Damage to two Chinook helicopters nearing completion at the Ridley Township assembly line of the Boeing Co. was likely not accidental, but criminal investigators with the Defense Department are reserving judgment until they complete their probe, a congressman said today.

It could take several weeks before investigators determine what caused irregularities in two of the $30 million combat helicopters being assembled as part of an Army contract, said U.S. Rep. Joe Sestak (D., Pa.), whose Delaware County district includes the facility.

But Sestak, a former Navy admiral, said initial signs are that the damage, which included cut wires and other irregularities on two new helicopters, was likely not accidental.

"There's a low probability that this was not deliberate," Sestak said. "But it can't be ruled out that it was some accident or some non-deliberate occurrence."

"It may take a couple weeks now to make a final determination of how it occurred exactly," said Sestak, who was briefed after Army investigators met this morning with Boeing officials at the plant.

Production on the company's Chinook helicopter assembly line could resume as early as tomorrow after being abruptly shut down yesterday, Sestak said.

"The Defense Contract Management Agency and the program manager of the Army were there and everyone has agreed they'll be ready to move forward tomorrow with full production," said Sestak, who sits on the House Armed Services subcommittee.

Agents with the Defense Criminal Investigative Service, which is an arm of the Office of Inspector General, were on site at the facility today, Defense Department spokesman Gary Comerford said.

DCIS notified the U.S. Attorney's Office as a matter of course, Comerford said. The company, meanwhile, notified the FBI yesterday, but the bureau was only monitoring the situation today, an FBI spokeswoman said.

A representative for the unionized workers at the plant did not immediately return a call this afternoon.

Boeing spokesman Joseph L. LaMarca Jr. said the company hoped production would resume tomorrow. The company summoned federal investigators with the Department of Defense to its suburban Philadelphia helicopter facility yesterday after quality assurance employees detected what they considered to be irregularities with the military helicopters.

"They did inspections overnight, and so far it looks like there are no irregularities with any of the other aircraft on the line," LaMarca said. Boeing produces about three Chinooks a month and had a total of eight in various stages of production on its line yesterday.

Sestak said a spare washer was found in one of the helicopters in a system "where it shouldn't have been."

On a second Chinook, "there were damaged wires that appeared to be severed," Sestak said. "We don't know how or why."

The problems were detected during routine inspections of two nearly completed Chinook CH-47F's - a newer model that has not yet been deployed to combat zones.

Agents with the Defense Contract Management Agency swiftly made their way to the Boeing Rotorcraft Division to inspect the two helicopters in question, LaMarca said. The Army had notified the FBI as a matter of course, he said.

"It was determined that an investigation needed to be launched to make sure that this was an isolated incident," LaMarca said.

All Chinook production employees reported to work today as scheduled, though work remained shut down while the investigation continued, LaMarca said. The Boeing line at the Ridley plant is the only one producing Chinooks in the country.

LaMarca said it was too soon to know whether the problems detected with the two Chinook F-models were caused by a mechanical issue on the assembly line or sabotage.

"Some people threw that word around yesterday," LaMarca said, "but as the old saying goes, 'You don't know what you don't know.' "

The aircraft at issue are part of a long-term Boeing Army contract for 458 Chinook CH-47F models and MH-47G models through 2018. Some are being built from scratch and others are being "remanufactured" using recycled D-model Chinook parts on a new fuselage.

The contract is part of an effort to modernize the Army's Chinook fleet. The helicopter's tandem rotor and lack of a tail rotor make it ideal for combat in high-altitude regions, such as the mountains of Afghanistan and Iraq.

LaMarca said the company did not believe there was a problem with F-model helicopters already delivered to the Army, some of which have been declared combat-ready but have not yet been sent overseas.

The irregularities were detected by Boeing quality-assurance staff.

"We check these helicopters over from head to toe to make sure everything is done to specification so that we provide the safest, most reliable helicopter," LaMarca said.

LaMarca said that Boeing officials had not used the word "sabotage" in their review of the matter and that there appeared to be no workplace issues that would have even prompted such an action. He said that the company was not in labor talks with its unionized employees and that labor relations were in good shape.

"There's nothing to spur anybody to be upset or disgruntled," he said.

The "irregularities" were found during testing on the final production line, Sestak said.

"We don't know the cause," Sestak said this morning. "We need to find out why this happened and that's what the investigation will tell us today. I think it would be speculative to go beyond that."

More than 100 Boeing workers were dismissed at midday yesterday and hundreds of others arrived at work last night only to assist with inspections. All assembly work was halted.

Sestak said he did not know whether other helicopters produced at the plant would have to be recalled.

"It will depend on the assessment," Sestak said. "If it's systemic - and I don't think it will turn out to be - then they would go out to inspect other helicopters."

Contact staff writer Maria Panaritis at 215-854-2431 or at mpanaritis@phillynews.com.