PATERSON, N.J. (AP) _ A 12-year-old boy has been sentenced to a maximum of three years' probation after pleading guilty to setting an industrial park fire that caused $400 million in damage in Passaic and killed a firefighter.

Superior Court Judge Carmen A. Ferrante on Wednesday also ordered the youngster, whose name was withheld because of his age, to serve one year in a reformatory, but suspended the sentence.

''There are clearly extenuating circumstances in this case,'' said Ferrante, referring to the outdoor storage of hazardous materials in the industrial park. ''People knew children went in there looking for toys.''

The boy pleaded guilty Feb. 3 to setting the Labor Day blaze by throwing lit matches into pans of naphthalene.

The fire destroyed more than 30 residential and industrial buildings and left 2,220 people jobless and 400 others homeless. The fire smoldered for 40 days. An elderly firefighter suffered a fatal heart attack.

Under the terms of the probation, the youngster must attend school, maintain good grades, abide by an 8 p.m. curfew, perform community service and get counseling. He also must pay $35 to the state's Violent Crimes Compensation Board.

Another 12-year-old boy was initially charged after the defendant accused him of setting the fire.

The charges against him where dismissed when he denied in a lie detector test that he lit the naphthalene, supplied the matches or asked his playmate to light a match, said Senior Assistant Prosecutor Michael O'Shea.

Authorities said 45,000 pounds of the petroleum derivative, used to make mothballs and bathroom deodorizers, had been left in 35 stacked vats in an alley between two factories. It was cooling in the air from liquid to solid form.

The complex was fenced in, but the gate had been left open, and entry could also have been gained through holes in the fence, said O'Shea.

He said neighborhood children would often rummage through garbage bins in search of chalk, crayons, small blackboards and other items commonly discarded by the factories.

When ignited by the boy, the naphthalene burst into a torch-like flame that quickly spread to other vats and to adjacent buildings, many of which were old and had wooden window frames and oil-soaked timber floors, said the prosecutor.

The types of businesses in the complex - silk screening, fabric and wallpaper companies - helped the fire to spread, he added.

A grand jury is investigating conditions at the park at the time of the fire, Ferrante said.