The chief of operations at the Drug Enforcement Administration on Wednesday called the legalization of marijuana at the state level “reckless and irresponsible,” warning that the movement to decriminalize the sale of pot in the United States will have severe consequences.

“It scares us,” James L. Capra said, responding to a question from a senator during a hearing focused on drug cultivation in Afghanistan. “Every part of the world where this has been tried, it has failed time and time again.”

Capra’s comments marked the DEA’s most public and pointed criticism of the movement toward decriminalization in several states, where local officials see it as an opportunity to generate tax revenue and boost tourism.

The Justice Department decided last summer it would not challenge state laws passed in Colorado and Washington after voters supported proposals to decriminalize the sale of marijuana for recreational use. The sale and use of marijuana remains unlawful under federal law, but the Obama administration has indicated that it will not prosecute ordinary recreational users in states where consumption is legal.

Sales began in Colorado this month and will soon start in Washington. Officials in several other states are contemplating similar changes to their laws.

Capra said agents have watched the early days of legal marijuana sales in Colorado with dismay.

“There are more dispensaries in Denver than there are Starbucks,” he said. “The idea somehow people in our country have that this is somehow good for us as a nation is wrong. It’s a bad thing.”

Capra said that senior DEA officials have faced uncomfortable questions from law enforcement partners abroad. During a recent global summit on counter-narcotics in Moscow, he said, he and the head of the DEA were at a loss to explain the loosening drug laws.

“Almost everyone looked at us and said: Why are you doing this [while] pointing a finger to us as a source state?” he said. “I don’t have an answer for them.”

Officials in the District are among those contemplating changes to local codes that could lead to the legalization of marijuana. The D.C. Council’s public safety committee on Wednesday approved a proposal that makes possession of a small quantity of marijuana a minor offense, punishable with a citation similar to a parking ticket.

Support for legalization among District residents has increased markedly in recent years. A new Washington Post poll shows that nearly 63 percent of residents support decriminalizing pot. Four years ago, residents were evenly split on the issue.

Capra said he worries about the long-term consequences of the national mood on marijuana, which law enforcement experts call a gateway to more dangerous drugs.

“This is a bad experiment,” he said. “It’s going to cost us in terms of social costs.”