Leahy has invited Attorney General Eric Holder and Deputy Attorney General James Cole to testify at a September 10 hearing about Washington and Colorado legalizing small amounts of marijuana for personal use, as well 20 states and Washington D.C. legalizing medicinal marijuana.

Nearly a year after voters in two states legalized marijuana possession, the Senate Judiciary Committee chairman once again plans to ask Justice Department officials how they will handle the conflict between state and federal marijuana laws.

When it comes to marijuana laws, Senator Patrick Leahy (D-Vt.) wants to know whether the U.S. Department of Justice plans to prosecute or pass.

But Holder and the Department of Justice have given no public indication of the federal government's planned response to the state initiatives. Holder, testifying in the Senate in March, said he would reveal a policy "relatively soon." In the meantime, Colorado officials told TPM last week that they believe the delay amounts to "tacit approval" from the Justice Department to implement the marijuana laws.

Yet the U.S. Drug Enforcement Agency continues to list marijuana in the same schedule as the most dangerous controlled substances. The Justice Department has not made any response to the state statutes, leaving uncertainty about whether, for instance, a Coloradon carrying a joint would face federal prosecution.

Leahy has written the director of the Office of National Drug Control Policy about the issue, and questioned whether state officials who license marijuana retailers are risking prosecution for carrying out their duties.

"It is important, especially at a time of budget constraints, to determine whether it is the best use of federal resources to prosecute the personal or medicinal use of marijuana in states that have made such consumption legal," Leahy said in a written statement. "I believe that these state laws should be respected. At a minimum, there should be guidance about enforcement from the federal government."

Holder drew criticism from some medical marijuana advocates for a speech earlier this month concerning mandatory-minimum sentences, which are often in play in drug cases. Holder, in his remarks, did not get into the tension between state and federal marijuana laws.

The chairman of a group opposed to the criminalization of marijuana, Marijuana Majority, said Holder's high-profile speech gave reformers hope the Justice Department would back off enforcement of marijuana laws in Colorado and Washington.

"We're still waiting for the administration to announce its response to the marijuana legalization laws in Colorado and Washington, a policy that the attorney general has been saying is coming ‘relatively soon’ since December," Tom Angell, the group’s chairman, said in a statement.

"If the administration is serious about using law enforcement resources in a smarter way, it should be a no-brainer to strongly direct federal prosecutors to respect the majority of voters by allowing these groundbreaking state laws to be implemented without interference."