Dose Escalation Study of Revlimid With Fludarabine-Rituximab for CLL/SLL

* Participants will be treated in groups (cohorts) of three to six subjects per cohort. The dose of lenalidomide or fludarabine will be increased from one cohort to the next. Regardless of the treatment cohort, participants will receive treatment in cycles lasting 28 days. * For the first 3-5 days (depending on the group), participants will be treated on an outpatient basis in the infusion room at the Dana-Farber Clinic, with fludarabine and rituximab. Fludarabine is given intravenously for 3-5 days. Rituximab is given intravenously on day 1 of each 28-day cycle. Lenalidomide is given orally once per day for 3 weeks, followed by 1 week of rest. * Participants will be monitored very closely during the study treatment. During the first 28 day period (cycle 1), a physical exam and routine blood tests will be performed weekly. All participants in a group must finish the first 28-day treatment period before we proceed with the next group. Once started on study treatment, participants will continue for six cycles (a cycle is 28 days) of combination therapy with all three drugs. During that period they will have a physical exam and routine blood tests on day 1 of each treatment cycle, and additional blood tests on day 15 of each cycle. * When participants complete 6 cycles of combination therapy, they will proceed with two additional months of the lenalidomide alone, for 21 out of 28 days. * Disease response will be evaluated after 2, 6, and 8 months of study treatment. The following tests and procedures will be performed: Physical exam; blood tests; CT scans to evaluate lymph nodes; skin testing; and bone marrow biopsy if all other tests show no evidence of any remaining CLL and if the baseline bone marrow biopsy was positive * Participants will have a physical exam and lab work every 3 months as long as their disease remains in remission.