Fludarabine in Treating Patients With Chronic Lymphocytic Leukemia

DISEASE CHARACTERISTICS: * Confirmed diagnosis of B-cell chronic lymphocytic leukemia (CLL) * Previously untreated * Rai stage I, II, III, or IV * Requiring systemic therapy * Persistent lymphocytosis of greater than 5,000/mm\^3 * Morphologically mature lymphocytes * Monoclonal B-cell population * CD19/CD5/CD23 positive with kappa or lambda light chain restriction by immunophenotyping * No other lymphoproliferative disorders including prolymphocytic leukemia, mantle cell lymphoma, progression to aggressive B-cell lymphoma, or Richter's syndrome * No clinical autoimmune hematologic complication of CLL including Coomb's-positive hemolytic anemia or immune thrombocytopenia * Positive Coomb's test allowed if no clinical hemolysis PATIENT CHARACTERISTICS: Age * 16 and over Performance status * ECOG 0-2 Life expectancy * At least 6 months Hematopoietic * See Disease Characteristics Hepatic * Bilirubin no greater than 2 times upper limit of normal (ULN) * AST and/or ALT no greater than 2 times ULN Renal * Creatinine no greater than 2 times ULN Other * Accessible for treatment and follow-up * No known HIV infection * No active bacterial, viral, or fungal infection requiring systemic antibiotics * No conditions requiring corticosteroid therapy * No history of other malignancies except for the following: * Adequately treated nonmelanoma skin cancer * Curatively treated carcinoma in situ of the cervix * Other solid tumors curatively treated with no evidence of disease within the past 5 years * No other major medical illness that would preclude study * No known hypersensitivity to fludarabine or its components * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception during and for at least 6 months after study PRIOR CONCURRENT THERAPY: Biologic therapy * No concurrent immunotherapy including monoclonal antibody therapy * No concurrent autologous or allogeneic stem cell or bone marrow transplantation Chemotherapy * No other concurrent cytotoxic drugs Endocrine therapy * No concurrent corticosteroids except inhaled or topical corticosteroids * No concurrent corticosteroids for nausea prophylaxis Radiotherapy * No prior radiotherapy affecting more than 25% of bone marrow and/or involving the pelvic area * No concurrent radiotherapy Surgery * Not specified Other * At least 4 weeks since prior investigational agents * No other concurrent investigational agents