"The absolute criminalization of personal marijuana use has contributed to our nation's soaring prison population and has disproportionately affected people of color," Sen. Patrick Leahy, D-Vt., said Tuesday in a first-ever hearing aimed at reconciling rapidly changing state marijuana laws with a federal prohibition on the drug.

"We must have a smarter approach to marijuana policy," Leahy, chairman of the Senate Judiciary Committee, said. "Marijuana use in this country is nothing new, but the way that individual states are dealing with marijuana continues to evolve."

The hearing before the Senate Judiciary Committee follows a Justice Department memo outlining how it will enforce federal marijuana prohibitions in two states, Colorado and Washington, that have legalized its use, and 20 states that allow marijuana for medical use.

The Justice Department reserves its right to challenge state laws if public health or safety problems emerge or if the states fail to enact strict regulations to control marijuana use and sale, Deputy Attorney General James Cole, author of the memo, told the Senate panel. For now, the Justice Department will not interfere with how the states are handling legalization.