Colorado’s top U.S. prosecutor urged cooperation between state and federal officials on marijuana policy during a congressional hearing Tuesday that was notable for showing the deepening divisions on the topic in Washington, D.C.

Although marijuana remains illegal federally, Colorado U.S. Attorney John Walsh said federal law enforcement officials must work with their local counterparts to achieve common goals such as keeping marijuana away from kids, even after states legalize marijuana for adult use.

“With our collective effort, and only with our collective effort, we can succeed in implementing effective marijuana regulatory efforts in practice and on the ground,” Walsh said in testimony before a subcommittee of the U.S. House’s Committee on Oversight and Government Reform.

The hearing was the subcommittee’s second under the title, “Mixed Signals: The Administration’s Stance on Marijuana.” But rather than clarifying those signals, the hearings mostly illuminated why they exist.

Much of Tuesday’s hearing consisted of lawmakers battering a top Drug Enforcement Administration official with questions about his agency’s resolute stance against marijuana — as the official, deputy administrator Thomas Harrigan, reiterated that the DEA sees “no sound scientific, economic or social reasons to change our nation’s marijuana policies.”

That clashes with what President Barack Obama said in an interview with The New Yorker magazine published earlier this year, when he said marijuana is not more dangerous than alcohol and that marijuana enforcement disproportionately punishes minorities. Of marijuana legalization in Colorado and Washington state, Obama said: “It’s important for it to go forward.”

In line with that, the Department of Justice last year issued guidance to allow state legalization of marijuana to proceed without federal interference so long as the states address eight key priorities — including preventing stoned driving, out-of-state pot smuggling and access by youths. Walsh and Harrigan both said Tuesday the guidance has not changed their approach to marijuana, which focuses on taking down large criminal organizations.

“There has been little impact on our enforcement actions,” Harrigan said.

DEA officials, though, have pushed back against the administration’s lenience toward legalization. DEA Administrator Michele Leonhart blasted the approach during a meeting with the National Sheriffs’ Association. And another top DEA official, testifying before a different committee earlier this year, called marijuana legalization “reckless and irresponsible.”

Although Walsh and Harrigan submitted joint written testimony for Tuesday’s hearing, differences emerged during the hearing. When Harrigan quoted a statistic on the number of drivers killed in fatal car crashes who test positive for marijuana, Walsh added that he was uncertain of the statistic’s validity.

“There was a palpable difference between their approaches,” said Dan Riffle, a lobbyist for the Marijuana Policy Project who sat in on the hearing. “It seems like there’s really a pretty big divide in the administration and the Department of Justice.”

Similar to a hearing last month, members of the subcommittee repeatedly questioned Harrigan about why the DEA believes marijuana should be categorized in the same restriction level as heroin.

Harrigan responded that the DEA would “not abandon science and fact in favor of public opinion.”

That frustrated several subcommittee members, with Rep. Gerry Connolly, D-Va., asking, “Would you agree that marijuana is certainly not in the same category as heroin in terms of its danger?”

When Walsh was asked whether marijuana should be reclassified, he demurred. “There is a process,” he said.

On Wednesday, a collection of anti-drug organizations and addiction-treatment groups are expected to send a letter to federal officials urging that marijuana remain in the most restrictive category of substances, known as Schedule I.

“We remain troubled with the normalization of marijuana that continues unabated,” the letter states.

John Ingold: 303-954-1068, jingold@denverpost.com or twitter.com/john_ingold