WASHINGTON – The Obama administration on Wednesday signaled a sharp departure from 20 years of federal policy and called on Congress to close the huge disparity in prison sentences for those dealing crack versus powdered cocaine, agreeing with critics who say it is unfair to blacks.

Assistant Attorney General Lanny Breuer said the administration believes the so-called mandatory minimum sentencing guidelines are so unfair that they have undermined trust in the country’s judicial institutions, particularly among minorities who bear the brunt of the law.

Breuer and other witnesses testifying before a Senate Judiciary subcommittee said the policies, launched when authorities feared crack was becoming an epidemic in the mid-1980s, are based on faulty assumptions that have long since been discredited, including that crack users were far more violent and dangerous to the community than were powdered cocaine users.

But the Justice Department and Congress under three administrations, Democrat and Republican, have supported the sentencing guidelines. Currently, it takes 100 times more powdered cocaine than crack cocaine to trigger the same harsh mandatory minimum sentence.

Breuer said the administration and its Justice Department now support equal sentences, and that additional prison time should be reserved for people who use weapons in drug trafficking crimes.

“This administration believes our criminal laws should be tough, smart, fair, and perceived as such by the American public,” Breuer said in testimony before a Senate Judiciary subcommittee, at which there was testimony about the devastating effects of the crack policy.

Breuer said Attorney General Eric Holder has established a task force that will review the issue to determine how to proceed fairly, especially on the potentially explosive issue of establishing a policy that is retroactive.

Opponents of the current policy such as Families Against Mandatory Minimums said the policy shift could affect thousands of families torn apart by the sentencing guidelines, but only if Congress passes legislation to transform it into law.

“This means a great deal, and more than symbolically. But it is Congress that has to actually pass legislation to address this,” said Mary Price, FAMM vice president and general counsel.

She noted that several bills are pending on the House side but that previous efforts by some senators to address the disparity were unsuccessful and that none are pending currently in the Senate.

Breuer and other witnesses noted that applying a new law retroactively could swamp the courts with many thousands of crack dealers currently in prison who want their sentences reduced.

The U.S. Sentencing Commission took an incremental step toward such retroactivity several years ago, which has strained the courts, U.S. District Judge Reggie Walton testified, representing the Judicial Conference of the United States.

“Has it placed a burden on the courts? Yes, it has,” said Walton, a former federal prosecutor and drug policy official appointed by President George W. Bush, and an outspoken opponent of the current policy. “But I don’t think we can let that burden impair us from doing what fundamentally has to be done to make our process fair.”

Several senators, most of them Democrats, indicated that they want to support such a change in policy, even applying it retroactively. But they said they want to hear more details first about how it could be implemented.

In the past, conservative senators have opposed changes in the law, saying they did not want to go easy on crack dealers. But little of that was in evidence Wednesday.

Sen. Lindsey Graham, R-S.C., said he was concerned about testimony that some juries were voting not to find people guilty rather than saddle them with long prison sentences for crack.