The story of the plot to kill the pope begins in this city where Europe meets Asia, the historic crossroads between East and West.

The date: June 25, 1979. The scene: the Marmara cafe, a right-wing student haunt on the European side of the Bosporus. Suddenly the police burst in, cornering a scruffy, 21-year-old youth who is nonchalantly playing cards.

"I did it. I acted alone," the youth readily confesses when charged with the sensational assassination of Turkey's most prominent newspaper editor. Sent to the country's most secure military prison, he manages to escape precisely five months later.

A year and a half after the youth's escape, the scene shifts to St. Peter's Square in Rome, where the spiritual leader of 800 million Catholics is holding his weekly open-air audience. There is applause as Pope John Paul II, riding in an open jeep, stretches out his arms in greeting. Suddenly two shots ring out above the crowd, hitting the pope in the shoulder and abdomen.

The cheers turn to screams. Despite the pandemonium, the gunman is caught. He boasts to his interrogators: "I acted alone."

It is now known that Mehmet Ali Agca did not act alone -- either in Istanbul or in St. Peter's Square. Later this month, after an investigation of more than three years, an Italian judge is expected to issue formal indictments against up to eight alleged accomplices in a plot to murder Pope John Paul II on May 13, 1981.

The suspects are said to represent an amalgam of backgrounds as strange as any John le Carre novel: a gang of right-wing Turkish political thugs, an international smuggling ring known as the "Turkish mafia" and the Bulgarian secret service. Pulling the strings in the background, according to the Italian state prosecutor, was a mysterious "politician of great power" who allegedly plotted the assassination of the Polish-born pontiff in order to safeguard "the higher needs of the Soviet Bloc."

Much of the evidence in the papal conspiracy case comes from Agca himself. Running into thousands of individually signed typewritten pages, his confessions provide the key element in attempts to demonstrate that the plot to kill the pope can be traced ultimately back to the Kremlin.

The question of Agca's credibility is likely to dominate the forthcoming trial. The prosecution is expected to maintain that, despite some acknowledged lapses, the pope's would-be assassin has earned the right to be believed after providing accurate details about his alleged co-conspirators. The defense can be expected to maintain that the prosecution's star witness has lied so often that his testimony is worthless.

The first two articles in this series will attempt to shed as much light as possible on Agca and his times by tracing the path that brought him face-to-face with Pope John Paul II in St. Peter's Square. Subsequent articles will describe the Italian investigation into what has become known as the "Bulgarian connection."

The reporting for this series was conducted in Italy, Turkey, Bulgaria, West Germany and France. It is based on Agca's statements, court documents from both Italy and Turkey, interviews with Italian and Turkish investigators, interviews in Bulgaria with three of the principal suspects, and an examination of all available published material about Agca. East-West Context

It was perhaps inevitable that the attempted murder of the first Polish pope in history should spawn a rash of conspiracy theories. Given the fact that it occurred as Poland was in the midst of what amounted to a peaceful insurrection against Communist rule, it was also easy to predict that the affair would become inextricably tied up with the ideological struggle between East and West.

Details that have filtered out of interlocking judicial investigations in both Italy and Turkey during the past few months suggest that the truth is more complex, but also more fascinating, than the one-dimensional picture that has been presented by commentators of both left and right. What emerges is not a definitive conclusion but a series of significant pointers:

Agca associated closely with a group of youths from the Malatya region of eastern Turkey loosely connected to a right-wing terrorist organization known as the Gray Wolves. Until the declaration of martial law in Turkey in September 1980, this group operated almost entirely inside the country. After the military takeover, many of its members fled to Western Europe.

There is convincing evidence that the Malatya subgroup of the Gray Wolves killed the prominent Turkish newspaper editor, Abdi Ipekci, in Istanbul in February 1979. Agca first confessed to this murder, but he now has retracted this confession. Who actually killed Ipekci is still unknown.

Following his escape from prison in Turkey, Agca went first to Iran and then to Bulgaria. He can be shown to have had some contact with members of the "Turkish mafia," a ring of politically well-connected smugglers who operated through Bulgaria with the apparent connivance of the Bulgarian authorities.

There are many similarities between the murder of Ipekci and the attempted assassination of the pope. In both cases, Agca appears to have acted as the protege of a more influential Gray Wolf from Malatya named Oral Celik. Under interrogation, Agca behaved in a similar way in both Turkey and Italy, changing his testimony repeatedly in an apparent attempt to protect his immediate associates.

Italian investigators have failed to turn up independent evidence that directly links the pope's would-be assassin to the three Bulgarian officials accused of being his co-conspirators. Agca's credibility as a witness has been questioned publicly by other magistrates, both in Italy and in Turkey.

A necessary backdrop to the story is provided by dramatic events that took place at the turn of the decade. The upheavals in the pope's native Poland were sending ripples of fear and excitement around the Soviet Bloc. Turkey, a key U.S. ally that straddles Europe and Asia, seemed to be on the brink of civil war -- with arms and ammunition being smuggled to both sides via its Communist neighbor, Bulgaria.

Italy, recovering from a wave of terrorism, was in the grip of a series of judicial and political scandals, each more titillating than the last. The secret services were in disarray, a shadowy Masonic lodge known as "P2" was found to have infiltrated the political establishment, and the Vatican's own bank was caught up in a financial swindle.

Onto this stage strolled Agca -- a product of the economic and social tensions that welled up in Turkey in the 1960s and '70s, a man whose most notable quality is his capacity for deception. Shaped by '70s

Born in 1958, Agca was brought up in the town of Malatya, capital of Turkey's most backward and easternmost province. His father, who was by many accounts a rough character, died when he was 8. As the oldest of three children, Mehmet Ali helped his mother eke out a living by selling water at a railway station to passing train passengers.

The Agca family had settled in one of the outlying shantytowns of Malatya called Yesiltepe. It was in the Yesiltepe high school that Mehmet Ali, then an impressionable 15-year-old, first came into contact with the Gray Wolves -- the militant youth wing of the extreme right-wing National Action Party.

"Agca is a very Turkish monster," said Haluk Sahin, editor of the country's most prestigious weekly news magazine, Nokta. "In order to understand him, you also have to understand the Turkey of the '70s. These were the years of social frustration and disappointment that followed the rapid economic growth of the '60s. For a Turkish youth, joining a terrorist movement was like acquiring an identity -- almost the equivalent of joining a sorority for a kid in the States." Recent sociological studies in Turkey have shown that left- and right-wing activists shared very similar attitudes. For most young Turks, Agca included, membership in a political clan was more a matter of chance and social compulsion than deep-rooted personal conviction.

"It was like that in those days," said Yalcin Ozbey, a close associate of Agca who is also from Malatya, when asked to explain why he became a Gray Wolf. He was interviewed in West Germany, where he now lives. "There was a kind of blood feud going on. You were practically forced to join one side or the other."

This was the period in Turkey when a high school student might kill a teacher or government official merely to demonstrate his virility to his companions. The violence was particularly intense in the Malatya region, where an average of two or three murders were committed every day.

The main factor that caused Agca to fall in with the Gray Wolves was that they happened to control the part of town where he lived and went to school. A second consideration may have been the fact that he was a Sunni Moslem and many Sunnis tended to be rightist, if only to set them apart from the rival Alawis, who were generally leftist.

Fueling the political agitation in Malatya was the province's economic backwardness at a time when large disparities in wealth were becoming increasingly visible thanks to television and modern communications. According to Ismail Kovaci, a Turkish journalist who has researched Agca's background, this feeling of resentment spawned a desire to find a short cut to fame and worldly success.

"Agca suffers both from jealousy and delusions of self-grandeur. For him, terrorism represented a way of leaving his mark on the world," Kovaci said.

Many people who encountered Agca both in Turkey and in Italy have spoken of his "Carlos complex" -- his image of himself as a top-flight international terrorist with the whole world hanging breathlessly on his every word. His desire for personal publicity seems unquenchable. At one point in the Italian investigation, he abruptly clammed up when the magistrates refused his demand that journalists be present as he "confessed." Ersatz Exam

As a youngster, Agca thought of becoming a teacher. By the age of 18, he had abandoned this idea. According to his family, he said that a teacher's salary of roughly $250 a month was not for him. In the fall of 1976, he enrolled in the history and geography department of the University of Ankara, staying in a rightist-controlled dormitory.

The extent of Agca's own involvement in the bitter political clashes that dominated student life during this period is not clear. In testimony to Italian magistrates, he later stated that in the summer of 1977, he traveled to Syria and Lebanon with the help of Turkish left-wing terrorists for training in Palestinian refugee camps. No concrete evidence ever has been found to support this claim, which is dismissed as "not serious" and "abstract" by the Turkish military prosecutor investigating the Ipekci murder.

What can be demonstrated, however, is that in 1978, Agca succeeded in transferring to the economics department of the University of Istanbul, thanks to a friend who took the entrance examination on his behalf.

Proof of the fraud turned up only later, after the attempted murder of the pope. Agca consistently has refused to tell investigators the name of the friend who helped him and still insists that he took the exam himself. What is revealing about the incident, in the words of the Turkish military prosecutor who investigated it, is that it provides an early sign of Agca's "ability to deceive."

Coinciding with the affair of the faked exam papers is a string of mysterious bank deposits made in Agca's name in Istanbul and Malatya. Between December 1977 and January 1979, a total of 360,000 Turkish lire (about $15,000 at the exchange rate then) had been secretly paid to Agca -- an incredible sum for a supposedly penniless student.

After at first refusing to reveal the origin of this money, Agca now says it came from a black-market smuggling operation that he and a group of friends organized in the Beyazit and Aksaray districts of Istanbul. The aim of the operation, he told Turkish magistrates who visited him in Italy, was to fund a political organization to "undermine the western democracies," including Turkey.

By Agca's account, the "organization" consisted of a group of youngsters from the Malatya region of eastern Turkey. Most of them have been identified since in one way or another with the Gray Wolves: Oral Celik, Yalcin Ozbey, Mehmet and Hasan Sener, and Yavuz Caylan.

Agca's explanation of the source of the funds has been accepted as a plausible, if so far unproven, hypothesis by the Turkish military prosecutor investigating the Ipekci murder. 'The Godfather'

The complex and controversial relationship between the Gray Wolves, ostensibly a political organization, and the loosely knit band of smugglers known as the "Turkish mafia" is central to the mystery of whether Agca and his friends were manipulated by outside forces. It has been studied closely by Turkish and Italian investigators seeking clues both to Ipekci's still unsolved murder and the attempted assassination of the pope.

During the '60s and '70s, smuggling of all kinds of goods, from cigarettes and coffee to copper and guns, became a vast organized business in Turkey. The overprotected domestic economy was in a state of chaos, corruption was rampant, and import and export regulations were strangled in red tape.

In a country renowned for its smugglers, Abuzer Ugurlu was known as "the godfather." Like many of the people in this story, he too was born in Malatya Province, the scion of a family of smugglers. By the time he had reached his late thirties, he was wanted in half a dozen European countries on suspicion of being the linchpin in a huge illicit trade of arms, cigarettes and narcotics to and from Turkey.

Much of Ugurlu's business seems to have been conducted through Bulgaria, a country that straddles Turkey's transportation lines with Western Europe. According to testimony provided by fellow smugglers, he illegally imported tens of thousands of weapons into Turkey with the active connivance of the Bulgarian authorities -- a crime for which he was convicted in 1974 and later released under a Turkish government amnesty.

To carry out this large-scale smuggling operation, Ugurlu also needed agents in the Turkish customs ministry. It is now known that key customs posts were infiltrated by supporters of the extreme right-wing National Action Party, the political wing of the Gray Wolves, during the late '70s.

It was a self-serving kind of relationship. Ugurlu's interest was making money -- but he needed political protection to cover his smuggling activities. The National Action Party, whose leader, Col. Alparslan Turkes, served as deputy prime minister in successive conservative-led coalition governments between 1975 and 1978, needed funds to pursue political aims.

Ugurlu is now on trial in Turkey on charges of helping to plan Ipekci's murder and assisting in Agca's escape from prison by providing financial support to his group. Evidence for Ugurlu's involvement in the Ipekci murder rests largely on Agca's own testimony in Rome. Agca's assertion that he and his friends received funds from the "godfather" is to some extent supported by the fact that Ugurlu can be shown to have authorized a payment of 2,000 West German marks (then about $800) to Agca in Bulgaria in July 1981.

It is now up to a Turkish court to decide whether Agca is telling the truth when he claims that Ugurlu was involved with his group well before the Ipekci murder. The godfather" repeatedly has denied ever meeting Agca. He has acknowledged, however, that he had contacts with other Gray Wolves and even visited them in Istanbul's Kartal-Maltepe military prison. His hometown, Poturge, was also the birthplace of Agca's close friends, the Sener brothers, and it is quite conceivable that the two families knew each other.

The contacts that Ugurlu, then 36, can be shown to have had with individual Gray Wolves raise the question of the nature of this relationship. Which side was pulling the strings?

Proponents of a "Bulgarian connection" to the papal plot have argued that the bosses of the Turkish mafia used Gray Wolves like Agca to do their dirty work and were in turn used by the Bulgarian secret service. When the Bulgarians needed a hit man to kill the pope, according to this theory, they asked the mafia to act as intermediaries. Agca, with his ready-made "right-wing" persona, was the ideal man for the task.

This version has been disputed by independent Turkish researchers such as Orsan Oymen, formerly chief investigative reporter for Milliyet, Ipekci's newspaper, and a leading authority on Agca.

"My opinion is that it was the other way around. It was the Gray Wolves who were in a position to ask favors from the mafia. They were the ones with the political influence at the time, because of their control over the customs ministry," Oymen said in an interview in Bonn, where he now works as the paper's correspondent in West Germany.

Ugur Mumcu, an independent left-wing columnist and lawyer who has done more than anyone else to expose Bulgaria's involvement in the smuggling of arms to Turkey, takes a middle position.

"You can prove that Agca had two kinds of links. He had ties with the Gray Wolves and he was also connected to the smugglers. The nature of both these links should be thoroughly investigated," he said in his office in Ankara. Editor Killed

Abdi Ipekci was murdered on the evening of Feb. 1, 1979, as he drove home from his office in Istanbul. According to the official police report, five cartridges from a 9-mm pistol were found at the scene.

Ipekci's assassination marked a dramatic twist in the rising spiral of political violence. His newspaper, Milliyet, had been regarded as a leading voice for tolerance and national reconciliation. His death seemed to be confirmation that there was no place left in Turkey for political moderates.

Agca's testimony about the Ipekci murder has gone through various transmutations -- each version contradicting elements of the previous one. The tactics he employed with his Turkish interrogators provide a curious foretaste of the way he was later going to behave in Rome when questioned about the attempted assassination of the pope.

In Turkey, his initial reaction was to say that he alone had murdered Ipekci. He then admitted that he had accomplices -- but assigned them a slightly different role in the plot with each successive interrogation. He now claims that he did not kill Ipekci at all but took the blame to cover up for his friends.

Mumcu, who has made a careful study of how Agca's testimony evolved from day to day, says that by confusing his interrogators, Agca succeeded in covering up the evidence and allowing his real accomplices to get away.

In his book, "Pope, Mafia, Agca," Mumcu has shown that Agca must have been able to communicate with another Gray Wolf, Yavuz Caylan, who had been arrested as a suspect in the case and held in the same prison. When one of them changed his evidence about what became of the murder weapon or who took part in the crime, the other did, too.

Mumcu's allegations about the way in which Agca coordinated his testimony with Caylan have since been repeated by Agca himself. In his most recent statement to Turkish investigators in Rome, Agca boasted: "We applied this plan when we were both locked in the cells of the Istanbul police headquarters. Even under such conditions, we could communicate."

Agca is depicted by Mumcu as "a master liar" whose proficiency at deception is helped by "the gullibility of people who want to believe him . . . . "He mixes truth with fiction. Everything he says must be checked," Mumcu insists. Sheltering Wolves ------------ Soon after his arrest for the murder of Ipekci, Agca began bragging to a Turkish military judge that the mandatory sentence of death "will never reach me." He kept his word. On Nov. 23, 1981, he escaped from the heavily guarded Kartal-Maltepe military prison outside Istanbul in the uniform of an Army private that had been provided to him by a guard.

The mechanics of Agca's escape from prison provide important pointers to the identity of his close accomplices. Practically everybody who assisted in his escape, who later hid him in Ankara, and then supplied him with a false passport to travel to Iran was associated in one way or another with the Gray Wolves. Many of them came from Agca's own region of Malatya.

A prison guard, Bunyamin Azeryilmaz, has confessed to Turkish magistrates that he led Agca out of the prison in return for a $4,000 bribe and because they both shared "rightist views." After walking through half a dozen security checkpoints late at night, the two men caught a bus across the Bosporus to the center of Istanbul.

According to Turkish court documents, the key role in organizing the escape was played by Agca's Malatya friend, Oral Celik. Born in 1959, Celik is a year younger than Agca -- but in many ways seems to have been like a father to him. Whenever Agca was in trouble, he turned to Celik for help.

Several Gray Wolves, including Agca, have testified that it was Celik who arranged for money and guns to be smuggled into Agca in prison, Celik who sent him to Ankara by car when things were getting too hot in Istanbul, and Celik who later made arrangements for Agca to seek refuge for two months in Iran, then in the throes of its Islamic revolution. Agca has now accused Celik, along with Yalcin Ozbey, of killing Ipekci.

The picture that emerges from court documents and testimony by Agca's friends is of an organization within an organization. The Gray Wolves have been depicted as the paramilitary youth wing of the neofascist National Action Party led by Col. Turkes. In fact, the command structure seems to have been a loose one, allowing plenty of room for semiautonomous factions and groups that did not necessarily take their orders from the top.

The group to which Agca belonged was largely made up of youths from the Malatya region -- a part of Turkey known for its tightly knit personal relationships. It was this group, which looked to Celik as its leader, that carried out the murder of Ipekci, according to the report of the Turkish military prosecutor. Members of the group were later to reappear in Western Europe prior to the assassination attempt on the pope.

Three days after his escape from prison, Agca wrote a letter to Milliyet, the late Ipekci's newspaper, threatening Pope John Paul II, who was about to pay a visit to Turkey.

Couched in language that bears a marked resemblance to editorials that appeared in extreme right-wing newspapers at this time, Agca described the pope as "the commander of the crusades" against Islam and went on: "If this visit . . . is not canceled, I will without doubt kill the pope-commander."

This letter has been interpreted in different ways. Some Turkish investigators like Oymen believe it suggests that Agca was thinking about killing the pope as early as 1979 -- before his controversial trip to Bulgaria in mid-1980. The Italian prosecutor, however, has accepted Agca's own contention that the threat was designed as a diversion to ease his own escape from Istanbul by focusing police attention on the person of the pontiff.

NEXT: The road to St. Peter's