WASHINGTON -- Attorney General Eric Holder sought support Wednesday for erasing the gap in prison sentences for crack and powder cocaine crimes, a disparity that hits black defendants the hardest.

The effort to change federal sentencing laws for cocaine has broad support but may still unravel amid disagreements about how equal the sentences should be, and whether the whole sentencing system needs to be changed.

"One thing is very clear: We must review our federal cocaine sentencing policy," Holder said at a legal discussion sponsored by the Congressional Black Caucus.

Under current law, it takes 100 times more powdered cocaine than crack cocaine to trigger the same harsh, mandatory minimum sentences.

"This administration firmly believes that the disparity in crack and powdered cocaine sentences is unwarranted," Holder said. "It must be eliminated."

The law was passed in the 1980s during the spread of crack in American cities, which officials blamed for a rise in violence. Yet in the years since, worries about crack have declined.

The most recent government figures show that 82 percent of crack offenders are African-American, while just 9 percent of them are white.

In remarks at the Congressional Black Caucus event, Supreme Court Justice Stephen Breyer, who helped craft the sentencing guidelines that now are the subject of so much criticism and debate, urged Congress to focus first on the laws creating mandatory minimums for certain crimes.

"My goodness, those mandatory minimums drive (sentencing) guidelines in 100 different ways," Breyer said.

The justice acknowledged that curtailing mandatory minimums is not politically popular, or easy. "It's very, very hard to explain to people," he said.

The Obama administration wants to change the law to end the 100-to-1 ratio in sentencing, and make it strictly 1-to-1. Some lawmakers also want to change the law but aren't sure it should be reduced that drastically. There also is debate over whether to close the gap by raising the penalty for powder cocaine, in addition to lowering the penalty for crack.

Holder, the nation's top law enforcement officer and a former judge in Washington, D.C., said that juries have acquitted black defendants because they knew the suspects faced what jurors viewed as an unfairly long prison sentence.

The 100-to-1 ratio "is racial discrimination in practice," said Rep. Bobby Scott, D-Va., who is pushing legislation that would end the gap by eliminating crack as a category in the criminal code.

"I think there is a complete consensus that the present pattern for sentencing crack and powder is absurd," Scott said. "There is not complete consensus about what to do about it."

Mark Osler, a law professor at Baylor University and a former prosecutor, said there is general agreement on changing the law on crack cocaine but that any such change is likely to lead to other, more difficult questions.

"Going to 1-to-1 is a big change. The question that really hasn't been resolved is 1-to-1 at what level. Is the penalty for cocaine powder going up?" Osler asked. "Also, there's a general consensus that we'll see something happen with crack. I'll be very interested to see if they argue for a move toward broader reform in sentencing."

The Bush administration fought vigorously to preserve the current drug law that President Obama, Democrats and some Republicans say is unfair and outdated. Individual prosecutors and judges have also criticized the law.