Attorney General Alberto R. Gonzales yesterday called for a new system of mandatory minimum sentencing rules, contending that recent Supreme Court decisions have already led to "a drift toward lesser sentences" in federal criminal cases.

In his first major remarks on the topic since being named attorney general, Gonzales said that high court rulings in January have produced uneven sentences in the federal court system and deprived prosecutors of "a critical law enforcement tool."

The former Texas Supreme Court judge suggested that the Justice Department would favor a plan to mandate minimum sentences while allowing judges to impose longer terms at their own discretion.

"Our sentencing system works best when judges have some discretion, but discretion that is bounded by mandatory sentencing guidelines created through the legislative process," Gonzales said in a speech to a gathering here of the National Center for Victims of Crime.

Gonzales's comments provide the clearest indication yet of the Bush administration's preferred strategy for dealing with a pair of Supreme Court rulings that have roiled the federal courts and put a halt to two decades of increasingly tough sentencing rules.

In the rulings, separate Supreme Court majorities found that the way the guidelines were administered violated a defendant's right to a jury trial because judges were allowed to impose sentences based on allegations that were not considered by the jury. The court also ruled that the guidelines should be advisory, not mandatory.

Gonzales argued in his speech yesterday that prosecutors have already seen evidence that sentences are trending down, and he pointed to several cases. In South Carolina, Gonzales said, a violent felon who pleaded guilty to weapons and drug charges would have faced 27 years in prison under the old guidelines -- but was given 10 years instead without explanation from the judge.

"We risk a return to the pre-guidelines era, when defendants were encouraged to play the odds in our criminal justice system, betting that the luck of the draw . . . might result in a lighter sentence," Gonzales said.

He cited statistics from the U.S. Sentencing Commission that found that adherence to the guidelines was 70 percent in 2003, compared with 63 percent in the four months after the Supreme Court rulings this January.

But other figures muddy the picture. Commission statistics also show that sentences were within the guidelines 65 percent of the time in fiscal 2002 and 64 percent in 2001, closer to the more recent rate. Figures are not available for fiscal 2004.

While not explicitly endorsing any particular proposal, Gonzales said that one idea "deserving of serious consideration" would be guidelines that established mandatory minimum sentences and advisory maximum sentences. Such a system, he argued, "would be fully consistent with the Sixth Amendment as interpreted by the Supreme Court."

Last month, House Republicans passed an anti-gangs bill that would, among other things, subject gang members to lengthy mandatory minimum prison sentences. The measure's prospects are uncertain in the Senate, however, and Democrats have urged caution in responding to the Supreme Court's sentencing decisions.

Douglas A. Berman, a law professor at Ohio State University and a sentencing expert, said the Justice Department is seeking to take advantage of "a loophole of sorts" in the patchwork of recent court rulings. Some critics have dubbed the idea "the topless guidelines system," he said.

"This is the 'Have your cake and eat it, too' approach that the Justice Department would like to have," Berman said. "Judges would not be limited in how harsh they can be, only in how lenient they can be."

Attorney General Alberto R. Gonzales said federal prosecutors see evidence of sentences trending down in the absence of guidelines for judges.