Combination Chemotherapy and Rituximab in Treating Patients With Chronic Lymphocytic Leukemia or Lymphocytic Lymphoma

DISEASE CHARACTERISTICS: * Diagnosis of B-cell chronic lymphocytic leukemia (CLL) or small B-cell lymphocytic lymphoma (SLL) with the following: * Lymph node biopsy interpreted as SLL or consistent with CLL or all of the following: * Peripheral lymphocyte count greater than 5,000/mm\^3 with small to moderate peripheral lymphocytes and no more than 55% prolymphocytes * Bone marrow aspirate containing at least 30% lymphoid cells * Immunophenotypic evaluation of peripheral blood lymphocytes demonstrating monoclonality of B lymphocytes with all of the following: * CD19 or CD20 coexpressed with CD5 antigen in the absence of other pan-T- cell markers (e.g., CD2 or CD3) * Expression of CD23 on CLL cells or Dim B-cell expression of kappa or lambda light chains * Measurable disease with any of the following: * 1 or more lymph nodes at least 1.5 cm by CT scan * Splenomegaly by CT scan * Peripheral lymphocyte count greater than 5,000/mm3 with coexpression of CD5 and B-cell markers * Bone marrow aspirate with at least 30% lymphoid cells * No mantle cell lymphoma PATIENT CHARACTERISTICS: Age * 18 and over Performance status * ECOG 0-2 Life expectancy * At least 2 years Hematopoietic * See Disease Characteristics * No immune thrombocytopenia * No hemolytic anemia Hepatic * Bilirubin no greater than 3 times upper limit of normal (ULN) * SGOT no greater than 3 times ULN (unless due to hemolysis or CLL) * No hepatitis Renal * Creatinine no greater than 1.5 times ULN Cardiovascular * No cardiac dysfunction * No New York Heart Association class III or IV heart disease * No myocardial infarction within the past month Other * HIV negative * No active acute or chronic infection * No immunosuppressive diseases * No autoimmune disorder * No secondary malignancy that is projected to limit life expectancy * Not pregnant or nursing * Negative pregnancy test * Fertile patients must use effective contraception PRIOR CONCURRENT THERAPY: Biologic therapy * See Chemotherapy * No prior rituximab * At least 4 weeks since prior biologic therapy Chemotherapy * At least 4 weeks since prior chemotherapy * No prior combination chemotherapy and rituximab or other antibody therapy * No prior combination chemotherapy comprising an alkylating agent and a purine nucleoside analog (i.e., cyclophosphamide or chlorambucil in combination with fludarabine, cladribine, or pentostatin) * No prior pentostatin Endocrine therapy * At least 4 weeks since prior corticosteroids * No concurrent supra-physiologic doses of corticosteroids Radiotherapy * At least 4 weeks since prior radiotherapy Surgery * At least 4 weeks since prior major surgery Other * No concurrent immunosuppressive therapy (e.g., cyclosporine)