Italian judicial authorities turned over to defense lawyers today evidence that a Bulgarian official accused of having plotted with a Turkish gunman to kill Pope John Paul II in May 1981 repeatedly contradicted himself in providing an alibi for the day of the assassination attempt.

The flawed alibi is disclosed in a 1,243-page indictment against three Bulgarians and five Turks that contains the full results of a three-year investigation concluding that there was a "Bulgarian connection" in the shooting. The full document, which has been kept a closely guarded secret, was obtained by The Washington Post.

The indictment outlines the Italian state case in what will certainly be one of the most sensational criminal trials ever held. It depends heavily on the testimony of would-be papal assassin Mehmet Ali Agca and a mass of circumstantial evidence pointing to a relationship between him and the accused coconspirators.

Describing the attack on the pope's life as "a monstrous crime against the whole of humanity," chief investigating magistrate Ilario Martella lends credence to charges by Agca that he acted with the support and encouragement of Bulgarian officials in Rome and a Turkish businessman closely tied with the Bulgarian authorities. But he stops short of outlining a motive for the plot, which an Italian public prosecutor earlier depicted as designed to suppress political and social upheavals in the pope's native Poland.

Agca was arrested immediately after the attack on the pope shortly past 5 p.m. on May 13, 1981, and was sentenced to life imprisonment that July. He has also been convicted in his native Turkey of the murder of a newspaper editor.

Martella has explained his unwillingness to draw political conclusions from the evidence gathered in his report by saying that this was not his job. At a press conference Friday at which he outlined the contents of the indictment, he said that he had "stuck to the facts."

Martella's full indictment adds some previously unknown details about Agca's stay in Bulgaria in July 1980 as well as outlining the case that a second Turk fired on the pope on the day of the assassination attempt. The thrust of the evidence, however, is very similar to that contained in a 77-page report filed in court earlier this year by the public prosecutor, Antonio Albano.

The indictment makes clear that the Italian judicial authorities have failed to find any independent witnesses willing to testify that Agca ever met with any of the three Bulgarian defendants. Evidence for a relationship between the accused Bulgarians and Agca rests on the ability of the pope's would-be assassin to provide a number of accurate details about their movements, facial characteristics and personal habits.

Judge Martella rejected the claims of the defense attorneys for the Bulgarians, who have asserted that Agca could have been fed these details either before or after his arrest. He also rejected theories put forward by the Italian press that Agca may have been encouraged to give evidence against the Bulgarians by members of the Italian secret services who visited him in his prison cell in December 1981.

Martella acknowledged, however, that Agca's testimony includes a series of contradictions, retractions, exaggerations and falsehoods. He described as "grotesque," for example, Agca's claims that he discussed committing terrorist actions in the United States with the assistant military attache at the Soviet Embassy in Tehran.

The report quotes from statements by Agca about the assassination attempt itself in which he said that he was acting in coordination with a Turkish friend, Oral Celik. He said that, after firing at the pope, he had planned to run out of the square to a car driven by one of the Bulgarians but was grabbed by the crowd.

The driver of the getaway car, according to Agca, was Sergei I. Antonov, an official of the Bulgarian airline Balkanair and the only one of the Bulgarian defendants held in custody in Italy.

Agca recognized Antonov and the two other accused Bulgarians from an album of 56 photographs shown to him on Nov. 8, 1982. Martella has told The Washington Post that all the photographs in the album were of Bulgarians in Rome but maintains in his report that the pope's would-be assassin did not know why he was being shown the album.

The indictment contains a number of details that are likely to become the subject of heated legal arguments at the forthcoming trial. They include the following: Alibis for Antonov: Martella wrote that Bulgarian employes of Balkanair changed their testimony in an apparently coordinated attempt to give Antonov a cast-iron alibi for the afternoon of May 13.

According to court records cited by Martella, Antonov first could not remember where he was at the time of the assassination attempt. He later produced a precise account of how he had spent the entire afternoon at the offices of Balkanair, including a description of the "emotion felt by everybody" when another Bulgarian allegedly phoned with news of the attempt on the pope's life.

Martella quoted Antonov as saying initially that he remembered watching television news accounts of the assassination attempt on the pope with his wife, Rositza. The Bulgarian later changed his story, saying that his wife had not even been in Rome at the time. Alibi for embassy administrative officer Todor S. Aivazov: Bulgarian Embassy defense lawyers have said that Aivazov could not have attended a "dress rehearsal" of the assassination attempt in St. Peter's Square, as claimed by Agca, on May 12, 1981, as an Italian customs official had sworn that he was in his company.

Martella depicted the customs official, Maurizio Lucchetta, as an "extremely confused" and unreliable witness who had contradicted himself repeatedly. He wrote that Bulgarian witnesses appeared to have coordinated their testimony among themselves to help Aivazov. Agca's stay in Bulgaria: Martella's report disputes documentary evidence furnished by the Bulgarian authorities showing that Agca, traveling on a false Indian passport in the name of Yoginder Singh, was in Bulgaria from July 23, 1980, to Aug. 31, 1980. Agca has maintained that he arrived in Sofia in the first week of July.

Martella wrote that Agca's account was supported by the fact that he claimed to have met a Turkish businessman named Omer Mersan, closely connected with a gang of smugglers operating through Bulgaria. The Bulgarian authorities have submitted documents to Martella claiming that Mersan was not in Sofia at the beginning of July, but his passport shows that he was there from July 4 to July 5. Knowledge of English: Agca has claimed that his Bulgarian coconspirators spoke with him in English -- a language that none of the Bulgarian defendants admits to knowing. Martella wrote that Antonov first admitted to speaking "a little" English but then immediately retracted this admission.