WASHINGTON -- Federal judges have broad leeway to impose shorter prison terms for crack cocaine and other crimes, the Supreme Court said Monday in a pair of cases that bolster arguments for reducing differences in sentences between crack and powder cocaine.

The court, by 7-2 votes in both cases, upheld more lenient sentences imposed by judges who rejected federal sentencing guidelines as too harsh.

The decision was announced ahead of a vote scheduled for today by the U.S. Sentencing Commission, which sets the guidelines, that could cut prison time for as many as 19,500 federal inmates convicted of crack crimes.

Justice Ruth Bader Ginsburg, writing for the majority in the crack case, said a 15-year sentence given to Derrick Kimbrough was acceptable, even though federal sentencing guidelines called for Kimbrough to receive 19 to 22 years.

"In making that determination, the judge may consider the disparity between the guidelines' treatment of crack and powder cocaine offenses," Ginsburg said.

The issue has a strong racial component. Kimbrough, a veteran of the first Gulf War, is black, as are more than 80 percent of federal defendants sentenced in crack cases. By contrast, just more than a quarter of those convicted of powder cocaine crimes last year were black.

The Sentencing Commission recently changed the guidelines to reduce the disparity in prison time for the two crimes. New guidelines took effect Nov. 1 after Congress took no action to overturn the change. Today's vote is whether to apply the guidelines retroactively.

Monday's Supreme Court ruling grew out of a decision three years ago in which the justices ruled that judges need not strictly follow the sentencing guidelines. Instead, appellate courts would review sentences for reasonableness, although the court has since struggled to define what it meant by that term.

The guidelines were established by the Sentencing Commission, at Congress' direction, in the mid-1980s to help produce uniform punishments for similar crimes.

Justice Samuel Alito, who with Justice Clarence Thomas dissented in both cases, said that after Monday's decisions, "Sentencing disparities will gradually increase."

The second case decided by the court did not involve cocaine. The justices upheld a sentence of probation for Brian Gall for his role in a conspiracy to sell 10,000 pills of ecstasy.

U.S. District Judge Robert Pratt of Des Moines, Iowa, determined that Gall had voluntarily quit selling drugs several years before he was implicated, stopped drinking, graduated from college and built a successful business. The guidelines said Gall should have been sent to prison for 30 to 37 months.

"The sentence imposed by the experienced district judge in this case was reasonable," Justice John Paul Stevens said in his majority opinion.

Stevens cautioned federal appeals courts to step in only when judges abuse their discretion.

Appeals courts in both cases tossed out the lesser sentences imposed by the judges. The Bush administration urged the Supreme Court to follow suit and order tougher sentences.

Monday's rulings could embolden trial judges to vary their sentences from the guidelines more frequently and diminish the chances that appeals courts will overturn those sentences, said Douglas Berman, a sentencing expert at the Ohio State University law school.

Kimbrough's case, though, did not present the justices with the ultimate question of the fairness of the disparity in crack and powder cocaine sentences. Congress wrote the harsher treatment for crack into a law that sets a mandatory minimum five-year prison sentence for trafficking in 5 grams of crack cocaine or 100 times as much cocaine powder. The law also sets maximum terms.

Seventy percent of crack defendants are given the mandatory prison terms.

Kimbrough is among the remaining 30 percent who, under the guidelines, are supposed to receive even more time in prison because they are convicted of trafficking in more than the amount of crack that triggers the minimum sentences.

"A reviewing court could not rationally conclude that it was an abuse of discretion" to cut four years off the guidelines-recommended sentence for Kimbrough, Ginsburg said.

The court's decision and the Sentencing Commission's change in the guidelines leave untouched the minimum sentences, which only Congress can alter.

"There still is going to be a problem of what many perceive to be unjustly long sentences for low level crack offenders," Berman said.

Chief Justice John Roberts and Justices Stephen Breyer, Anthony Kennedy, Antonin Scalia, David Souter, Ginsburg and Stevens formed the majority in both cases.

The cases are Kimbrough v. U.S., 06-6330, and Gall v. U.S., 06-7949.