TRENTON — Commuters will face "significant outages" during work at New York City's Penn Station this summer, Amtrak officials said Friday, testifying before New Jersey lawmakers about the agency's response to a series of breakdowns at the station over the past month.

But officials didn't yet know how exactly riders will be impacted by the work, which Amtrak CEO Wick Moorman said was necessary to avoid the risk of more "unplanned disruptions." The agency claimed responsibility for two derailments in late March and early April at Penn Station, although it faulted NJ Transit for another April incident that left 1,200 people stranded for hours outside the station.

Nor could Moorman say how Amtrak would manage during the next decade with what officials described as maxed-out capacity at Penn Station, until a new tunnel under the Hudson River could be built.

"That's a great question, and I don't have an answer," Moorman said. Of the station, he said, "All we can do is go in and ensure that it runs as well as it possibly can under these conditions."

The agency's aging infrastructure has faced scrutiny following the derailments, which Moorman said spurred the agency to accelerate the work it plans to do this summer.

Also in the spotlight is NJ Transit, which relies on the Amtrak-operated infrastructure. The state agency has been targeted by frustrated commuters, some of whom have started a social media push asking fellow riders not to pay for May monthly passes.

When delays happen, "we do need to do a much better job ... to get as much information as out as we can," said NJ Transit executive director Steven Santoro, who also testified Friday. The agency is rolling out an app for better notifications, he said.

The agency sometimes doesn't have enough information to tell riders how long their trains are delayed because of "evolving situational awareness," Santoro said. For instance, with the people stuck in the Hudson tunnel for three hours, "we thought that issue would be resolved quickly," he said.

Santoro couldn't say how the upcoming work by Amtrak would affect NJ Transit, which runs 350 trains in and out of Penn Station daily, and whether delays would be sustained equally by both agencies.

Depending on the situation, "we might have to have people on platforms to control crowds," said Santoro, who said NJ Transit received a plan from Amtrak on Friday but had not yet reviewed it.

The planned work — which Moorman said would cause "two to three" outages affecting weekday travel — will not fix the damage incurred during Hurricane Sandy.

That damage will eventually force Amtrak to close one, if not both, of the current tubes under the Hudson River, Moorman said.

While a new tunnel would allow Amtrak to fix the damage, federal funding for a $24 billion plan that would build a new tunnel and replace the existing infrastructure is not guaranteed.

Democrats leading Friday's hearing were quick to fault Gov. Christie for canceling a previous tunnel plan in 2010, arguing a new tunnel could have been ready next year.

"The fact that the governor has the temerity, blaming anyone but himself .... is astounding to me," said Assemblyman John McKeon (D., Morris), chair of the Judiciary Committee.

He accused Christie of "hypocrisy" for attacking Amtrak, citing "underfunding" of NJ Transit and fare increases during the governor's tenure.

The Republican governor, who after the derailments directed NJ Transit to stop paying Amtrak maintenance fees, recently said he had "no regrets" about canceling the ARC tunnel, which he panned in 2010 as a bad deal for taxpayers.

"The project stunk," he said.

At Friday's hearing, Assemblywoman Elizabeth Muoio (D., Mercer) described the issues facing NJ Transit commuters recently as "only the latest in a long line." She noted a Bloomberg report Thursday detailing safety lapses in recent years identified by Federal Railroad Administration inspectors.

Describing the lapses as old, "we've moved past that," Santoro said. But he later acknowledged that the agency is enhancing supervision and hiring employees in response to the federal audit.

"I did not want to leave the impression all of our issues are behind us," he said.