Updated

Attorney General Alberto Gonzales (search) called Tuesday for requiring federal judges to adhere to guidelines that set mandatory minimum prison sentences, saying there is evidence of growing disparity in jail terms since a landmark Supreme Court ruling.

Gonzales, speaking to a conference of the National Center for Victims of Crime (search), also said judges should retain their discretion in imposing harsher prison terms than set out in sentencing guidelines.

Sentencing guidelines (search) for federal prisoners have been in place for nearly two decades. But the Supreme Court in January said making the guidelines mandatory violated a defendant's Sixth Amendment (search) right to a jury trial because they call for judges to make factual decisions that could add to prison time, such as the amount of drugs involved in a crime.

Under the ruling, the guidelines now are only advisory. As a result, federal judges are free to sentence convicted criminals as they see fit, but they may be subject to reversal if appeals courts find them "unreasonable."

Gonzales said that since the court ruling, he has seen "a drift toward lesser sentences," while prosecutors have reported that defendants are less willing to cooperate without the threat of certain prison terms.

In one case in South Carolina, a man pleaded guilty to federal weapons and drug-trafficking charges and would have faced up to 27 years in prison under the guidelines, Gonzales said.

"The judge sentenced him to only 10, offering no explanation," he said, adding that the government is appealing the sentence.

Of 14,572 sentences imposed between the Jan. 12 ruling and May 5, there were 1,659 — or 11.4 percent — that did not comply with the guidelines, according to statistics compiled by the U.S. Sentencing Commission. Of those cases, 201 sentences were heavier than those suggested by the guidelines and the rest were lighter.

Legislation in Congress would set mandatory minimums for many types of crime, because of concern over leniency.

Former Attorney General Edwin Meese, a Republican, and former Deputy Attorney General Philip Heymann, a Democrat, are among those urging Congress not to rush to make changes, saying the system is not in crisis.