An Italian court wound up an exhaustive international inquiry today into the attempted assassination of Pope John Paul II in May 1981.

As the trial of three Bulgarians and five Turks accused of plotting to kill the Polish-born pontiff nears its end, Italian judges this week visited the city where the alleged Soviet Bloc conspiracy is supposed to have originated in the summer of 1980.

But they were unable to shake blanket denials by the Bulgarian defendants that they ever had any dealings with papal assailant Mehmet Ali Agca.

The session in Bulgaria concludes the hearing of testimony by the Italian court, which already has traveled to West Germany, Turkey, Switzerland and the Netherlands in its attempts to piece together the background of the assassination attempt. Defense and prosecution counsel will make their concluding speeches in mid-January, and the final verdict is expected in early February.

Under Italian law, there are three possible verdicts: guilty, innocent or acquittal of the defendants for lack of proof.

According to the Italian indictment, Agca was paid the equivalent of $1.8 million to shoot John Paul II on behalf of the Bulgarian secret services at a time when the Soviet Union was worried about social and political upheavals in the pope's native Poland. Plans for the assassination attempt were alleged to have been made at a series of meetings between Agca and his alleged Bulgarian accomplices in Sofia and Rome.

Despite more than 100 court sessions, and the interrogation of more than 50 witnesses, the court has been unable to find any trace of the money alleged to have been paid to the Turkish gunman for shooting the pope.

Nor has there been any independent corroboration of the numerous meetings that Agca said took place between him and the Bulgarian defendants.

The trial, which began on May 27, also has failed to turn up convincing evidence to support charges by defense lawyers and the Bulgarian government that Agca was manipulated by the Italian secret services while in detention at the top security prison Ascoli Piceno.

The counterconspiracy theory appeared to gather momentum last summer when a former inmate of the prison, Giovanni Pandico, gave a magazine interview in which he described meetings between Agca and the former deputy head of the Italian secret service, Gen. Pietro Musumeci. But Pandico, a former gangster with Mafia connections, proved a contradictory and unreliable witness when he appeared before the court earlier this month.

An Italian magistrate charged with leading an investigation into Pandico's allegations has since closed the case for lack of evidence.

Originally dubbed "the trial of the century" by the Italian mass media, the court case seems likely to disappoint both western proponents of a "Bulgarian connection" to the assassination attempt and communist propagandists who accused the CIA of launching a smear campaign against the Soviet Bloc. Much of the past seven months have been taken up by the laborious examination of contradictory testimony by witnesses who proved to be unreliable, beginning with Agca, who startled the court on the first day with a claim to be Jesus Christ.

In private, a senior Bulgarian official who has followed the case closely said he expected the trial to end with the intermediate verdict of lack of proof for the Bulgarian defendants, which will still leave an element of doubt about their guilt or innocence. This is also the view of many Italian journalists who have covered the case in Rome.

Today's session was devoted to a cross-examination of the two former Bulgarian officials in Rome, Lt. Col. Zhelyo Vasilev and Todor Aivazov, accused by Agca of acting as his control officers in the Bulgarian capital. Bulgaria has refused Italian requests for the extradition of the two men, who left Italy in 1982 before they could be arrested.

An elaborate alibi presented by Aivazov for the days leading up to the assassination attempt was challenged by the Italian judges, who cited contradictory testimony by other witnesses. Aivazov, the former cashier at the Bulgarian Embassy in Rome, pleaded that it was difficult to remember his precise movements 4 1/2 years later.

The one concrete result of the trial so far has been the opening of a new investigation into Agca's Turkish acquaintances. This opens up the prospect of a new round of legal proceedings with a new set of defendants after the current trial.