RATIONALE: Drugs used in chemotherapy, such as cytarabine and daunorubicin, work in different ways to stop the growth of cancer cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as gemtuzumab ozogamicin, can block cancer growth in different ways. Some block the ability of cancer cells to grow and spread. Others find cancer cells and help kill them or carry cancer-killing substances to them. It is not yet known whether cytarabine and daunorubicin followed by gemtuzumab ozogamicin is more effective than cytarabine and daunorubicin in treating acute myeloid leukemia or myelodysplastic syndromes.