The head of Amtrak admitted Thursday that the agency had advance warning of the track problem that caused an NJ Transit train to derail Monday at Penn Station, but didn’t act on it.

The Long Island Rail Road said its service into and and out of the Penn would be normal Friday morning, if Amtrak successfully completed track repairs at the Manhattan rail hub, the busiest in the nation.

“I’ll believe it when I see it,” said LIRR commuter Jennifer Reilly, 53, who left two hours early from her Manhattan job as a university fundraiser to catch a train at Penn.

At a morning news conference in the station, a contrite Amtrak president and executive officer Charles ‘‘Wick’’ Moorman admitted that the railroad ‘‘got it wrong” in failing to address the track problem before the derailment. His mea culpa came on the fourth consecutive day filled with cancellations and delays for many of the 230,000 LIRR commuters who pass through Penn Station daily.

Moorman acknowledged that problems in Penn’s tracks, owned and maintained by Amtrak, were behind Monday’s derailment and another less than two weeks ago.

“In this instance we disappointed our customers. We understand that and we take responsibility for it,” Moorman said at Penn. “And we’re committed to making sure it doesn’t happen again.”

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Moorman said weakened “timbers” — wooden rail ties that support the steel rails on top of them — were to blame for Monday’s derailment at century-old Penn. Amtrak officials had been aware of the problem with the ties at that location, which had been inspected just “a few days” before the derailment, he said.

“We clearly did not have the understanding that there was an imminent failure,” Moorman said. “We knew that at some point this year in our maintenance program we would be getting to it. Clearly, that is something where we got it wrong.”

The compromised wooden beams allowed trains to widen the gauge of the rails, so when an NJ Transit train pulled into Track 9 at Penn on Monday, it “shoved the rails apart,” causing the train’s wheels to fall off of them, he said.

The Federal Railroad Administration, which oversees railway safety, requires that every 39-foot section of rails have “a sufficient number of crossties that in combination provide effective support that will” maintain the track gauge.

Robert Halstead, a Syracuse-based railroad accident reconstruction expert and investigator, said although some railroads use concrete rail ties, less expensive wooden ties are still widely used throughout the industry and can last 40 years or more. But once a series of ties become so rotted that they can no longer hold the spikes or bolts that secure rails to them, they “need to be replaced — no question.”

Moorman said the cause of the March 24 derailment of an Amtrak Acela train at Penn was “mismatched” pieces of rail that allowed the train’s wheels to climb onto the rail.

“That sounds like pretty shoddy maintenance,” Halstead said.

The Long Island Rail Road Commuter Council — the official watchdog of the LIRR, Penn Station’s primary tenant — in a statement Thursday said it was “alarmed” by the pattern of deferred maintenance described by Moorman, and demanded “corrective actions be taken as rapidly as possible.”

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”Defects like those that led to the two recent Penn Station derailments directly threaten the lives, safety and careers of Long Island commuters,” council chairman Mark Epstein said in the statement. “Amtrak owes it to LIRR riders to comprehensively inspect all Amtrak facilities used by the LIRR and confirm that no critical safety issues are present.”

Moorman said Amtrak and the FRA have launched a joint inspection of the infrastructure in and around Penn, through which 650,000 people travel each day, and that he is personally leading a “comprehensive review” of all of Amtrak’s maintenance practices that could include independent consultants.

Moorman described the condition of Amtrak’s infrastructure as “fair” and added that the federally funded railroad has been challenged by budget cuts in recent years.

Metropolitan Transportation Authority Board member Mitchell Pally, who has pushed for the MTA take over control of Penn, said, with a national intercity rail network to maintain, Amtrak cannot properly prioritize the station. But, he said, it is a top priority for the MTA, which runs more trains there than both Amtrak and NJ Transit and could run even more under a plan to link Metro-North to the Western Manhattan hub by 2023.

“Obviously, Amtrak has not kept up the amount of maintenance that is necessary, otherwise all of these things would not be happening at the same time,” said Pally, who expressed relief that the latest service disruptions would be over soon. “You do kind of hold your breath as to what’s coming next.”