TOLEDO – An engineer and a contractor accused of hiding information about the most extensive corrosion ever found at a U.S. nuclear reactor first misled regulators and then lied to them, a federal prosecutor said yesterday.

Attorneys for both men denied the charges, saying the two never were in a position to know how bad an acid leak had become at the Davis-Besse nuclear plant near Toledo.

Rodney Cook, a private contractor, and David Geisen, the plant’s former engineering design manager, are the first to go to trial over the damage found at the plant in 2002.

The acid leak nearly ate through the reactor vessel’s 6-inch-thick steel cap. It’s not clear how close the plant was to an accident.

Following the discovery, the U.S. Nuclear Regulatory Commission beefed up inspections and training and began requiring detailed records of its discussions with plant operators.

The plant’s operator, Akron-based FirstEnergy Corp., paid a record $28 million in fines a year ago while avoiding federal charges.

It also spent $600 million making repairs and buying replacement power while the plant was closed from early 2002 until 2004.

None of the company’s senior leaders were charged in the investigation.

Cook and Geisen and a third former Davis-Besse employee were accused of misleading regulators in the fall of 2001 into believing the plant was safe so that the company could delay a shutdown for a safety inspection.

Shutting down the plant earlier would have been costly to the company.

Federal prosecutor Tom Ballantine said Geisen and Cook told regulators that the area of the plant the NRC was concerned about had been inspected and that there was no reason to worry.

But the inspections weren’t fully completed and the pair knew it, Ballantine said. And letters that included damaging information were previously revised.