Thomas Flanagan, a professor who turned a flash of inspiration into a prize-winning historical novel of Ireland, then followed it with two more acclaimed books in the same vein, died on March 21 at his home in Berkeley, Calif. He was 78.
The cause was a heart attack, said his daughter, Caitlin Flanagan.
Mr. Flanagan taught literature at the University of California at Berkeley in the mid-1970's when he had the epiphany that led to his first novel, ''The Year of the French'' (Holt, Rinehart & Winston, 1979). As he often told the story, he was in his office staring at a pad of paper, waiting for his wife, Jean, to pick him up because he did not drive.
''He just suddenly had a vision of a person walking down a road, and that is when he became a novelist,'' said Barbara Dupee, a friend whose husband, F. W. Dupee, had taught with Mr. Flanagan at Columbia University in the 1950's. The fellow on the road was a poet named Owen Ruagh MacCarthy, and the image turned into the opening chapter of ''The Year of the French,'' a sprawling tale of Ireland's doomed uprising against the British in 1798.
''I haven't so enjoyed a historical novel since 'The Charterhouse of Parma' and 'War and Peace,' '' John Leonard wrote in his review in The New York Times.
The book was no glossy version of Ireland spun from the comfort of an American campus. It was a stark and sometimes brutal account of the uprising, which began when British landlords, lured by higher profits, converted farms to grazing and evicted the tenants.
''The Year of the French'' won the National Critics Circle award for fiction. Mr. Flanagan followed it in 1988 with ''The Tenants of Time'' (Dutton), which begins in 1867. The third book in the loose trilogy was ''The End of the Hunt'' (1994, Dutton), which brought the tale into the early 20th century. In a review in The Times, Terence Brown called that book ''a significant contribution to the historical interpretation of the period.''
Thomas Flanagan was born on Nov. 5, 1923, in Greenwich, Conn. His father was a dentist, his mother a homemaker; all four of his grandparents had come to the United States from County Fermanagh.
He dominated the high school newspaper in Greenwich along with his friend Truman Capote. He interrupted his education at Amherst to serve with the Pacific Fleet, returned to complete his undergraduate work there, then went on to receive a master's degree and Ph.D. at Columbia. In 1949 he married Jean Parker, a nurse, who died last year. He is survived by Caitlin, of Los Angeles; another daughter, Ellen Klavan of Santa Barbara, Calif.; and four grandchildren.
Mr. Flanagan made a start toward his literary career early, writing stories for Ellery Queen's Mystery Magazine. At the same time he settled into a teaching post in Columbia's English department while doing his doctoral work, encountering heady intellectual times there -- Lionel Trilling was an adviser -- and publishing a scholarly work, ''The Irish Novelists, 1800-1850,'' in 1959.
In 1960 he moved to Berkeley, and into heady times of a different sort on that tumultuous campus. About this time he and his wife also began making annual trips to Ireland, Mr. Flanagan striking up friendships with writers like Seamus Heaney.
In 1978 Mr. Flanagan switched campuses again, to the State University of New York at Stonybrook. He retired in 1996 and returned to Berkeley. In retirement he continued to write essays and criticism for publications that included The Times and The New York Review of Books, which is preparing to publish a collection of his essays in book form.
Mr. Flanagan once described his affection for Ireland this way: ''It is not the romantic, rather sentimental Ireland of many Irish-Americans that I love, but the actual Ireland, a complex, profound, historical society, woven of many strands, some bright and some dark.''
Photo: Thomas Flanagan (Jerry Bauer)