The Supreme Court restored federal judges Monday to their traditional central role in criminal sentencing.

In two decisions, the court said U.S. district judges have broad discretion to impose what they think are reasonable sentences, even if federal guidelines call for different sentences.

One decision was particularly emphatic in saying judges are free to disagree with guidelines that call for much longer sentences for offenses involving crack cocaine than for crimes involving an equivalent amount of cocaine in powdered form.

Monday's decisions include an important racial dimension: A 2002 report noted that 85 percent of defendants convicted of crack offenses were black, a fact the U.S. Sentencing Commission warned was leading to a loss of confidence in the fairness of the system.

Both cases, each decided by the same 7-2 alignment, chided federal appeals courts for failing to give district judges sufficient leeway. In each case, the appeals court had overturned a sentence that was shorter than that provided by the guidelines. The two dissenters were Justices Clarence Thomas and Samuel Alito Jr.

Judges still may not impose sentences above the range written into law by Congress or state legislatures.

But the decision Monday gives judges broad discretion to impose sentences higher or lower than the federal guidelines, which are not statutes and are issued by the Sentencing Commission.

The two decisions answered questions left hanging in 2005, when the court ruled that federal sentencing guidelines could be constitutional only if advisory rather than mandatory. Appeals courts were to review sentences for "reasonableness," the court said then. But the court did not say what it meant by either advisory or reasonableness.

"The guidelines should be the starting point and the initial benchmark," Justice John Paul Stevens said in one of the decisions Monday, Gall vs. United States.

But Stevens went on to say that the guidelines are just one factor in the "individualized assessment" that a judge must make in every case.

In that case, Brian Gall, who had briefly been involved in an ecstasy distribution ring while a college student, received a sentence of three years' probation rather than 30 to 36 months in prison called for by the guidelines.

The Eighth U.S. Circuit Court of Appeals, in St. Louis, ruled that such an extraordinary variance from the guidelines range required an equivalently extraordinary justification.

That judgment was erroneous, Stevens said, in failing to give due deference to the district judge's reasoned and reasonable decision.

The defendant in the crack cocaine case, Derrick Kimbrough, received 15 years instead of 19 to 221/2 for several cocaine and gun-related offenses.

The trial judge said the higher guidelines term would be inappropriate for Kimbrough, a Marine veteran of the Persian Gulf War with an honorable discharge.

The judge also disagreed with the relative treatment of crack and powdered cocaine, a disparity that he said led to disproportionate and unjust results.

The Fourth U.S. Circuit Court of Appeals, in Richmond, Va., overturned the sentence on the grounds that it was unreasonable for a judge to depart from the guidelines "based on a disagreement with the sentencing disparity for crack and powder cocaine offenses."

The Supreme Court took the unusual step of reinstating the original lower sentences, rather than simply instructing the appeals courts to reconsider the cases under an appropriately deferential standard of review.

In her majority opinion in Kimbrough vs. United States, Justice Ruth Bader Ginsburg took account of an important policy development since the case was argued Oct. 2. On Nov. 1, amended guidelines for crack cocaine that the U.S. Sentencing Commission had long advocated took effect when Congress, which had the power to block them, let the moment pass without acting.

Ginsburg said acceptance of the amendment by Congress undermined the government's position that judges should not have discretion to depart from the guidelines themselves. The amendments put into effect a relatively modest change that will reduce sentences for crack by about one-quarter.

The Sentencing Commission was limited in what it could accomplish on its own. A 1986 federal law, enacted at the height of public concern about crack, incorporated a 100-to-1 ratio into mandatory minimum sentences - that is, the same sentence was imposed for a given amount of crack and 100 times that amount of powder.

Bipartisan bills are pending in Congress to address the disparity. Today, the Sentencing Commission will vote on whether to make the Nov. 1 amendment retroactive to the 19,500 inmates imprisoned for crack offenses.