The Unforgettable Season, by G.H. Fleming. New York: Penguin Books. 334 pp. $ 5.95.
G.H. Fleming is a professor of English literature, as well as a baseball aficionado and history buff. He has combined all three interests in a book that skillfully reconstructs an unusually dramatic pennant race, while capturing the flavor of turn-of-the-century America and preserving the vintage prose of early sportswriters culled from newspapers and magazines of the time. The story is told entirely by means of excerpts.The ''unforgettable season'' is that of 1908, when public interest in the presidential election was largely overshadowed by baseball. Ultimately the New York Giants and Chicago Cubs won the right to do battle in a close World Series contest whose outcome hinged upon a single controversial play.