Ronney Albert Zamora, 15, sits in the courtroom watching his own trial for murder as impassively as a child watching television. This time, however, television was watching him.

Thousands of people in Miami, Fla., were able to see daily excerpts from Zamora's trial, taped in the courtroom as it happened, on public TV station WPBT last fall. Now some of the taped footage is being made available to a much wider audience through "TV on Trial," a hugely imperfect and highly important documentary on Channel 26 at 9 o'clock tonight.

It is unusually worthwhile viewing if only because it raises innumerable haunting issues that are going to come up again. In fact, it is something of an issue in itself.

Zamora was accused and convicted of murdering an elderly neighbor while he and a friend were caught in the act of burglarizing her home. Zamora's lawyer, Ellis Rubin, chose a sensational defense, maintaining that the youth was a victim of his environment - illegitimate, raised by strangers, unable to speak English when he came to the United States from Costa Rica - and that television was an inordinately large part of that environment. His mother testified, for instance, that he learned to speak English from watching TV.

When discovered by the neighbor, Elinor Haggart, Zamora pulled the trigger on a gun found in her home and killed her - acting out what prolonged exposure to TV violence had conditioned him to believe was normal behavior, the lawyer maintained. Partly because Rubin himself is a shameless dramatist, media shorthand reduced this defense to "television intoxication," and by titling their documentary "TV on Trial," the producers only compound an oversimplification.

WPBT's camera was allowed into the courtroom to observe everything but whispered asides between judge and lawyers as part of a one-year test program approved by the Florida Supreme Court. Whether this experiment will eventually lead to cameras in the courtroom across the country remains to be seen. The arguments could go on for years.

The specifics of this case aside. Florida viewers were able to witness an invaluable demonstration of the mechanics of the judicial system as they watched most of each day's proceedings in their homes. By editing the original 27 hours of broadcast trial down to less than two hours of tape for PBS, the producers of "TV on trial" make the demonstration considerably less invaluable. Yet many viewers will be struck and instructed by the differences between a real trial, even in fragments, and the artificial versions that have been the stock in trade of melodramas on stage and screen.

One of the most obvious, if superficial, differences is that the lowliest Hollywood art director in the world couldn't have come up with a courtroom as homely and schizy with gingerbread as the one in which most of the trial took place.

"TV on Trial" executive producer Shep Morgan says he wanted to do as comprehensive a report on the trail as we could," but in two hours, that's a pretty hopeless goal, expecially since this trial has three fascinating aspects: the unprecedented use of TV viewing as part of a temporary insanity defense, the televising of the trial itself, and the case history of Zamora, who may or may not be the logical; tragic extreme of a generation for whom fraudulent fantasy is rarely more than an arm's reach way.

A psychiatrist testified at the trial that after the gun had gone off, Zamora was surprised that "there were no screams like he had seen on TV, and (so) to him, it did not seem real."

Some wasteful decisions were made in putting the documentary together. One was in trying to convey the chronological history of the crime itself through the testimony of witnesses. The narrator could have summarized this information in a few sentences. The program fritters away its first half-hour until Zamora's mother takes the stand and testifies that her son's immersion in television led him to suggest that his stepfather "shave his head like Kojak."

The portrait of an incredibly lonely and alienated boy (who had witnessed the drowning of a schoolmate the year before) is continued by psychiatrists Rubin attempted to call as witnesses. Judge Paul Baker, more attentive and acerbic than he seems in this condensation, would not allow testimony about the effects of TV viewing generally, and we see him concurring with the prosecution's objection to this testimony in the documentary.

What was omitted in the editing was Baker's later rebuke to a prosecuting attorney over a further objection to another psychiatric witness: "I am not about to sit here and rob a 15-year-old boy of his defense. "I'm just not going to do it," Baker said.

Such false impressions are inevitable in this kind of documentary, and the producers admit them. The unbearably pompous host they chose, journalist Richard Reeves, tells viewers that "more than 1,000 edits" were made in the trial tape and tells us, "You're going to be manipulated to meet the needs of television." Wrong. We are not going to be manipulated unless we let ourselves be manipulated. It's the truth that's being manipulated to meet the needs of television.

Only one camera was allowed in the courtroom (in addition to a much noisier and more obtrusive still camera from a local newspaper), and it could only focus on one area at a time - the jury box, the witness box, or whatever. In producig the documentary, reaction shots have been inserted out of sequence in order to visually enliven the program.

So every time there is a "cut" to another person during testimony or other courtroom activity, the image lies. By the end of the program, when Zamora is being sentenced to life in prison, we can't be sure if the shot of him staring passively ahead was really his reaction to the sentencing or something plucked from some other part of the proceedings.

From Miami, Morgan says in defense of this practice that the shots used are "very close in proximity to the actual shot" in time; it wasn't as if he grabbed a moment from one day of the trial and dropped it into another day, he said. The practice was necessitated partly by the objections of PBS engineers and technical personnel, who considered this a "marginal" program because of poor picture and audio quality. Leave it to the engineers. They will find ways to ruin good television that everyone else overlooks.

That this kind of manipulation is possible, however, stands as an argument not against TV coverage of trials but against being able to play around with the resulting footage once the trial is over. This documentary may unwittingly represent the most dangerous precedent established in Florida's experiment into liberating the courtroom. On the other hand, "TV on Trial" still affords a riveting, iluminating look at the judicial process and a significant murder trial, and it is obvious that, despite such unnecessarily glitzy touches as the jazzed up opening credits, the producers - Morgan and Dan Fouser - made a conscientious effort at telling the story as faithfully and fully as myriad restrictions and handicaps would allow.

The only really unforgivable element is Reeves, another strutting professorial pedant who has elected himself national expert on television. Reeves recently wrote a childishly hysterical fantasy about Fred Silverman that was passed off as analysis in Esquire. When, near the end of "TV on Trial," Reeves looks hard into the camera and says, "I think I know something about this medium," you yearn for Judge Baker to appear and rule him eitther out of order or off his trolley.