WISCASSET, Maine (AP) _ Fire severely damaged the non-nuclear part of the Maine Yankee nuclear power plant, officials said Tuesday. They said the reactor shut down normally, no radiation was released and nobody was injured.

U.S. Rep. Thomas Andrews accused Maine Yankee officials of withholding details about the fire's severity when it began Monday night. Plant officials denied trying to downplay it.

''The public has a right to know exactly what occurred,'' said Andrews, a Maine Democrat. ''They should be given all the details surrounding the accident and the ensuing investigation as quickly as possible.''

On Monday night, Maine Yankee officials confirmed a fire had broken out, but gave no indication of its severity and said they could provide no details until Tuesday. Late Tuesday morning, the Nuclear Regulatory Commission revealed the first description of the fire and details of the damage.

Company officials believe the fire probably began with a fault, or short- circuit, in the transformer or sparks in the generator, said Maine Yankee President Charles Frizzle. That could have ignited hydrogen, which is used as a coolant for the generator.

The company said Tuesday that the plant's main generator may have sustained ''serious damage'' during the fire, but that it could be several days before the extent was known.

Frizzle called the fire ''probably the most serious event'' at the plant in its 19 years. He stressed no one was injured and the blaze posed no danger to the public.

The fire began 6:32 p.m. Monday and was classified as an ''unusual event,'' the lowest of four ratings the NRC gives to nuclear plant incidents.

NRC spokeswoman Diane Screnci said that authorities on the scene reported ''a loud boom'' preceded the hydrogen fire, but she said investigators were unsure whether an explosion occurred.

The NRC's initial report of the incident said ''reports were received of an explosion in the main transformer and of multiple hydrogen fires in the turbine hall.''

Charles Marschall, the NRC's senior resident inspector at the plant, said the fire was fueled by hydrogen and damaged the plant's main transformer, electrical conductors and wires leading from the generator to the transformer.

The transformer feeds electricity produced by the plant to the transmission system outside the plant, the company said.

At a news conference Tuesday afternoon, Frizzle said the fire could have happened at any power plant - nuclear or non-nuclear, such as a coal- or oil- fired plant.

''I don't want to downgrade the seriousness of the event, but it's not a nuclear event,'' he said. ''From my perspective, this should not reflect negatively on the use of nuclear power. It has nothing to do with nuclear power.''

If the generator is not damaged, the plant will be shut down for several weeks while officials replace the transformer. If the generator is inoperable, the plant may be down for several months while a new generator is installed, Frizzle said.

Officials were investigating the source of the fire, which occurred 100 to 200 feet from the containment building that encases the plant's nuclear reactor within a 4 1/2 -foot wall of concrete reinforced with steel.

The plant was operating normally when the main transformer failed, and the reactor shut down automatically, officials said. The fire was fueled by leaks in hydrogen lines running under the generator, officials said. Hydrogen ''is a very common means of cooling large generators,'' said plant spokesman Duggan Kimball.

Plant firefighters initially pumped carbon dioxide into the building to try to extinguish the blaze, but later elected to let the hydrogen fire burn itself out, which it did at 10:03 p.m., officials said.

The NRC's Screnci said no radiation was released during the incident, adding: ''On the non-nuclear side, the damage was severe because of the (apparent) explosion. The primary side, the nuclear side, responded as it should have and things went well.''

About 38 percent of Maine Yankee's 840 megawatts of electricity goes to Central Maine Power Co., the state's largest utility. The rest is sold to other utilities in Maine and other New England states. Central Maine Power spokesman Mark Ishkanian said the Maine Yankee shutdown won't cause any immediate problems.

Several residents of Wiscasset, a town of about 6,000 people about 40 miles north of Portland along the coast, were alarmed by the fire.

''I'm concerned about that place,'' said Mildred Curtis, a waitress at a diner near the plant. ''I never wanted it. ... It's really getting too old now. The place is getting worn out.''

Some anti-nuclear groups contended Maine Yankee attempted to hide the fire's severity from the public.

''We saw the same thing at Three Mile Island, we saw the same thing at Chernobyl,'' said Scott Denman, director of the Safe Energy Communication Council, a Washington-based environmental group.

But company officials denied trying to whitewash the incident or play down its seriousness.

''We haven't deceived anybody. We stand by everything we've said as being accurate,'' Maine Yankee spokesman Duggan Kimball said.