The chief Italian investigator of the attempted murder of Pope John Paul II said today that he has assembled a mass of evidence suggesting a link between the would-be papal assassin and former Bulgarian officials in Rome but would leave the task of speculating about a motive for the conspiracy to politicians and journalists.

Outlining the contents of a 1,243-page indictment that he filed in court last week, Judge Ilario Martella said that he had devoted 123 pages to examining allegations of a "Bulgarian connection" to the plot. He said that chapter, the longest in the report, dealt with the position of the three Bulgarian defendants and the controversial stay of papal assassin Mehmet Ali Agca in Bulgaria in the summer of 1980.

The judge, who spent the last three years investigating the attempt on the pope's life in St. Peter's Square in Rome on May 13, 1981, has been reluctant to comment on the results of his inquiry prior to the release of the detailed indictment. He agreed to discuss the case informally on the understanding that his remarks would not be quoted directly.

Since handing down the indictments, Martella has received more than 50 requests for formal interviews from world media organizations, all of which he has so far refused. He explained his reluctance to talk in public by depicting the papal plot as a highly complex case that could be easily misunderstood by singling out individual episodes rather than viewing the mosaic of details as a whole.

Only 13 pages of the report -- containing formal charges against five Turks and three Bulgarians -- have been made public. Martella said that the entire document, which will provide the basis for the criminal trial, will be handed over to the Rome Court of Assizes on Wednesday and will later become available to defense lawyers.

The report, which is drawn from 25,000 pages of still secret evidence, contains details that can be used by both the prosecution and defense in arguing their case. Martella said he had devoted four chapters to examining the behavior of Agca under interrogation, including the possibility that some of his testimony about the Bulgarian accused could have been derived from the press or television.

Stressing that he had attempted to bring out all sides of the case in his report, Martella rejected criticism in the official Bulgarian news media of his decision to indict two former Bulgarian diplomats in Rome and the deputy head of the Bulgarian airline Balkanair. The indictments were described as "shameful" and "unfounded" in an official Bulgarian statement.

The judge's obvious irritation at the Bulgarian attacks appears to stem at least in part from the fact that he went out of his way to give credit to the Bulgarian authorities for cooperating in his inquiry. He told a press conference last week that information supplied by both Turkey and Bulgaria could have an impact on the result of the case.

Asked about the motive behind the conspiracy, Martella said that his formal indictment stated that Agca had acted with the encouragement and support of three Bulgarian officials then in Rome. He added, however, that he had not attempted to draw links between the plot and the social and political upheavals in the pope's native Poland in 1980-81.

A report filed in court by the public prosecutor, Antonio Albano, said that a senior Soviet Bloc politician had ordered the killing of the pope to remove the religious inspiration for the now outlawed Solidarity trade union. Albano also depicted the Bulgarian secret services as controlled by the Soviet secret police, the KGB.

Martella said that anybody was free to put a political interpretation to the facts that he had gathered but this had not been part of his task. It was up to politicians and journalists to make such deductions, he added.

The conversation took place in Martella's modest office on the fifth floor of the concrete-and-glass building on the outskirts of Rome that houses the Italian judiciary. Midway through, prosecutor Albano arrived to append a legal note to the only extant copy of the mammoth indictment, which Martella has kept under close guard since he completed writing it earlier this month.

Both magistrates, who have worked together closely, were smiling and relaxed after the completion of the marathon inquiry. Under Italian judicial procedures, their role is limited to the preparation of the trial and has now ended.

Among the questions examined closely by Martella in the indictment are the alibis of two of the Bulgarian accused, Sergei I. Antonov and Todor S. Aivazov, who Agca claimed were with him in St. Peter's Square on the day of the assassination. Martella has depicted the alibis as inconsistent.

Martella said that in his indictment he had paid particular attention to the position of Bekir Celenk, a Turkish businessman accused by Agca of promising 3 million West German marks ($1.2 million) for the assassination on behalf of the Bulgarian secret service. The judge said there was evidence that Celenk and Agca had communicated by phone but refused to give details.

Celenk is at present in Bulgaria where he is under police supervision and is prevented from leaving the country. Like the Bulgarian defendants, he has denied ever meeting Agca. Martella said there was also evidence of ties between Celenk and Musa Serdar Celebi, the leader in West Germany of a Turkish right-wing emigre organization that allegedly gave logistical support to Agca. Celenk has acknowledged one meeting with Celebi, some years ago.

The judge said he had closed an investigation into allegations by Agca of a plot to kill Solidarity leader Lech Walesa on the grounds that it could not be proven whether such a plot had in fact existed. Agca has withdrawn part of his testimony about carrying arms and explosives to the scene of the would-be assassination.

Martella said the fact that he had ordered the case to be dropped obviously meant that there was not enough evidence at this point to justify a trial. Under Italian law, a case that has been closed can be reopened only in the event of new evidence.