Pentostatin and Rituximab in Treating Patients With Low-Grade Non-Hodgkin's Lymphoma or Chronic Lymphocytic Leukemia

DISEASE CHARACTERISTICS: * Histologically confirmed low-grade non-Hodgkin's lymphoma * REAL classification: * B-cell chronic lymphocytic leukemia * Prolymphocytic leukemia * Small lymphocytic lymphoma * Follicular center lymphoma (grade I, II, or III) * Extranodal marginal zone B-cell lymphoma Malt type * International Working Group classification: * Small lymphocytic/chronic lymphocytic leukemia (CLL) * CLL with lymph node involvement allowed * Small lymphocytic plasmacytoid * Follicular small cleaved cell * Follicular mixed small and large cell * Follicular predominantly large cell * Measurable disease * Lymph node more than 1 cm in longest transverse diameter NOTE: A new classification scheme for adult non-Hodgkin's lymphoma has been adopted by PDQ. The terminology of "indolent" or "aggressive" lymphoma will replace the former terminology of "low", "intermediate", or "high" grade lymphoma. However, this protocol uses the former terminology. PATIENT CHARACTERISTICS: Age: * 18 and over Performance status: * ECOG 0-2 Life expectancy: * More than 6 months Hematopoietic: * Absolute neutrophil count at least 1,000/mm\^3 * Platelet count at least 75,000/mm\^3 * Hemoglobin at least 9 g/dL Hepatic: * Bilirubin no greater than 2.0 mg/dL * AST no greater than 5 times upper limit of normal Renal: * Creatinine less than 2.0 mg/dL * BUN normal * Urinalysis normal Cardiovascular: * LVEF normal in patients with history of stable heart disease for at least 2 years Other: * HIV negative * No thyroid disease with thyroid function that cannot be maintained in the normal range * No other prior malignancy unless progression free for more than 5 years * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy: * Prior rituximab, Y2B8, or iodine I 131 tositumomab allowed provided at least 6 months have elapsed and patient has had clear disease progression * No other concurrent immunotherapy Chemotherapy: * No more than 6 prior chemotherapy drugs * No more than 3 prior treatments with pentostatin * At least 3 weeks since prior chemotherapy * No prior cumulative lifetime dose of more than 480 mg/m2 of doxorubicin or an equivalent dose of any anthracycline * No other concurrent chemotherapy Endocrine therapy: * Not specified Radiotherapy: * No concurrent radiotherapy to an indicator lesion Surgery: * Not specified Other: * No other concurrent investigational drug