WASHINGTON. — Before the City of New Orleans and other passenger trains got the disappearing railroad blues, the Illinois Central was, for hundreds of thousands of rural blacks, a steel highway to the promised land. They left from small depots in the Deep South and arrived at Chicago's cavernous 12th Street Station. There they turned a few miles south toward what became the largest concentration of black Americans.
Now comes ''The Promised Land,'' Nicholas Lemann's riveting report on the Mississippi-to-Chicago component of the northward migration of 6.5 million blacks, one of the world's largest and swiftest migrations.
Mr. Lemann's book resembles Jacob Riis' ''How the Other Half Lives,'' written in 1890 about immigrants from Europe. Riis wrongly said they ''carry their slums with them wherever they go.'' Sharecroppers carried the culture of poverty to cities, but not forever.
Whereas the 19th-century immigrants' experience convinced Americans that slum life was a temporary fate for one generation, today the intergenerational transmission of poverty in ghettos suggests that the principal cause of continuing poverty is the enveloping set of urban poverty conditions.
To say poverty is self-perpetuating is not to blame the victims by saying that it is produced by irremediable flaws that are finally the fault of the poor. But it is to define the challenge, which is to acculturate the underclass to the disciplines and rigors of urban working life.
The underclass, writes Mr. Lemann, ''lacks a human face -- its most publicized members are criminals, and otherwise it is a mass of frightening statistics.'' He has found faces to illustrate our history, faces like that of Ruby Lee Haynes.
She was born in Mississippi in 1916 to an unwed 15-year-old. Mr. Lemann tells her story from Mississippi to Chicago and back to Mississippi where, when Mr. Lemann takes leave of her, she is living next door to an unwed 15-year-old mother of two.
Most American blacks are middle-class. However, a disproportionate share of the 20 percent of American children who live in poverty are black. Many are in female-headed households in urban settings where ways of life transplanted from the vanished world of sharecropping have been intensified by urban density and hazards.
Mechanical cotton-pickers destroyed the sharecropper system that had replaced slavery and had itself been virtual slavery buttressed by real terror. It was peonage: In 1965, Martin Luther King met Alabama sharecroppers who, having been paid all their lives in plantation scrip, had never seen U.S. currency. In the sharecropper society of enveloping despair, there often was no money for weddings, and no formal divorces because there were no possessions to divide. All the weaknesses of the urban underclass were present -- illegitimate child-bearing, female-headed households, violent crime, substance abuse (mostly home-brew whiskey, but drugs, too).
The arrival in America's cities of millions of internal immigrants, a sizable minority of whom were singularly unprepared to prosper there, reached a crescendo just as the political will and economic means to cope with the challenge collapsed, and many of the jobs that had drawn them north dried up. In the 1960s, Watts and Vietnam shattered the liberal consensus. Bewilderment replaced confidence among policy makers because of a startling ''disaggregation'': welfare cases rose as unemployment fell.
Since the oil shocks of the 1970s and the deficits of the 1980s and now the 1990s, the nation has felt unable to undertake new social programs. Furthermore, Americans do not see the urban underclass as composed of people like Rosa Parks of Montgomery or the children of Birmingham or the marchers of Selma -- decent people handicapped by clear obstacles that will yield to crisp government actions.
Mr. Lemann, having immersed himself in the chaos of real lives, has standing to say that we now know what will not work in the way of ameliorative policies, and that we have not adequately tried what might work. The cure for poverty is neither income redistribution nor the acquisition by the poor of political power. There is no longer a link between political empowerment and individual economic advancement.
In ghettos, ''self-help'' means moving out, away from high crime and bad schools. So for those left behind, a ''services strategy'' rather than an ''income strategy'' may be best after all. For a fraction of the cost of the savings-and-loan bailout, or a small fraction of the annual debt-service component of the federal budget, more police could be put on foot on the meanest streets, schools where the tax base is worst could be improved, Head Start and other forms of early intervention in the most vulnerable lives could be expanded.
The richness of Mr. Lemann's reporting, which rises to the level of literature, demolishes both fashionable despair about government policies and the facile optimism that economic growth will cure the ghettos. A rising tide does not raise all boats.
Mr. Lemann's unforgettable book -- this reader has never learned so much about contemporary America from a single book -- demonstrates that those stuck in the mud have unique problems and a uniquely powerful claim on our help.
George F. Will is a syndicated columnist.