Walter Lewis, a Los Angeles County deputy district attorney, will not soon forget the rape case he prosecuted eight years ago.

He thought he had a strong case, but the jury was unable to reach a verdict. When he questioned the jurors later, one middle-aged woman explained that she could not vote to convict because the defendant did not confess during the trial.

"I've never seen that happen," Lewis responded, puzzled.

"You must not be very experienced," she said.

"I've been a prosecutor for 11 years," Lewis responded, growing irritated. "Why would you expect a defendant to do that?

"It happens all the time," the juror insisted.

Lewis finally realized what had happened. The juror had never been in a courtroom. She expected to hear a confession because that's what she sees in her living room, week after week, on television's fictional police and lawyer shows.

Interviews with lawyers and judges suggest that Lewis' experience was not an isolated incident. Many tell similar stories about how such shows as Perry Mason and Owen Marshall have come to influence not only jurors' expectations and decisions, but alo attorney's courtroom behavior.

"My personal opinion," said Mark Vezzani, another county deputy district attorney, "is that TV has changed the shape of the criminal justice system more than anything I know of."

Sociologists and legal experts in recent years have been studying and debating TV's impact on the courtroom. However, their focus has not been on Perry Mason and Owen Marshall, but on the news cameras that are permitted to televise trials in 23 states.

Some doubt that TV has much effect on the courts. District causal relationships are hard to prove, and one attorney cautioned that "lawyers will look for any excuse for why they lost a case."

But a number of lawyers and academics think that TV's impact is undeniable. It is simply a question, they say, of which television form -- entertainment or news programs -- is influencing the judicial system more.

Complaints about the impact of TV's fictional lawyer shows come from prosecutors and defense attorneys.

A majority of lawyers questioned said they make a point, during the preliminary questioning and selection of jurors, to warn that real trials are not like those depicted on Perry Mason. Most ask the jurors whether they will be able to put aside preconceived notions of the courtroom obtained from TV.

"Of course, the jurors always answer yes," Lewis said. "The point of our questions is just to flag the issue, to make them aware of the problem. That's all we can do."

Prosecutors say jurors with TV formed expectations assume that defendants are often falsely charged, because Perry Mason always defends innocent clients. But in the real world, 90 percent of all defendants plead guilty, often after bargaining for a reduced charge.

Prosecutors also complain that jurors exposed to TV often expect fingerprints and sophisticated scientific data to be introduced as evidence in cases where they are either not available or not needed. They point to a 1975 Rand Corp. report, "The Criminal Investigation Process," which found that talent prints are matched with linked prints of suspects in only 1 percent of all cases.

The report found that "crimes are most frequently solved as a result of information the victim is able to supply the responding patrol officer, and not as a result of physical evidence, directly traceable to a suspect."

"The fact is," said Vezzani, "in real life, the police don't often do elaborate tests. Prints are hard to lift in a good, reliable state. Those cute, sophisticated scientific tests you see on TV shows are hard, and rare."

Vezzani said he once prosecuted a case in which an injured burglar had been followed by police from a vending machine break-in to his apartment by the trail of blood he left. He was caught with the vending machine money in his possession. But the jury did not return a guilty verdict.

"When I later asked the jurors why," Vezzani said, "They answered, 'Where were the fingerprints? You didn't introduce fingerprints.' Well, who needed prints? He was caught red-handed."

Lewis said he once tried an accused drug dealer whom police had seen throwing aside a plastic bag full of heroin. "Prints just can't automatically be lifted off a plastic bag, and besides, we had eyewitnesses. We lost the case, and the jurors told me later it was because I didn't have prints," he said.

Defense attorneys, on the other hand, complain that jurors expect them not only to defend their client, but also to prove who really is guilty, as Perry Mason would. Many jurors, attorneys say, do not understand that the burden of proof rests with the prosecution.

Larry Williams, directing attorney of the Greater Watts Justice Center, said: "The most common comment we hear from jurors after a trial is, 'Why didn't you do this or that, introduce that evidence, question that witness?' Jurors just don't realize how constrained a lawyer is in what he can do. The fact is, the rules of evidence just don't allow it. Those big argumentative speeches you see on TV are good for the script, but they wouldn't be allowed in court."

Washington attorney Edward Bennett Williams has complained that television fails to recognize that the lawyer is not "the absolute factor in winning or losing a case." Of 100 cases, he estimated, the best lawyers might win 60; the worst might win 40.

When he mentions this to law students during lectures, he said, "Increasingly I sense the disblief . . . for I am addressing a generation that has matured with the examples set by television lawyers over hundreds of programs. The students seem to have accepted a point that TV's dramatists have not consciously tried to make. But almost subliminally, students have come to understand that criminal cases are decided by rhetoric . . .

"The vast majority of (real) courtroom successes . . . are built with plodding care and exploited with common-sense reasoning. Very, very few actual cases are won with dramatic appeals to a jury, sudden disclosures of proof or sly little tricks."

Lawyers also say that jurors, expecting trials to be as fast-paced and dramatic as TV shows, often grow bored and restless in the courtroom.

U.S. Court of Appeals Judge Dorothy Nelson, a former dean of the University of Southern California law school, found that more than half of a sample of 2,000 jurors were dissatisfied because of the "long delays" and "interruptions" they experienced.

Jurors seeking drama also seem to expect witnesses to look and talk like actors, the lawyers report.

"But a street patrolman may just not be that articulate," Vezzani said. "The cop or the poor robbery or rape victim may hem and haw, look at his feet. There's nothing I can do except try to prepare the jury, remind them that this real life."

Finally, some lawyers complain that they must also deal with the TV-formed expectations of witnesses and their own clients.

"Lawyers on TV are brilliant or saintly, and always getting their clients acquitted," said New York attorney Martin Garbus. "The truth is that 90 percent of all defendants are convicted, and most lawyers work for fees, not to change the world . . . They are no more less virtuous than anyone else. Clients are often angry and frustrated with their lawyer . . . when they realize he is not totally and devoutly committed to their case. There is a difference between a $250 defense, a $2,500 defense and a $25,000 defense."

Faced with all the TV-fed expectations, some investigators and lawyers have found it best simply to give jurors what they expect. They have altered their own work plattens.

Vezzani said he now asks for fingerprints even when they are not needed. Once he prosecuted a case in which police happened onto the scene of a beating and caught two men redhanded. "I confiscated their blood-splattered shoes and had the blood analyzed, then matched to the victim's blood. I didn't do this for the law -- remember, the cops saw the beating -- but because the jury would expect it," he said.

Indiana prosecutor Thomas Knight said that often when he doesn't have fingerprints, he calls a fingerprint expert to the stand anyway, to explain why there are no prints.

Lawyers say the also have to become actors and directors. David Glickman, a Beverly Hills attorney, said: "Knowing the jurors have been heavily influenced by TV, I try to make the trial dramatic . . . I use charts and enlarged photos and try to inject a little suspense. I pace things out and try to have interesting stuff both in the morning and the afternoon."

The belief by lawyer that trial participants learn about courtrooms from TV seems to be supported by a number of studies, many of them conducted by the Annenberg School of Communications at the University of Pennsylvania.

One Annenberg study concluded that "viewing of television was found to cultivate an understanding of the world of law enforcement consistent with TV's somewhat inaccurate portrayals."

Said Lewis: "It is high time that more attention was paid to the impact of TV on our system of criminal justice."

Attention is being paid, but not with the focus Lewis has in mind. Legal groups and academics seem to worry more about TV news cameras in real courtrooms than about TV's fictional dramas.

In recent years, 23 states have begun to allow still photography and television coverage of trials, either experimentally or permanently. Florida pioneered the trend with a one-year experiment in 1977; last year it made the coverage prmanent.

The trend has accelerated, but not everyone trusts the experiments' results. Particularly doubtful are defense attorney's public defenders and some social scientists.

They cite, for example, the Mark Herman murder trial in West Palm Beach, Fla., in February 1978, which attracted wide attention and gavel-to-gavel coverage.

When the jury returned a guilty verdict, many observers reportedly were surprised because the prosecution's case was circumstantial and relied heavily on testimony of jail inmates.

"You can never prove, you can only say what's possible," said the judge, Thomas Sholts, afterward. But perhaps the jurors were affected by what they thought was community pressure against the accused boy. After all, it was a case of a bad kid accused of shooting a good citizen, a family man, in his home. I can't say; I can't go inside juror's minds."

Psychological studies by a Washington state clinical psychologist, Jay Finklestein, suggest that the more "public" a person's decision is, the more likely he is to shape it toward what he believes the group thinks. Anonymity, the studies found, is important for a person to reach an independent decision.

Most recently, televised coverage was accused by some of helping to incite the Miami riots that followed the acquittal of four white policemen in the beating death of a black insurance executive.

Some Miami attorneys argued that TV stations on their evening news showed only the dramatic or violent aspects of the trial. The public, they said, did not see the same trial the jury saw, and thus could not understand the reasons for the acquittal.

Ironically, lack of definitive evidence has become the chief ammunition for both sides in the debate.

To some, the failure to identify TV's impact merely proves that much of the effect is too subtle to be measured or disconcerned. They say that TV's proponents should have to prove beyond doubt there is no adverse impact.

"You give any problems to an academic," one judge snorted, "and they can come up with questions that can't be answered. They're not dealing with reality. I'm in the real world."

But the Florida Supreme Court, after the one-year experiment ended and reports were filed, voted unaminously to make the experiment permanent.

Chief Justice-designate Alan Sundberg, who wrote the opinion, acknowledged that the surveys used for evaluation were "nonscientific and reflect only the respondents' attitudes and perceptions." Still, he said, the fears of psychological influences "are but assumptions unsupported by any evidence."

Almost all the objections on TV, Sundberg said, could be made against the print media.

Thomas Sholts, the Florida judge most vocally opposed to televised trials, said, however, "The differences between print and TV are obvious to me. TV is just more powerful. Lots of people don't read papers, but they just absorb TV by osmosis."

As might be expected, the entire controversy has once again landed before the Supreme Court. The justices have agreed to review the televised burglary conviction of two ex-police officers in Miami Beach.

The case of Chandler and Granger vs. Florida seems like to produce a landmark decision because the former police officers' attorney, Joel Hirschhorn, has drawn the issues clearly. He does not claim any specific, identifiable element of prejudicial publicity. He argues simply that the presence of the TV cameras had an adverse impact on the trial.

There is a sense among many in the legal community that the Supreme Court will finally have to base its decision on the justices' own beliefs and interpretations, rather than on definitive knowledge about impact.