CLEVELAND - The Nuclear Regulatory Commission is investigating whether the owner of the Davis-Besse nuclear plant altered records and withheld information about its damaged reactor head, The Plain Dealer reported Friday.

The NRC subpoenaed 30 boxes containing 44,000 documents from FirstEnergy Corp.'s nuclear division and has questioned plant personnel, company spokesman Todd Schneider told the newspaper.

"We are fully cooperating with that effort," he said.

The plant has been shut down since February, when inspectors discovered that boric acid had nearly eaten through the reactor head's steel cap. It was the most extensive corrosion found on a U.S. nuclear reactor and led to a nationwide review of all 69 similar plants.

A coalition of 14 environmental and nuclear watchdog groups is trying to convince the NRC of the need for an independent review of repairs and reforms at the plant 25 miles east of Toledo.

Coalition spokesman David Lochbaum, a nuclear engineer with the Union of Concerned Scientists, said an NRC source told him the agency is investigating material that FirstEnergy used in persuading the NRC to postpone a special safety inspection at the plant last fall.

The NRC suspected that Davis-Besse's reactor lid had cracks and should be immediately shut down for inspection, but ultimately accepted FirstEnergy's arguments, The Plain Dealer reported.

When workers conducted the safety check in March, they found a large rust hole all the way through the 6-inch-thick lid.

The watchdog groups claim the NRC is investigating:

_Whether date stamps on company videotapes of reactor lid inspections were altered so that older tapes - filmed when the lid was less obscured by boric acid residue - could be substituted for tapes from more recent inspections.

_Whether paperwork documenting the lid's condition was changed to reflect what the tapes supposedly showed.

_Whether the company withheld a photograph from an April 2000 inspection that showed streaks of red rust and boric acid residue on the huge dome-shaped lid.

_Whether NRC Chairman Richard Meserve lied or provided misleading information in a letter to Reps. Edward Markey, D-Mass., and Marcy Kaptur, D-Ohio. Meserve wrote the letter June 28 to explain why the agency allowed postponement of the Davis-Besse inspection.

Workers removed the damaged reactor head at Davis-Besse on Thursday and were to begin installing the replacement part.

The plant is expected to be operational by October, Schneider said.

Lochbaum, who said NRC investigators have interviewed him, said the groups he represents want the NRC to delay the plant's restart until the agency's investigations are finished.

"It's important that the NRC assure themselves that any workers currently at the plant are not suspected of any kind of wrongdoing," Lochbaum said.