill West line in 2018, and the West Trenton, Airport, Warminster, Marcus Hook-Wilmington, Fox Chase, and Chestnut Hill East lines in 2023.

In addition, SEPTA says it would truncate its busiest line, Paoli-Thorndale, at Malvern in 2023, and end service to Doylestown on the Lansdale-Doylestown line in 2018.

Also, the plan calls for retiring - but not replacing - 284 railcars, leaving the agency with just its 120 Silverliner V cars by 2023.

The doomsday plan also calls for converting trolley Routes 10 and 15, which serve West Philadelphia and North Philadelphia, to bus lines next year and doing the same in 2018 with trolley Routes 11, 13, 34, and 36.

The plan would close the lightly traveled Broad-Ridge Spur subway line in 2018 and end all express service on the Broad Street subway by 2023.

SEPTA's $304 million annual capital budget, fueled with state and federal money, is much smaller than the budgets of transit agencies in Boston ($815 million), Washington ($997 million), New Jersey ($1.2 billion), and Chicago ($957 million).

SEPTA needs to spend about $650 million a year for 10 years to rebuild and replace its bridges, vehicles, stations, and tunnels, SEPTA officials said.

General manager Joseph Casey said states including Ohio, Maryland, Virginia, and Massachusetts all came up with major transportation funding increases this year, and he said Pennsylvania needs to follow suit.

SEPTA is lobbying House lawmakers to pass a Senate-approved plan to increase transportation funding by $2.5 billion annually for highways, bridges, and public transit. That would mean about $400 million more a year for SEPTA.

The House recessed July 1 without voting on a transportation-funding measure amid wrangling over how much to provide for public transit, how much to increase gas taxes and motorist fees, and efforts to tie transportation to a push to privatize the state liquor business.

Having returned this week to Harrisburg, House Republican leaders indicated they might bring the Senate bill to the floor in the next week or two, SEPTA officials said.

"We're at the end of the struggle," said SEPTA board chairman Pasquale T. "Pat" Deon Sr. "We can't do more with less."