CHICAGO — Chicago police beat, kicked, shocked, or otherwise tortured scores of black suspects in the 1970s and 1980s to try to extract confessions from them, prosecutors reported yesterday.

However, the prosecutors — appointed by a Cook County judge four years ago to look into torture allegations — said the cases are too old or too weak to prosecute anyone now.

Prosecutors Robert Boyle and Edward Egan said they found evidence that police abused at least half the 148 suspects whose cases were reviewed. Nearly all the suspects were black.

Among other things, the suspects claimed that police beat them, played mock Russian roulette, administered electric shocks with a cattle prod-like device and a crank-operated “black box,” and threw typewriter covers over their heads to make them gasp for air.

The investigators were not able to substantiate all of the allegations, but made it clear they believed many of the claims, including the use of the black box on at least one man, and said that in the majority of cases, suspects were beaten with fists, feet, or telephone books.

Messrs. Boyle and Egan said that in only three cases involving a total of five former officers was there enough evidence to prosecute, but the threeyear statute of limitations has run out.

“We only wish that we could indict on these three cases,”Mr.Boyle said, after a $6.1 million investigation that involved more than 33,300 documents, the issuance of 217 grand jury subpoenas, and interviews of more than 700 people.

Among those five officers was Jon Burge, a lieutenant who commanded a violent-crimes unit and the socalled midnight crew that allegedly participated in most of the alleged torture.

Neither Mr. Burge nor anyone else has ever been charged, but Mr. Burge was fired in 1991 after a police board found that a murder suspect was abused while in custody. Mr. Burge’s attorney has said that Mr. Burge never tortured anyone.

In their 300-page report, the prosecutors accused then-police Superintendent Richard Brzeczek of dereliction of duty and said he and a former top official at the Cook County State’s Attorney’s office, William Kunkle, failed to pursue an investigation into allegations of torture.

“They can blame me for whatever they want to blame me for,” Mr. Brzeczek said. “I know what I did was correct. It was not dereliction of duty.”

Mr. Kunkle, now a Cook County circuit judge, was not available for comment, his staff said.

Mayor Richard Daley was the state’s attorney during part of the period investigated, but Mr. Boyle dismissed any notion that Mr. Daley knew about the torture. Mr. Daley delegated responsibilities to other people in his office, and his only mistake was “perhaps relying on the judgment of others,” Mr. Boyle said.