Drugs used in chemotherapy work 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. Flavopiridol may make the tumor cells more sensitive to radiation therapy. Phase I trial to study the effectiveness of combining flavopiridol with radiation therapy followed by gemcitabine hydrochloride in treating patients who have locally advanced, unresectable pancreatic cancer.