Northeast states and transit agencies - including SEPTA and NJ Transit - are being asked to pay more to maintain the heavily traveled rail corridor between Washington and Boston that they share with Amtrak.

The new cost-sharing plan for the Northeast Corridor is due to take effect Oct. 1, although Massachusetts has objected. That state is upset about its higher bill and the prospect that the plan "may mark the beginning of a devolution of federal responsibility down to the states."

The states, transit agencies, and Amtrak are struggling to balance the costs of the 457-mile corridor that carries 710,000 commuter-rail and 40,000 Amtrak passengers on more than 2,000 trains each day.

In addition, state-supported feeder routes, such as the Keystone Corridor linking Pittsburgh, Harrisburg and Philadelphia, are connected to the NEC and carry thousands of additional riders.

Congress in 2008 ordered Amtrak, which owns most of the NEC, and the other corridor users to devise a formula for sharing costs that historically have been divvied up in more than 50 separate contracts.

"There hasn't been any uniformity to how those costs are shared. Some are overpaying and some are underpaying," said Toby Fauver, a Pennsylvania deputy secretary of transportation who co-chaired the committee that created the new cost-sharing plan.

The committee is part of the Northeast Corridor Infrastructure and Operations Advisory Commission. The commission is composed of one member from each of the NEC states (Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Pennsylvania, Delaware, and Maryland) and the District of Columbia, four members from Amtrak, and five members from the U.S. Department of Transportation.

In December, the commission voted, 17-1, to approve a new cost-sharing policy, designed to spread the burden for spending $425 million a year for the next three years for maintenance and upgrades on the corridor. Then the cost would rise to $530 million a year.

The NEC Commission has no way to compel the states to pay more; disputes could be taken to the federal Surface Transportation Board. However, the lopsided support for the new policy among the commission members indicates that most are prepared to pay up.

For SEPTA, that means its payments to Amtrak would increase from $38.4 million this year to $52 million next year.

"The increased funding contribution requested of SEPTA and other transit authorities is to be used to bring the Northeast Corridor into a state of good repair," SEPTA chief financial officer Rich Burnfield said. "However, given the significant backlog of state-of-good-repair needs, the federal government should also contribute to this effort."

For NJ Transit, the cost would be more than $100 million a year.

Meanwhile, Massachusetts balked at its bill of $32.6 million.

That state, which owns the 38-mile section of the corridor within its borders, said its contribution would just lower other users' costs, rather than actually improve the rail corridor.

And Massachusetts is skeptical that the federal government will uphold its obligation to add $125 million in new funding for the corridor annually for the next three years, then boost its contribution to at least $400 million a year above current levels.

"While the policy obligates the states to these new payments, it does not ensure new or sustained federal funding participation in support of state capital and operating expenditures," wrote David Mohler, a state transportation official who represents Massachusetts on the commission.

"Massachusetts is concerned that the adoption of the interim policy may mark the beginning of a devolution of federal responsibility down to the states."

Massachusetts' fears might be well-founded: The U.S. House approved a proposed budget for Amtrak this month to cut Amtrak's funding by 17 percent, or $242 million.

The corridor's infrastructure improvement needs are expected to cost about $18 billion over the next five years, and only about $7.5 billion is funded under current plans, according to the commission.

"These needs cannot be met without substantial action and investment by the federal government," the commission wrote in its cost-sharing plan.

Despite the first-ever cost-sharing plan by the states and transit agencies, "it has been the longstanding position of NEC stakeholders that the federal government has primary responsibility for eliminating the backlog of deferred maintenance to restore the infrastructure to a state of good repair," the commission said.