Two new reports, issued Monday by the Sentencing Project in Washington and by Human Rights Watch in New York, both say the racial disparities reflect, in large part, an overwhelming focus of law enforcement on drug use in low-income urban areas, with arrests and incarceration the main weapon.
But according to the New York Times, the murderous crack-related urban violence of the 1980s, which spawned the war on drugs, has largely subsided, reducing the rationale for a strategy that has sowed mistrust in the justice system among many blacks.
In 2006, according to federal data, drug-related arrests climbed to 1.89 million, up from 1.85 million in 2005 and 581,000 in 1980.
More than four in five of the arrests were for possession of banned substances, rather than for their sale or manufacture. Four in 10 of all drug arrests were for marijuana possession, according to the latest F.B.I. data.
Apart from crowding prisons, one result is a devastating impact on the lives of black men: they are nearly 12 times as likely to be imprisoned for drug convictions as adult white men, according to the Human Rights Watch report.
Others are arrested for possession of small quantities of drugs and later released, but with a permanent blot on their records anyway.
Both Democratic presidential candidates, Senator Barack Obama of Illinois and Senator Hillary Rodham Clinton of New York, have strongly condemned the racial disparities in arrests and incarceration during their campaigns, although neither has said how they would end them.
Some crime experts say that the disparities exist for sound reasons. Heather Mac Donald, a fellow at the Manhattan Institute in New York, said it made sense for police to focus more on fighting visible drug dealing in low-income urban areas, largely involving members of minorities, than on hidden use in suburban homes, more often by whites, because the urban street trade is more associated with violence and other crimes and impairs the quality of life.
"The disparities reflect policing decisions to use drug laws to try and reduce violence and to respond to the demand by law-abiding residents in poor neighbourhoods to clean up the drug trade," Ms. Mac Donald said.
Limited efforts have been made to shift policies in ways that may reduce racial differences. Many states are experimenting with so-called drug courts, which send users to treatment rather than prison. This does not, however, affect arrest rates, which have lifelong consequences even for those who are never convicted or imprisoned.
Police in a few cities including Denver, Seattle and Oakland, California, have said they are spending fewer resources on arrests for lower-lever offenses like marijuana possession.
In December, the United States Sentencing Commission amended the federal sentencing guidelines for convictions involving crack cocaine, which is more often used by blacks, somewhat reducing the length of sentences compared with those for convictions involving powder cocaine. But mandatory and longer sentences for crack violations remain embedded in federal and state laws.