DISEASE CHARACTERISTICS: Primary or therapy-related myelodysplastic syndrome: Refractory anemia with excess blasts Refractory anemia with excess blasts in transformation Chronic myelomonocytic leukemia Refractory anemia, refractory anemia with ringed sideroblasts, or refractory cytopenia with multilineage dysplasia These patients must also have one of the following criteria: Greater than 4 units of RBCs transfused within the past 3 months OR Platelet count less than 50,000/mm3 OR Neutrophil count less than 1,000/mm3 AND a recent infection requiring antibiotics

PATIENT CHARACTERISTICS: Age: Over 15 Performance status: 0-2 Life expectancy: Not specified Hematopoietic: See Disease Characteristics Hepatic: Bilirubin no greater than 1.5 mg/dL SGOT no greater than 2 times upper limit of normal Renal: Creatinine no greater than 1.5 mg/dL Other: Not pregnant or nursing Fertile patients must use effective contraception Free of any evidence of prior cancer for at least 12 months

PRIOR CONCURRENT THERAPY: Biologic therapy: At least 1 month since prior interferon No prior hematopoietic growth factors or cytokines except epoetin alfa No concurrent epoetin alfa Chemotherapy: No prior topotecan No prior chemotherapy for this disease At least 12 months since prior chemotherapy for another disease No other concurrent chemotherapy Endocrine therapy: At least 1 month since prior corticosteroids No concurrent hormonal therapy for disease-related conditions Concurrent steroids for adrenal failure allowed No concurrent dexamethasone and other steroidal antiemetics Radiotherapy: No prior radiotherapy for this disease At least 12 months since prior radiotherapy for another disease Surgery: Not specified Other: No prior cytotoxic therapy (including low-dose antimetabolites) for this disease At least 1 month since prior retinoids