GLEN RIDGE— WHEN Eldon and Betty Allin decided to move into a four-bedroom Colonial on Carteret Street in 1961, her father warned against it. ''Don't buy it,'' he told them. ''It's built on a dump.'' He knew because he worked at Public Service Electric and Gas, and had installed all the original gas meters on the block. The Allins bought the house anyway.

They didn't discover how right he was until 22 years later. Then one evening, on vacation in Florida, they saw their street on television. The Federal Environmental Protection Agency had just announced that an extensive area of radium contamination had been found in Essex County. The Allins, and their neighbors, were living atop radium waste discarded more than half a century earlier from a nearby watch-dial factory. The dirt in their yard was radioactive, with a half-life of 1,600 years.

The discovery changed their lives. In time, they would be moved out of their house until their lawn could be torn up, excavated and replaced. They would have to collect and send in regular air samples from their basement. They would get used to the men in anti-contamination gear, the hazardous material warnings, the regular letters from E.P.A. And they would learn more than anybody really wants to know about Superfund, the Federal program for cleaning up toxic waste disasters.

They never moved from Carteret Street, nor were they ever quite convinced that the soil posed any real danger. ''I asked: Prove to me, show me the records, show me that people have become ill from this,'' Mr. Allin said.

But recently Mrs. Allin has been collecting names of people in the neighborhood who have died of lung cancer, the main health risk linked to such contamination. So far she has found four, but she wonders about neighbors who moved away. She has developed lymphoma herself, and she wonders if there is a connection. (A 1988 epidemiological survey by the state did find increased lung cancer rates in the area but noted that the sample size was small.)

And there are small things about living on a Superfund site that you never get used to. All day long, huge trucks filled with 20 tons of radioactive dirt from Carteret Park rumble by, rattling Mrs. Allin's china and making cracks in her walls. ''There's constantly dirt,'' she said. ''Worse than the digging is the backwards beep.''

When the story of Love Canal broke in the late 1970's, Americans discovered a dark side of having the world's most successful industrial economy. Congress responded to the proliferation of abandoned toxic dumps by passing the Superfund law in 1980; it requires those responsible for toxic wastes to clean them up and, where the polluter can't be found or made to pay, cleans up those sites using fees collected from certain heavy industries. ''Superfund is a program that is dealing with the sins of the past,'' said John Frisco of the E.P.A., who has been responsible for the agency's toxic cleanup effort in New Jersey for the past seven years.

As far as past sins go, few states have more to atone for than New Jersey. There are 116 Superfund sites here, more than any other state. ''Industry started here,'' Mr. Frisco explained. ''Wastes were handled improperly by today's standards.'' Industrial horrors in New Jersey include thorium contamination from the manufacture of gas lamps in Maywood, an asbestos dump in Millington and mercury contamination from the manufacture of vapor lamps in Hoboken.

A Superfund site is seldom hard to recognize: go to a place where hazardous materials were carelessly produced or stored or dumped, and there you are. But in Glen Ridge, you could spend all day walking around the 90-acre site -- this utterly typical neighborhood of 1930's houses on shady streets, of flower gardens and jungle gyms and dogs -- and never guess the source of the contamination.

Half a mile away, in Orange, is the abandoned factory where the U.S. Radium Corporation made luminous watch dials from 1915 to 1926. At the time, nobody knew radium was dangerous; it was only after women who worked at the factory began getting sick and dying of cancer that the Essex County medical examiner, Dr. Harrison A. Martland, spotted the connection.

By that time, soil tainted with radioactive tailings from the factory had been used to fill in low-lying areas of Essex County -- a total of 210 acres in Glen Ridge, Montclair and West Orange. It was not until 1981 that the E.P.A. -- as part of a national initiative -- conducted an aerial survey of the 12 square miles around the U.S. Radium plant. Ground surveys over the next two years confirmed the presence of dangerous gamma radiation, and the problem was first revealed publicly at the end of 1983.

A byproduct of decaying radium is radon, a gas that is not dangerous in the open but can lead to lung cancer if it is concentrated inside a house. When the problem was first detected, radon levels in some houses were 100 times the safe level. Within days of announcing the problem, the E.P.A. began installing lead shields and ventilation systems in the most contaminated homes.