ALLAN PINKERTON The First Private Eye By James Mackay John Wiley. 256 pp. $27.95 THIS BIOGRAPHY of Allan Pinkerton should have been a terrific book. The founder of the world's most famous detective agency, now boasting 250 offices in 20 countries, Pinkerton was born in a Glasgow slum in 1819. He died nearly 65 years later in a downtown Chicago mansion, known as the inventor of the "private eye" trademark with the slogan "We Never Sleep." The young barrel-maker who had begun his career as a militant "physical force" Chartist (suffrage reformer) in his twenties had by the 1850s become Chicago's best-known detective, an associate of Abraham Lincoln and intimate of George B. McClellan (then a railroad executive, later a top Union general). Pinkerton, who had learned a hatred of slavery from Chartism, made his home a station on the Underground Railway; in the spring of 1859, he raised $600 for the notorious John Brown, who was on his way from Kansas to Canada with a group of runaway slaves. When rumors surfaced of a plot to assassinate the President-elect in Baltimore as he traveled to Washington for his inauguration in early 1861, Pinkerton devised the subterfuge by which a disguised Lincoln slipped into the capital secretly at 6 a.m. -- accompanied by the detective and his operatives. Pinkerton's friendship with McClellan paid off in a Civil War assignment to create a Secret Service for the Department of the Ohio. This intelligence operation, using spies who could move on both sides of the lines, followed McClellan up the military ladder. When the general took over the Army of the Potomac, he brought Pinkerton with him to Washington, where he managed a spy network while investigating fraud and Confederate espionage in the city. Pinkerton's Washington star faded when Little Mac was sacked for excessive caution by Lincoln in late 1862; his best operative, the double agent Timothy Webster (who was eventually executed), had inadvertently contributed to McClellan's downfall by overestimating Confederate strength around Richmond. After the war, Pinkerton's business grew West along with the railroads and the new express companies' needs for protection. Although agents solved a number of high-profile bank robberies, they also came in for bad publicity, as members of the Reno gang (captured by Pinkertons) were hanged by vigilantes; and Jesse James's gang not only eluded Pinkerton operatives (killing two) but also gained public sympathy when a detective tossed a bomb into the James homestead, killing Jesse's 8-year-old half-brother. Allan Pinkerton is best remembered by historians, however, for his role in infiltrating a secret, violent Irish miners' organization, the Molly Maguires, in the anthracite fields of northeastern Pennsylvania. Hired by Reading Railroad President Franklin Gowan, Pinkerton placed his most famous informant, James McParlan, in the Mollies for over two years; his testimony eventually helped send 20 men to the gallows in 1877. Thereafter, even though Pinkerton's security business became his major revenue source, the agency became infamous for providing labor spies and company goons. Allan Pinkerton had been dead six years in July, 1892, when 300 armed Pinkertons sailed up the Ohio River in an unsuccessful attempt to dislodge 10,000 armed, striking steelworkers at Carnegie's Homestead Works. The ensuing gun battle, in which dozens were shot (and 16 killed) on both sides and the Pinkertons were routed, made the Pinkerton name synonymous with the union-busting efforts of the late 19th-century robber-barons. As a private police force, the agency, which could call on 30,000 reserves, outnumbered the active-duty strength of the U.S. Army. Pinkerton's key agent surfaced again in 1907 in the trial of Big Bill Haywood and two other principals in the Western Federation of Miners for the murder of the anti-labor former Idaho governor Frank Steunenberg -- the incident at the heart of the late Anthony Lukas's recent book, Big Trouble. James McParland (having added a "d" to his name) induced suspect Harry Orchard to produce a lurid 135-page "confession" implicating the union and its leaders in numerous murders. This time the defense had Clarence Darrow; McParland's techniques came under withering, eloquent scrutiny, and the three were acquitted. This is great material for a fascinating biography. To his credit, Mackay tells a good yarn, and his accounts of Pinkerton's early cases, the Lincolns' secret detour, and McParlan and the Mollies are good reading. But he also makes errors that are instructive for biographers. Though acknowledging that Pinkerton was a bully as a husband, boss and father, he can brook no criticism of his subject's public life. Mackay's intense partisanship leads him into tenuous defenses of McClellan's generalship, for example, and of a Pinkerton operative's incitement of lethal vigilante violence against suspected Mollies. Writing about one of the most intensely studied periods in American history, he refers in his notes and bibliography to just three sources published in the last 25 years. Mackay avoids the effort, central to the biographer's task, of connecting the apparently disparate cords of Pinkerton's political views -- militant Chartism, support for runaway slaves, insurrectionary abolitionism -- to his career protecting businesses first from theft (for which, by the way, he hired women detectives), later against union organizing, and to his family life. Warren Goldstein teaches American history at the University of Hartford. He is writing a biography of William Sloane Coffin Jr. CAPTION: Allan Pinkerton