More than 2,500 federal inmates became eligible for early release from prison starting in March after the U.S. Sentencing Commission voted Tuesday to retroactively reduce the penalties for using and selling crack cocaine.

Despite Justice Department warnings against releasing thousands of criminals, the commission voted unanimously to allow inmates to seek reduced sentences if they were convicted under tough drug laws passed in the 1980s. Those laws have come under criticism from civil libertarians and many judges, who say crack cocaine offenders are treated more harshly than users of powder, which has resulted in stiffer penalties for African Americans.

Tuesday's vote, which ultimately could affect some 19,500 federal prisoners serving time for crack convictions, came a day after the U.S. Supreme Court ruled that judges may deviate from the strict sentencing guidelines developed during the "war on drugs." The two decisions amount to a repudiation of federal law enforcement policies and a return of power to judges in dispensing justice to defendants in federal courts.

The reprieve would be unprecedented: No other single rule in the two-decade history of the Sentencing Commission has potentially affected so many inmates.

The numbers, which amount to 10% of all federal prisoners, dwarf even the grants of presidential clemency afforded draft resisters and conscientious objectors after the Vietnam War.

Those eligible for reduced sentences include 307 inmates sentenced in federal courts in California, said Thom Mrozek, spokesman for the U.S. attorney's office in Los Angeles. Mrozek said 124 of them were sentenced in the seven-county federal judicial district surrounding Los Angeles.

The bulk of inmates eligible for the sentencing break are concentrated in the South, mainly Virginia, Florida and South Carolina.

Earlier this year, the commission adopted more lenient rules for crack offenders sentenced after Nov. 1. Tuesday's vote gave federal inmates the benefit of the new regime.

More than 2,500 of them -- mainly those who have already served lengthy sentences -- would be eligible for release in the first year. About 17,000 others also would be eligible for sentence reductions, but even if they were granted, the inmates would still have time left to serve.

Members of the commission said the move was an important first step to correct what they said was a major injustice that Congress had failed to address.

"Our country has moved in the wrong direction with regard to the so-called war on drugs," Ruben Castillo, a federal judge in Chicago and a vice chairman of the commission, said before the vote Tuesday. "We need to refocus this war."

Michael E. Horowitz, a former Justice Department official and another member of the commission, said: "This is not a get-out-of-jail-free card by any means, but a fairness issue."

The far-greater punishment for crack users has been long debated. Under federal law, an individual convicted of dealing 5 grams of crack cocaine, even a first-time offender, is automatically sentenced to five years in prison. A similar sentence in a powder cocaine case must involve at least 500 grams. Lawmakers in the 1980s justified the disparity because crack was associated with violent crime and was considered more addictive.

The changes that the commission adopted Tuesday do not affect the prison terms of inmates given those "mandatory minimum" sentences, only those who received higher sentences under the guidelines. The net effect would drop the average sentence by about 27 months or about 17%.

The early release had been strongly opposed by law enforcement organizations.

"These offenders are among the most serious and violent offenders in the federal system," the Justice Department said in a statement.

With violent crime rising after two decades of steady decline, "releasing a potential 20,000 additional violent criminals onto the street prematurely is going to exacerbate the problem," said James Pasco, executive director of the Fraternal Order of Police, which represents thousands of police officers across the country.

The Justice Department added that the decision would also "divert valuable resources from federal courts and prosecutors for re-sentencing at a time when violent crime is rising in many vulnerable communities around the country."

The commission said it attempted to address such concerns. It delayed until March 3 the date upon which courts could begin entertaining sentence-reduction motions in individual cases. The hope is that judges, probation officers, prison officials and public defenders would devise a system to handle the influx in an orderly fashion.