Even as the first residents trickle into city-sanctioned dispensaries for medical marijuana, the District is locking up more people than ever for marijuana possession, according to an ACLU analysis released Tuesday.

Possession arrests surged more than 60 percent between 2001 and 2010, one of the largest increases in the nation, the civil liberties group found. Arrests of African Americans accounted for much of that increase, raising concerns among community leaders and criminal justice experts about racial profiling by police.

“I travel around the city and I see undercover ‘jump-out’ cars east of the river, and I don’t see them uptown or in Georgetown,” said the Rev. Anthony J. Motley, a prominent Southeast pastor. “We want the laws enforced, but make it equal.”

Based on 10 years of census and FBI crime data, the study found that on average, an African American is nearly eight times as likely to be arrested for marijuana possession as a white person, even though blacks and whites use marijuana at similar rates.

The report — “The War on Marijuana in Black and White” — says such racial disparities in possession arrests were found in all regions of the country. “In over 96 percent of counties with more than 30,000 people in which at least 2 percent of the residents are black, blacks are arrested at higher rates than whites for marijuana possession,” it says.

Of those arrested for possession in the District, nine out of 10 were African American, a statistic matched only by Baltimore. By contrast, 82 percent of those arrested in Philadelphia were black, and in Brooklyn, 62.5 percent were black.

Between 2001 and 2010, the disparity in possession arrests between blacks and whites widened, the analysis found — particularly in the District, said Ezekiel Edwards, director of the ACLU’s criminal law reform project and an author of the report.

Peter Reuter, a public-policy professor at the University of Maryland who has studied arrest rates for marijuana possession, said age also plays a factor. “If you are a marijuana user under the age of 21, you have a much higher chance of getting arrested than a 35-year-old,” he said.

Reuter has found the same widening of racial disparities in arrests for marijuana possession in his own research. The reasons behind the increase in possession arrests among African Americans, however, is unclear, he said.

“The real puzzle is why is this going on. If you look at statements by police chiefs across the country, you don’t see a crackdown on marijuana. It seems to be the result of other kinds of arrest strategies,” Reuter said.

One possible example is the New York police department’s controversial “stop-and-frisk” policy, in which officers who have a “reasonable” suspicion that someone has or will commit a crime and is a threat may stop that person and frisk for weapons.

The policy has been criticized as a form of racial profiling, but Reuter noted that there have been increases in marijuana possession arrests in parts of the country where there is no stop-and-frisk.

In the Washington area, Reuter found that the majority of those arrested for possession are rarely sentenced to prison. He added that marijuana possession arrests appeared to increase in the District after 2009, further suggesting that a change in police tactics may have resulted in more arrests.

In a statement, D.C. Police Chief Cathy L. Lanier said her office needs to take a closer look at the report, but she denied that the city has made a concerted effort to target marijuana possession.

“Since day one, my priority has been combating violent crime, and the District is safer as a result,” she said.

Lanier also agreed with the ACLU’s conclusion that the number of arrests is not a good measure of police performance. She asked: “Isn’t it better for a community if arrests drop because there are fewer crimes?”

A D.C. police source also noted that the ACLU report’s aggregated data don’t account for the fact that in 2012 and 2013, the percentage of blacks arrested was 85 percent, far lower than the 91 percent for 2010.

The ACLU cast its findings as further support for decriminalizing marijuana, which the report calls “the smartest and surest way to end targeted enforcement of marijuana laws in communities of color.”

Legalization has been steadily gaining traction in recent years. The District and 17 states have legalized medical marijuana, and national polls have shown a shift in public opinion, with a majority of Americans in support of some form of legalization.

“The country seems to be saying it’s time to treat marijuana as a public-health issue like alcohol, and yet we are spending millions on arrests for possession in communities of color,” Edwards said. “It’s a peculiar crossroads we are at.”