A veteran federal judge criticized tough mandatory sentencing guidelines Thursday as he imposed life sentences on four reputed gang members in their 20s for distributing crack cocaine on the South Side.

The judge also sentenced two others to 30 years in prison each and gave the girlfriend of the ringleader, a 20-year-old mother, a 10-year term.

While making it clear the defendants warranted "significant punishment," U.S. District Judge Marvin Aspen lamented that the guidelines tied his hands and didn't let him mete out punishment based on the convicts' varying roles in the crime.

Defense lawyers said the guidelines also unfairly penalize dealers of crack cocaine more than distributors of powdered cocaine, imposing prison terms 100 times greater for possessing the same amount of narcotics.

Standish Willis, one of the defense lawyers, said that since about 90 percent of crack is sold in African-American neighborhoods, the much stiffer penalties are racially motivated and unconstitutional.

Some of the defendants were also bitter that their cocaine suppliers, two middle-aged men, had received substantially reduced prison sentences because they pleaded guilty and testified against the others at trial.

The guidelines, in effect for almost seven years, are often criticized by judges at sentencing. The judges believe the guidelines take away their discretion.

Aspen, who is expected to become the chief federal judge in Chicago next year, said the guidelines won public support with the promise that they would end disparity in sentencing, punishing criminals proportionately.

"I think we can see with this case how farcical that notion is," he said.

Under the guidelines, Aspen had no choice but to impose life sentences on the ring's leader Dontay Banks, 25; his top lieutenant, Robert Shipp, 21; and Mario Dunlop and Alton Mills, both 25, because of the amount of crack distributed.

Since the judge determined that the ring distributed some 20 kilograms of crack, the guidelines required sentences of 30 years to life. Other factors, including whether the defendants had leadership roles in the distribution, made life imprisonment the only alternative.

By comparison, a defendant convicted of distributing powdered cocaine must be shown to have sold a minimum of 1,500 kilos to qualify for the same sentence of 30 years to life, defense lawyers said.

Aspen imposed minimum, though still stiff, sentences: 30 years in prison for Michael Wills, 21, and Robert Gaines, 20, and a 10-year prison term for Banks' girlfriend, Monica Boguille.

A federal jury convicted the seven defendants of narcotics conspiracy last December.

The two suppliers, Carneil Simmons, 48, and L.C. Godfrey, 54, testified at trial that they delivered more than 85 kilos of cocaine to Banks from fall 1991 to May 1993, according to Assistant U.S. Atty. Morris Pasqual.

Simmons was previously sentenced to 11 1/2 years in prison and Godfrey to a 9-year term.