HOSPITALIZED. JACQUELINE KENNEDY ONASSIS, 64, book editor; following surgery for a bleeding ulcer; in New York City. The former First Lady revealed in February that she was suffering from non-Hodgkin's lymphoma, at which point a family spokeswoman said doctors believed they had arrested the cancer. The stomach ailment was discovered during routine tests, and she was admitted to New York Hospital-Cornell Medical Center last week. Otherwise, said a Kennedy family spokeswoman, her cancer treatment was nearly complete.