British justice, regarded here as incorruptible as the Crown, has been rocked by a study that accuses lawyers, judges and police of systematic infairness toward criminal defendants.

The inquiry by a pair of Birmingham University lecturers is so devastating that the nation's most prestigious lawyers tried but failed to suppress it.

The chief findings of the report, "Negotiated Justice - Pressures on Defendants to Plead Guilty" are:

Busy barristers - trial lawyers - frequently threaten their clients with heavy sentences if they insist on a trial and do not plead guilty. Some judges directly enter into this plea-bargaining process, a practice most Britons thought was unique to the United States.

A man arrested for a crime is rarely allowed to have his lawyer present when he is questioned, an issue on which British police can exercise their own discretion. A substantial number of suspects who plead guilty allege they were beaten by police.

Similar charges have frequently been made against U.S. police and court procedures, but it is widely at variance with the way most Britons understand their system.

The nation's top lawyer, Peter Webster, as chairman of the Bar last spring urged Home Secretary Merlyn Rees to suppress the report. The Home Office financed the research.

Webster complained that the findings were worthless because they depend largely on the unchecked complaints of criminals. It is not known whether Webster also told Rees that the researches wanted to question lawyers but the bar had told its members that cooperation would breach the lawyer-client relationship.

Rees said he did not like the study but had no power to stop it.

The report was also denounced by David Napley, president of the Law Society. This governs the other body of lawyers here, the solicitors who prepare a case before it reaches court where the barristers take over.

Napley said in an interview: "It's just not research if you talk to a lot of crooks about what they though and then accept whatever they tell you."

The lawyers' pressure has been so great that Birmingham University took the unusual step of submitting the study to three distinguished professors before it was released. They concluded that the work was "academically respectable" and demonstrates "there is a problem needing further investigation."

The Birmingham lecturers, John Baldwin, 32, and Michael McConville, 33, focussed on plea bargaining, inducing a defendant to plead guilty on the promise of a lighter sentence. They looked at Birmingham Crown Court, the criminal trial court, over a 15-month period and discovered that 150 defendants had abandoned their "not guilty" plea just as their trial was to begin. The pair tracked down and interviewed 121 of these at length.

They found only 35, fewer than one in three, who said the plea change was entirely their own idea. Most of these were plea bargaining work for them. The remacning 86 were either offered a deal or persuaded by "pressure from [their] barrister," fendants are to be believed, the judges themselves entered into the bargaining. One defendant said his lawyer saw the judge, came back and reported:

"Well, the judge says we can argue as long as you like but you'll be found guilty anyway."

In other cases, the defendants said that the judge's role had been indicated indirectly. According to one account:

"The barrister said, 'I'll do a deal for you. You won't get more than two and a half years. The judge knows what's going on, but we can't tell you . . . Otherwise you'll get four years.'"

Many of those interviewed by Baldwin and McConville said that their barrister, a figure at the top of the well-paid legal profession here, had not bothered to master the details of their case and was too busy to listen to them. Until the day of trial, a defendant here is likely to see only his solicitor.

To get some measure of whether defendants are wrongly pressured to plead, the Birmingham researchers called on a retired court officer and a retired police official. This part examined all the documents in each case and concluded that 21 per cent had stood a good chance of winning acquittal. The prosecution of seven was characterized as "not justified." In other words, it appears that at least seven innocent men had been pressed to plead guilty from fear of suffering a greater sentence.

Many barristers warned against attempting to complain in court about mistreatment by police. "All this mud that yoy want to sling at the prosecution and the police, it's all going to come back to you," one lawyer reportedly threatened his client.

If the Birmingham defendants can believed, they had much to complain of. Only six of the 121 were allowed to have a solicitor present during questioning in the police station. The police here can bar an arrested man's lawyer if they think it will hamper their inquiry.

Some 49 of 121 claimed that the police had attributed statements to them they had not made, "verbals" in the court jargon here and admissible as evidence.

More than one-fifth, 25, alleged they had been beaten in the station house.

Baldwin and McConville conclude that "the police station is sometimes a law unto itself" and called for "imperative" reform.

Plea bargaining, they noted is justified in the name of relieving clogged courts, but it is "unconscionable" to reduce a sentence in return for a plea andbreeds "serious miscarriages of justice Q." They want it stopped.

Several wrongly convicted persons have been freed from jail here recently so there is public suspicion of criminal justice. nade from a young cousin.