THE "trial of the century" was about to break for its summer recess.

Presiding Judge Severino Santiapichi was making one last effort to decipher the mysterious, complex character of Mehmet Ali Agca, the Turkish terrorist who shot Pope John Paul II.

"You say that you are unique. You say in fact that you are the reincarnation of God," said Santiapichi, in the patient, fatherly manner that has characterized his handling of the trial.

"No, no," interrupted the pope's would-be assassin, in an equally reasonable tone of voice, as if seeking to clarify an important detail that the white-haired judge had somehow failed to grasp. "I am an angel in human form, that's all."

Such surrealistic exchanges have become commonplace in the eight-week old trial of three Bulgarians and four Turks accused of acting as Agca's accomplices in the attempted murder of the leader of 800 million Roman Catholics. The 27- year-old Turk, upon whose testimony much of the case hangs, has offered almost daily demonstrations of his unreliability as an informant. In addition to predicting that the end of the world is at hand, he has lied and contradicted his earlier testimony dozens of times.

It is tempting to conclude that the trial now underway in Rome is a judicial farce that should be brought to an end as swiftly as possible. In fact, the last few weeks of courtroom drama have succeeded in shedding considerable light on Agca's personality, the events leading up to the assassination attempt, and the pre-trial Italian investigation into allegations of a "Bulgarian connection" to the papal conspiracy.

No new information has yet come out in court to support Agca's accusations against three former Bulgarian officials in Rome whom he has depicted as his direct accomplices. Nor, apart from the inconsistencies in his testimony, has there been any conclusive evidence disproving the theory of Soviet bloc involvement. What is already clear, however, is that the hot pursuit of the "Bulgarian connection" blinded many people in the West to the possible existence of a primarily Turkish plot.

The failure of the Italian investigating magistrate, Ilario Martella, to fully explore Agca's links with other right-wing Turks has been recognized and corrected as a result of the present trial. Italian prosecutors have now opened a new investigation into Agca's proven Turkish associates, many of them childhood friends from his home town of Malatya who belonged to an offshoot of a terrorist organization known as the "Gray Wolves."

The names of most of the suspects in the new investigation have been known to police forces across Europe for several years. Some were interrogated as witnesses by Martella and have since disappeared. Others are under arrest in France, Switzerland, West Germany, and Turkey for crimes that are unrelated to the papal plot.

To be fair, it was not just the Italian magistrates who played down the Turkish dimension to the shooting in St. Peter's Square on May 13, 1981. Investigations by newspapers and television networks into the conspiracy have also tended to concentrate on the issue of Soviet bloc involvement, marshalling the arguments for and against. Preoccupied with the "Bulgarian connection," and the shadow it seemed to cast over the future of East-West relations, the press ignored the less sensational but more obvious ties between Agca and the Gray Wolves.

After more than 20 days on the witness stand, a much clearer picture of Agca's behavior under interrogation has emerged than was the case before the trial. It is also possible to detect the elements of a method in his apparent madness.

Perhaps the most striking characteristic about Agca for those who have observed him closely over the last few weeks is his curious relationship to reality. For him, the truth about a historical event is not something finite, concrete, unique. It is a marketable commodity, constantly changing according to his own particular mood and circumstances, events in the outside world and the line of questioning adopted by his interrogators.

In Agca's world, characters are assigned new lines and new roles with breathtaking rapidity. Real people rub shoulders with figments of his imagination. It is like a play with Agca as the director, author, and leading actor all wrapped into one star part. If one version of the play fails to satisfy, the plot can easily be changed and new supporting roles created.

The present trial alone has seen the appearance and subsequent disappearance from Agca's testimony of a mysterious Soviet diplomat named "Malenkov," who allegedly commissioned the assassination of the pope for the equivalent of $1.2 million. Agca has increased the number of Turkish accomplices in St. Peter's Square from one to three -- and the number of people allegedly in on the plot has expanded proportionately. Sergei I. Antonov, the only Bulgarian defendant in Italian custody, has been demoted from driver of the only getaway car to driver of a second, backup vehicle.

The trial has also provided ample evidence of the influence exerted on Agca by the mass media. He has told the court that he watches every news program that he can on the television set in his cell. His information diet is supplemented by several daily newspapers and the radio, all of which provide useful source material for his stories. Changes in his testimony are frequently provoked by something he has seen on television or read in the press.

A good example of Agca's tortuous thought process occurred the day the trial broke up for its summer recess. Suddenly, without warning, Agca retracted previous accusations against Sedat Sirri Kadem, one of the Turks who were allegedly with him in St. Peter's Square in Rome on the day of the assassination attempt. Kadem, he told the court, had had nothing to do with the plot.

When pressed to explain why he had falsely accused an innocent man, Agca replied that he had wanted the trial to end as soon as possible. He had wrongly identified Kadem, a childhood friend, in a picture of the accomplices he says were with him in St. Peter's Square in the knowledge that this claim would be shown to be false as soon a confrontation could be arranged.

Speaking as if he were deliberately seeking to undermine his own credibility, Agca went on ingenuously: "When it is verified that the man in this photo is not Sedat Sirri Kadem, then that could also arouse some suspicions about the involvement of the Soviets and the Bulgarians in the plot. You could reach the conclusion that the Soviet Union was not involved in the assassination attempt . . . it is possible that Ali Agca has told some other untruths."

Further questioning revealed that Agca had decided to incriminate Kadem, a left-wing terrorist, when he learned that he was in prison in Turkey. His decision to absolve him, he explained, came after he heard from an Italian television news program that the Turkish authorities had released Kadem. With Kadem out of prison, and possibly in hiding, it would obviously be much more difficult for the Italian court to interrogate him on his presence in St. Peter's Square.

The incident in itself tells us little about Kadem's guilt or innocence. What it does demonstrate is Agca's ability to change his story at will according to what is happening in the outside world or what he thinks his listeners want to hear. The point became even clearer a few moments later when, after the normally patient judge had lost his temper, Agca simply reintroduced his one-time friend into the plot.

Asked about obvious differences in appearance between Kadem and his presumed accomplice in St. Peter's Square, he replied blithely: "Anyone can change the way they look."

Agca's appetite both for news and exposure in the media, which he was able to indulge during a sensitive period of the pre-trial investigation when he was theoretically being held in strict isolation, has almost become a standing joke in court. People, places, and events mentioned in the newspapers have a tendency to show up in his testimony a few days later. He cites the press to support his argument that the Kremlin is threatening his life or that the Vatican wants a political solution to the trial.

Sorting out the truth from the fiction in Agca's testimony is somewhat akin to penetrating a series of Chinese boxes. The investigator is encouraged to feel that he is making progress when he succeeds in dismantling one set of lies. But then he discovers that what has been revealed is merely another set of lies mixed, as before, with some tantalizing details that appear to be accurate.

It is a world of total confusion in which, to quote Judge Santiapichi, Agca has "said everything and the opposite of everything." It is reasonable to assume that even his explanations for why he has been telling lies themselves contain an element of truth and an element of falsehood. The pope's would-be assassin may not be much of a marksman (he failed to kill his scarcely moving target from a distance of several yards), but he is certainly an expert at misleading investigators.

So complex is Agca's "double game" (one of his favorite phrases) that when he implies that he is destroying his credibility to let the three accused Bulgarians off the hook, for all we know it could be his Turkish friends that he is really concerned about. Or he may just be a pathological liar. We have no way of telling.

In this situation, the only sensible way of proceeding is to rigorously check each and every detail provided by Agca. Only those details that have been positively corroborated can be accepted as valid testimony. To believe anything that Agca says that has not been independently confirmed is to risk introducing subjective judgments into the investigation.

Yet this is precisely the trap Italian magistrates fell into during their three-year pre-trial investigation. Impressed by Agca's ability to provide a number of accurate details about the personal characteristics and movements of his alleged Bulgarian accomplices, they were prepared to believe his uncorroborated testimony about the presence of the Bulgarians in St. Peter's Square on the day of the assassination attempt and their role in setting up the plot.

The authorities continued to give Agca the benefit of the doubt even after it was shown that some of the details he supplied about the Bulgarians were false while others could have been acquired in the course of the investigation itself.

The growing skepticism of Italian magistrates about Agca's story has been reflected in the statements of Antonio Marini, the public prosecutor at the present trial. After Agca disrupted the beginning of the trial by claiming to be Jesus Christ, Marini still defended the credibility of his star witness: "When Agca begins to talk about facts," he assured journalists, "he is extremely reliable." Five weeks later, the prosecutor conceded publicly that the "Bulgarian connection" was "full of black holes." All that could be proved for certain at this stage of the trial, he went on, were Agca's links with right-wing Turks.

The pope's would-be assassin can be shown to have had extensive dealings with Gray Wolves in Austria and Switzerland in the months leading up to the assassination attempt. Documentary proof for these ties rests not merely on Agca's own contradictory statements -- as is the case for the Bulgarians -- but also on the testimony of his former associates and the statements of independent witnesses. Some of this evidence was ignored by Martella even though it was available to him.

In March 1984, for example, Martella interrogated a Gray Wolf by the name of Yalcin Ozbey who knew Agca well both in Turkey and western Europe. Ozbey gave an entirely different version of what happened in St. Peter's Square to that provided by Agca, depicting an essentially Turkish conspiracy rather than a Bulgarian one. But there is scarcely any mention of his testimony in Martella's final indictment.

Most of Agca's Gray Wolf associates fled Turkey after the September 1980 military coup, rebuilding their terrorist network in western Europe. These people provided Agca with shelter, money and occasional work, as well as helping him procure the weapon with which he was later to shoot the pope. Until the advent of the "Bulgarian connection," they were prime suspects in the papal conspiracy.

Among the Gray Wolves now wanted for questioning by Italian investigators in connection with the papal plot are Mehmet Sener, Abdullah Catli, Mahmut Inan, Eyup Erdem, and Omer Ay. All five men are proven associates of Agca but were cleared by Martella, who brought charges only against people named as his accomplices by the pope's would-be assassin.

Agca did, it is true, name three right-wing Turks in his pre-trial testimony. All three are now defendants in Rome along with the Bulgarians. But only one member of this trio -- Oral Celik, who is being tried in absentia -- can be described as a really close friend and associate of Agca. And since Celik has been in hiding ever since the assassination attempt, there seems little prospect at present of his being made to answer Agca's accusations.

Suspicion that the pope's would-be assassin is continuing to cover up for his real accomplices was voiced by Judge Santiapichi on the day the trial recessed. After listening to Agca's story about Kadem, the judge commented drily: "Somebody could conclude that you accuse your Turkish friends of complicity in the assassination attempt only when you know that your declarations can later be shown to be false."

One reason the hypothesis of a Turkish conspiracy against the pope has been taken less seriously than the "Bulgarian connection" is that the motive is more difficult to understand, particularly in the United States. The interest of the Soviet bloc in eliminating Pope John Paul II, who provided the spiritual inspiration for the social and political upheavals that shook his native Poland between 1980 and 1981, is obvious. But why would a bunch of kids from eastern Turkey want to kill the Polish-born pontiff?

Part of a possible answer to this question is contained in Agca's own personality. A child of the Turkey of the '70s, with its political tensions and wide disparities of wealth, he seems to have regarded terrorism as a shortcut to fame and fortune. It was both a way of escaping a desperately poor family background and of getting his revenge against an oppressive and unfair society.

The rest of the answer lies in the way the pope is associated by some Turks, particularly those on the extreme right who resisted Kemal Ataturk's reforms after World War I, with undesirable western influence in Turkey. As head of the Catholic Church, John Paul II is the direct spiritual descendant of the leaders of the medieval crusades against the Turks and the Moslem world. For fundamentalist Turks, the pope is the symbol of a corrupt western society.

Agca first threatened to kill the "pope-commander of the crusades" in November 1979 during a visit to Turkey by John Paul II. In an interview with Italian television shortly before the present trial, he said he had regarded the pope as "the incarnation of capitalism."

A Turkish motivation for the assassination attempt on the pope was generally accepted as plausible immediately after the shooting in St. Peter's Square in May 1981. After Agca began to point the finger at the Bulgarians in 1982, it was gradually forgotten. Now, once again, Agca's Turkish associates are the subject of an Italian investigation.

If the papal conspiracy was essentially limited to Turks, how then did Agca obtain incriminating personal details about his alleged Bulgarian accomplices? It was his ability to recite these details -- which included knowledge about their habits and movements -- that convinced Italian magistrates that he had had dealings with the three Bulgarian accused. From there it was a short step to believing Agca when he claimed that the Bulgarians had also been involved in the plot.

There are numerous chinks, however, in this chain of logic. Agca's initial descriptions of the Bulgarians -- before he was allowed to see their photographs -- were wildly inaccurate. The knowledge that he displayed about his alleged accomplices grew gradually as the investigation proceeded. His contacts included regular visits from a Catholic friar now accused of being a member of the Mafia and conversations with a Red Brigades terrorist in the adjoining cell.

The papal conspiracy trial is of course far from over. It is likely to go on for at least a year, during which time more than 100 witnesses will be heard. It is quite conceivable that new, more convincing evidence will emerge against the Bulgarians -- offsetting the knocks that Agca's credibility has taken in the opening weeks.

In the meantime, however, it is worth remembering that there is an alternative to the "Bulgarian connection" that has received so much attention in the press over the past three years. For the moment, it remains just a hypothesis that must be proved in court. For want of a better expression, let's christen it "the Turkish connection."