RATIONALE: Drugs used in chemotherapy use different ways to stop tumor cells from dividing so they stop growing or die. Radiation therapy uses high-energy x-rays to damage tumor cells. Combining radiation therapy with chemotherapy may kill more tumor cells.

PURPOSE: Phase II trial to study the effectiveness of procarbazine, lomustine, and vincristine followed by radiation therapy in treating adults who have supratentorial glioma.

OBJECTIVES: I. Estimate the response rate of patients with newly diagnosed supratentorial low-grade glioma following neoadjuvant chemotherapy with PCV (procarbazine/lomustine/vincristine). II. Describe the toxicity of PCV. III. Determine the incidence of disease progression in these patients during PCV treatment.

OUTLINE: The following acronyms are used: CCNU Lomustine, NSC-79037 PCB Procarbazine, NSC-77213 PCV PCB/CCNU/VCR VCR Vincristine, NSC-67574 3-Drug Combination Chemotherapy Followed by Radiotherapy. PCV; followed by external-beam cranial irradiation using at least 6 MV photons.

DISEASE CHARACTERISTICS: Histologically confirmed supratentorial * grade I/II glioma, including: Diffuse fibrillary astrocytoma No pilocytic astrocytoma No mixed tumor with ependymoma elements * Supratentorial sites include: Frontal, temporal, parietal, or occipital lobes Thalamus, basal ganglia, or midbrain Lateral or third ventricles Pons, medulla, or optic chiasm tumors allowed only if secondary to eligible tumor More than 1 separate tumor allowed Diagnosis based on surgical biopsy or subtotal resection Measurable or evaluable disease on T2-weighted MRI required

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0-2 Hematopoietic: WBC greater than 3,500/mm3 Platelet count greater than 130,000/mm3 Hemoglobin greater than 9 g/dL Hepatic: Bilirubin less than 2 times upper limit of normal (ULN) AST less than 2 times ULN Alkaline phosphatase less than 2 times ULN Renal: Creatinine less than 1.5 times ULN Other: No active or uncontrolled infection No second malignancy within 3 years except: Nonmelanomatous skin cancer In situ cervical cancer No pregnant or nursing women Negative pregnancy test required within 7 days prior to entry Effective contraception required of fertile patients

PRIOR CONCURRENT THERAPY: Biologic therapy: Not specified Chemotherapy: No prior chemotherapy Endocrine therapy: At least 1 week since prior steroids OR Stable steroid dose for at least 1 week prior to study Radiotherapy: No prior cranial or head and neck irradiation Surgery: See Disease Characteristics