Anatoly Grishchenko, a Soviet helicopter pilot who contracted leukemia after what was hailed as a heroic effort to try to douse the fire at the Chernobyl nuclear plant, has died at age 53. Grishchenko had been in critical condition with a lung infection for more than two weeks at Fred Hutchinson Cancer Research Center, where he had received a bone-marrow transplant April 27 in an attempt to conquer his leukemia. He died late Monday of cardiopulmonary failure, said spokeswoman Susan Edmonds. Grishchenko in 1986 repeatedly flew his heavy-lift copter through the intensely radioactive gases spewing from the Chernobyl plant, dumping sand and cement in an overmatched effort to cap the crippled reactor. He and a handful of others in the operation were designated heroes of the Soviet Union, that country's highest honor. Despite lead shielding on the aircraft and other protective gear, Grishchenko suffered radiation sickness and was found to have radiation-related leukemia last year. He arrived in Seattle on April 11 for the marrow transplant, which was performed after chemotherapy and radiation treatment to kill off his own marrow. The transplant went smoothly, but Grischenko's condition suddenly deteriorated in mid-June. Antibiotics had failed to knock out the lung infection, which Grishchenko developed before coming to Seattle. The pre-transplant therapy leaves patients with no natural immunity against disease until the new marrow, which is transplanted intravenously, takes hold. ``There's a lot of sadness. It's been difficult watching him not progress, and as with all our patients, we hope they come here, be treated and go home and have a long life,'' Edmonds said. ``It was very sad to watch him have problems and grow worse.'' Grishchenko's wife of 27 years, Galina, was at his bedside, Edmonds said. At least 31 deaths are officially blamed on the April 26, 1986, explosion and fire at the plant in the Ukraine. Scientists say many more people may eventually be stricken with radiation-related diseases.