Phase I portion (patients in strata 1A, 1B, and 2) (phase I closed to accrual effective 10/27/2003): Patients receive oral gefitinib once daily. Treatment repeats every 4 weeks for 13 courses (1 year). Patients also receive standard brain irradiation once daily, 5 days a week, for 6 weeks beginning concurrently with initiation of the first course of gefitinib. Treatment continues in the absence of disease progression or unacceptable toxicity.