In a little office on the third floor of Metropolitan Police Headquarters on Indiana Avenue NW is a small window to the future — open to some, closed to many. This is where you get your D.C. “police clearance.”

If you have never been there, that’s because you have never applied for a job flipping burgers, mowing lawns or cleaning restrooms in the District. Room 3033 is the human resources department for the poor, the young and the disenfranchised. The piece of paper you get there — if you have no criminal record — is what you need to land a job. Without it, you’re out of luck.

For 29 years, I have defended clients facing marijuana charges in the District. At every initial appearance, without fail, the judge admonishes the defendant either to stay in school or to hold down a job. In the majority of cases, however, a job is not possible because most employers in this town will not hire entry-level workers who do not have a police clearance.

What crime is increasingly tripping up those looking for work? Possession of marijuana.

In 1995, police in the District arrested about 1,850 people for having pot. By 2011, the number had skyrocketed to more than 6,000. It’s still rising.

To put that into perspective, there are twice as many marijuana arrests in the District as there are students graduating from D.C. high schools each year.

And though marijuana usage rates for blacks and whites are about the same, more than 90 percent of those arrested on pot charges in the District are black. Most of them are young men. By the time their cases are over, months or sometimes years later, they have gone from the unemployed to the long-term unemployed.

For young people denied jobs, crime and public assistance become far more enticing. Marijuana laws create a permanent underclass of people unable to join the legitimate workforce.

The Eighth Amendment of the Constitution prohibits “cruel and unusual punishments.” Is it not cruel, and unusual, to deny a young person caught with a bag of weed his chance for entry into productive society? Long experience shows that legitimate employment is the best remedy for youthful indiscretions.

The costs of our current marijuana policy are extraordinary, both for those arrested and for society. We are spending millions of dollars, and tens of thousands of hours’ work by police, enforcing punitive marijuana laws. Add up what is spent on the arrests, booking, forensic testing, prosecution, court-appointed lawyers, judges, marshals and probation officers, and the cost of a single marijuana prosecution can begin to rival the cost of sending a student to college.

There are two types of marijuana users the District. Those who have avoided arrest, and those whose lives are derailed by involvement with the criminal courts. The first group is predominantly white and privileged. The second, black and disadvantaged. Research confirms what many people of color suspect: The disparity between white and black marijuana arrests is the result of racial bias in the application of the law.

I talked a great deal about this issue when I ran for D.C. Council in April’s special election. I didn’t win, but that doesn’t mean that the city’s leaders can’t take a sensible action to improve the prospects of thousands of young people.

It’s time for Mayor Vincent C. Gray (D) and the D.C. Council to decriminalize possession of small amounts of marijuana. Seventeen states and several major cities already have. Blue states such as Massachusetts and red states such as Nebraska have realized that it is counterproductive to pointlessly saddle their kids with criminal records. If Cambridge intellectuals and Nebraska “cornhuskers” can agree on decriminalizing marijuana, why can’t the District’s elected leaders figure this out, too?

Decriminalization is not legalization. With decriminalization, marijuana is still prohibited but the maximum penalty for those caught with small amounts is reduced from a criminal misdemeanor to a civil violation.

Adults are given a citation and fined. Juveniles are assigned to an educational class, and their parents are notified. Because there’s no arrest, there’s no arrest record — and no impediment to finding legitimate employment.

Public safety is not enhanced by locking up people for small amounts of pot. In fact, public safety is compromised, and society pays a hefty price, when law enforcement turns harmless young pot users into “lawbreakers” and drags them into a system that ultimately spits out them out on a dead-end street.

The writer is a D.C. lawyer.