OUTLINE: Patients receive cyclophosphamide IV followed by pentostatin IV on day 1 in course 1. Beginning in course 2 and in all subsequent courses, patients receive cyclophosphamide IV on day 1, pentostatin IV on day 1, and rituximab IV on day 1 or on days 1 and 2. Treatment repeats every 3 weeks for up to 6 courses in the absence of disease progression or unacceptable toxicity.