WASHINGTON (AP) — The Justice Department said Tuesday that a proposal that would result in shorter prison sentences for drug criminals should apply to some, but not all, drug felons who are currently behind bars.

A proposal adopted in April by the U.S. Sentencing Commission, which establishes sentencing policies, would lower the sentencing levels used by judges in sentencing drug traffickers. The commission estimated at the time that about 70 percent of federal drug trafficking defendants would qualify for reduced sentences and that the change, if implemented, would help cut the federal prison population by more than 6,500 inmates over the next five years.

Proponents, including Attorney General Eric Holder, have said the reduced guideline levels — which would apply across different drug types — would trim costs from a bloated and overcrowded prison system and ensure that low-level, nonviolent drug dealers are not punished too harshly.

On Tuesday, Holder called for the Sentencing Commission proposal to be applied retroactively to cover nonviolent drug prisoners who have limited criminal pasts and who did not use a weapon during their crime. As many as 20,000 prisoners, or about one-fifth of the current federal drug offender population, would be eligible to apply for reduced sentences under the criteria backed by Holder, the Justice Department said.

"Not everyone in prison for a drug-related offense would be eligible," Holder said in a written statement. "Nor would everyone who is eligible be guaranteed a reduced sentence. But this proposal strikes the best balance between protecting public safety and addressing the overcrowding of our prison system that has been exacerbated by unnecessarily long sentences."

The proposal is part of a broader rethinking of criminal justice policy within the Obama administration. The Justice Department in April, for instance, revamped its clemency process to encourage more nonviolent federal prisoners to apply for shorter sentences and said it was expecting thousands of additional petitions for leniency. And in August, Holder directed prosecutors to stop charging many nonviolent drug defendants with offenses that carry mandatory minimum sentences.

The Sentencing Commission received testimony Tuesday on whether the change should be applied retroactively, but a vote was not expected until next month.

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