Authoritative, even-handed, meteulously researched, Lou Cannon's President Reagan will stand as one of the great accounts of an American presidency, The presidency was nothing less than the role of a lifetime for Ronald Wilson Reagan, the first actor to ascend to the highest office in the land, He appeared, on the whole, a natural for the part, turning in a performance that seemed effortless and easy, a performance that often concealed the complexities of the man and his responsibilities, No one is in a better position to explain these complexities than Lou Cannon, who has covered the phenomenon of Ronald Reagan for over a quarter century, first as a reporter for the San Jose Mercury-News, later as The Washington Post White House correspondent. In President Reagan, a masterwork that will stand as the definitive account of the most significant American presidency since FDR's, Cannon takes us behind the all-American smile of the acting pres-ident. He uncovers the subtleties of the man whose essential optimism and shrewdness reflected the divided nature of the nation itself.