CONGRESS TOOK a courageous and historic step last week toward making the criminal justice system more fair.

House lawmakers embraced a measure to reduce the 100-to-1 sentencing disparities between crack and powder cocaine; the Senate approved the proposal in the spring. The president is expected to sign the bill on Tuesday.

For the past three decades, those arrested for crack offenses -- mostly young, African American men -- faced far harsher penalties than the white and Hispanic suspects most often caught with powder cocaine. A person found holding 500 grams of powder cocaine would face a five-year mandatory minimum; crack offenders would have to be in possession of a mere 5 grams to face the same obligatory sentence. Crack offenders faced a 10-year mandatory minimum for carrying 10 grams of the drug; the same penalty would not kick in for a powder-cocaine suspect unless caught with 1,000 grams.

The Fair Sentencing Act of 2010 reduced the disparity to 18 to 1. An offender would have to be convicted of peddling 28 grams or more of crack to be hit with a five-year mandatory sentence. A 10-year prison term would be handed down for 280 grams or more. (Penalties for powder offenses are unchanged.) The legislation also eliminates a mandatory minimum sentence for simple possession -- a significant advance in and of itself.

Some critics of the crack sentences have pushed for complete elimination of the disparities. But this ignores some data that crack has a slightly more powerful and immediate addictive effect and more quickly devastates the user physically than does powder cocaine. It also fails to acknowledge the higher levels of violent crime associated with crack. The 18:1 compromise fairly reflects this reality.

Assistant Senate Majority Leader Richard Durbin (D-Ill.) and Sen. Jeff Sessions (R-Ala.) deserve credit for hammering out the compromise and shepherding the bill through the Senate; House Majority Whip James E. Clyburn (D-S.C.) and Bobby Scott (D-Va.) were instrumental in advancing the bill in the House. Much credit also belongs to Families Against Mandatory Minimums, which for years pushed relentlessly for a fair corrective to the abusive sentencing laws.