LANSDOWNE, Pa. (AP) _ The whole family helped out when Dican Hadjy Kabakjian began moonlighting in his basement in 1924, stretching his physics professor's salary and riding the crest of a promising new cancer treatment.

Kabakjian was a great man and a brilliant scientist, said one neighbor in the middle-class suburb of towering trees, stately old houses, quiet dead-end streets and back yards big enough for great games of hide-and-go-seek.

The business in the basement of the three-story, stucco-and-frame Victorian duplex helped get the Kabakjians through the Depression.

It also did something else: it made theirs the only single residence on the government's list of the most toxic waste sites in America.

For two decades, until Kabakjian died in 1945, the family supplied doctors and hospitals with radium-tipped needles to insert near cancerous tumors.

''I'd take the raw stuff and cook it until you get these radium crystals,'' said Kabakjian's daughter, Alice Kabakjian Lewis, 74. Her sister Louise would weigh the crushed crystals and pack them into platinum needles. The physicist's sons Armen and Raymond worked during vacations. Dicranouhi Kabakjian helped her husband when she wasn't keeping his house. Daughter Lillian kept the books.

There was no fear of radiation then; far from it. Two decades after it was discovered, radium was hailed as a miracle treatment for everything from cancer to tonsilitis. It would be years before scientists learned that radium decays into radon gas that can cause cancer. The disease may not show up for 40 years.

Someone living in the house 16 hours a day for their whole life stood a one-in-three chance of cancer, said Victor Janosik, who is managing the cleanup for the U.S. Environmental Protection Agency.

Raymond Kabakjian died at 65 of abdominal cancer, in 1977. His son, Raymond Jr., died of bladder cancer in 1983, at age 37. William Dooner, who delivered radium, died in 1984 at age 71 of cancer of the head and lungs.

Dican Kabakjian didn't develop cancer. He died in 1945, at 70, of emphysema probably caused by fumes from the acid he used to process the radium ore.

The Tallant family bought the house in 1949 and lived there until moving into a bigger place in 1961. Anna Tallant died of breast cancer in 1969, at 54.

The ''hot house'' came to light in 1962 during a search for forgotten radium sites. In 1964, authorities spent $200,000 to decontaminate it. They declared success after removing furniture, dishes, rugs and clothing, and after replacing windows, walls, sinks and a concrete basement floor. That September the couple who owned it, Harry and Mary Kizirian, moved back in.

But in 1983, during a survey of sites that might be eligible for federal cleanup assistance, the EPA found radon levels in the basement 10 times higher than allowable and gamma radiation, similar to X-rays, 3 1/2 times higher.

In 1985, the house was put on the EPA's Superfund list.

Last August, white-suited workers equipped with oxygen masks, vacuums and Geiger counters arrived. They dismantled the house board by board and brick by brick. All but 1 1/2 bricks had been contaminated with radium.

The trees where neighborhood children played were uprooted; squirrels had scampered up them carrying radioactivity from the ground where Kabakjian dumped workshop waste. The yard was dug up, too, leaving a 9-foot-deep pit.

About 240 feet of sewer line running down the street is contaminated and will have to be replaced. None of the surrounding houses have been found to be contaminated, but six lots showed higher-than-normal radioactivity, pushing the cleanup cost from $7.5 million to $9.5 million.

''I don't feel a great deal of anxiety about radiation,'' said Georgianna Gretzenberg. The back door of the house she and her husband bought in 1987 is 20 to 30 yards from the chain-link fence that surrounds the empty lot and from the trailers where workers are checked for contamination. The free-standing garage they planned to turn into a studio may be lost to the cleanup.

''It's sad to see the neighborhood ripped up. For me, it's more that,'' said Mrs. Gretzenberg, who had a healthy baby boy six months ago. ''My biggest concern is they won't finish. I hope it will be done so we can go back to doing what you do in suburbia.''

Helen Click, who has lived behind the house for 23 years, said, ''We were told as long as it's not in our house, we shouldn't be concerned.''

Richard Kizirian, whose family bought the house from the Tallants, wonders if the radium can be blamed for illnesses that afflicted his family, including sores that developed on his father's legs before he died.

''That's the $64 question. Our understanding is the long-term effects of radiation have not been proven,'' said Kizirian. He has considered suing, but isn't sure who to sue, and lawyers say he's lucky the EPA paid for the cleanup.

The costs included $140,000 paid to the Kizirians and the Basehore family, who lived in the other side of the duplex. The families retain ownership of the land, which will be filled and landscaped when the work is done this summer.

Kizirian said that given its history, he doubts anyone will buy, so he and the other heirs to his parents' estate might donate it to the town.

Nancy Basehore, who is in her 70s, declined to talk at length about her experiences, but considers Kabakjian to be a great man. She hasn't decided what to do when the property can be occupied again, either.

''Once the EPA finishes they'll certify they don't have a radiation problem,'' said George Bochanski, a borough councilman and former Environmental Protection Agency spokesman. ''That's more than some of us can say.''

Penny Flaherty, who rents the house next door, grew vegetables the summer of 1987, but Kabakjian's legacy worried her. ''It was funny, I grew them and brought them in, but I had qualms about eating them and threw them out.''