The Government Accountability Office's indictment of the nuclear facilities and the Nuclear Regulatory Commission is the most comprehensive reckoning to date of problems that have begun to emerge at a number of plants in recent years.

Inadequate oversight and gaps in safety procedures have left several plants unsure about the whereabouts of all their spent fuel, the GAO said, and problems in tracking the materials suggest that radioactive rods could be missing from more than the three plants that are widely known to have problems.

``NRC inspectors often could not confirm that containers that were designated as containing loose fuel rods in fact contained the fuel rods,'' the report said. ``The containers, in some cases, were closed or sealed and, in other cases, the contents were not visible when looking into the spent fuel pool. Thus, spent fuel may be missing or unaccounted for at still other plants.''

The commission said it agreed with the GAO's findings of ``uneven'' control of spent nuclear fuel. NRC spokeswoman Beth Hayden said the agency had been forced to prioritize safety concerns after the Sept. 11, 2001, attacks, and that this had caused delays in implementing security measures to safeguard the spent fuel rods.

The nuclear industry pointed out that the GAO had not found evidence of adverse health consequences. Problems in accounting for the fuel are being addressed, said Steven Kerekes, a spokesman for the Nuclear Energy Institute.

Critics, however, said close ties between federal regulators and the commercial facilities they supervise has dulled the edge of oversight.

"I would respectfully remind the NRC that the `R' stands for `regulatory,' " said Sen. James Jeffords, I-Vt., who, with other members of Congress, had asked the GAO to study the issue. Rep. Bernard Sanders, I-Vt., added: ``The days of letting the nuclear industry self-regulate without proper federal oversight must come to a long overdue end.''

Three plants have reported missing or unaccounted-for spent nuclear fuel in recent years: Millstone in Connecticut, Vermont Yankee, and Humboldt Bay in California.

The report said federal regulations do not make clear how plants should conduct physical inventories of spent fuel, nor how they should control and account for loose fuel rods and fragments.

Plants had different notions about how to monitor their inventories of spent fuel, consisting of highly radioactive rods that have been removed from reactors and are generally stored in large swimming pool-like structures.

Some plants had failed to match paper records with the contents of spent fuel containers, the report said.

The GAO said the government has sufficient warning of the scope of the problem to begin implementing changes, but the NRC's Hayden said the agency is still in the process of getting the information it needs.