ATLANTA (Reuters) - Black Americans are 10 times more likely to be imprisoned for illegal drug offenses than whites, even though both groups use and sell drugs at the same rate, according to a study released on Tuesday.

Almost all large counties in the United States showed sharp disparities along racial lines in the sentencing of drug offenders, the study by the Washington-based Justice Policy Institute showed.

There were 1.5 million drug arrests out of 19.5 million drug users in 2002, it said. About 175,000 people were incarcerated for a drug offense, of which half were black, even though blacks account for 13 percent of the U.S. population, it said.

The study looked at data from 198 U.S. counties with the biggest population. Its findings were similar to others on the subject, but it is the first to look at relative incarceration rates at a local level.

“What you keep seeing is this towering drug admission rate for African Americans and a very small rate for whites. In many cases, the admission rate for whites is smaller than the (percentage of whites in the) whole population,” said Jason Ziedenberg, the institute’s executive director.

The reasons for the disparity include federal mandatory minimum jail terms for drug crimes, which he said hit blacks harder.

For instance, the mandatory federal sentence is the same for possession of 5 grams (0.2 ounces) of crack, more associated with blacks, as 500 grams (18 ounces) of cocaine, which is more often used by whites.

Local police also tend to devote more resources to policing illegal drugs in open-air drug markets in inner cities with more blacks than in suburban communities or college campuses, Ziedenberg said, citing other research.

Research also shows that probation officers are sometimes more lenient with white offenders, blaming their problems on factors such as a broken home, than with black offenders, who were more likely to be described as having a failure of moral character, he said.

Ziedenberg advocated more investment in drug treatment and applauded individual U.S. counties that decided to make drug enforcement a lower priority than policing violent crime.

Reform of drug laws and increases in funding for drug treatment are difficult to achieve because politicians are unwilling to be seen as soft on crime, according to Ethan Nadelmann, executive director of the Drug Policy Alliance.

“The public is by and large supportive of (some drug) reform, but legislatures have been hesitant to move forward. ... The law enforcement industry is politically very powerful and has a lot of sway over legislators,” Nadelmann said.