The trial of the alleged conspirators against the life of Pope John Paul II resumed after a summer recess here today with a Turkish witness asserting that the Bulgarian secret services had prior knowledge of the plot.

The new allegations of a "Bulgarian connection" to the plot to kill the Polish-born pope were made by Yalcin Ozbey, a longtime friend of papal assailant Mehmet Ali Agca. It marked the first time that the court had heard testimony on Bulgarian involvement in the conspiracy from any witness other than Agca himself.

Although Ozbey supported some of Agca's accusations against the Bulgarian secret services, his account differed on several key points and appeared to be based entirely on hearsay. Ozbey's credibility as a witness has been challenged by the defense because of repeated contradictions, errors, and retractions of pretrial statements that he made to Italian magistrates who interviewed him in a West German prison cell.

The resumption of the trial after a seven-week summer break was marked by yet another outburst from Agca who has claimed in the past to be Jesus Christ. After being granted permission to make a statement, he accused both the White House and the Vatican of plotting to exploit his allegations of Bulgarian involvement to launch a propaganda campaign against the Soviet Bloc.

It was largely due to Agca's testimony during a three-year investigation into the papal assassination attempt that three Bulgarians and four Turks are now on trial in Rome.

"The Vatican and the White House, together with their accomplices in the western secret services, want to dominate the world with lies and calumny. All will fail miserably because the truth is invincible," Agca proclaimed, raising his voice to a shout.

Today's testimony underlined the difficulties faced by the Italian court in evaluating the statements of either man. Agca and Ozbey, who were members of the same right-wing Turkish terrorist group, both have displayed a capacity for making sweeping accusations while providing scarcely any hard evidence that can be corroborated independently.

In his testimony, Ozbey said that Agca and two other Turks told him that they had outlined their plans to murder the pope to the Bulgarian authorities. He said that the Bulgarians showed some initial interest in the project but did not play any direct role because they mistrusted Agca.

According to Agca's account, the assassination attempt was directly supervised by three former Bulgarian officials in Rome. The former deputy Rome station manager of the Bulgarian state airline Balkanair, Sergei I. Antonov, has been in detention in Italy for nearly three years on Agca's charges.

Under cross-examination, Ozbey said he had no direct knowledge of the papal assassination attempt. He said he had learned details about the plot from Agca himself and two Turks whom the papal assailant had named as his fellow-conspirators: Oral Celik and Sedat Sirri Kadem.

Kadem, a former left-wing terrorist who now lives in Turkey, denied any part in the papal plot when he was brought to Rome in August for a special court session. He insisted that he had never traveled outside Turkey in his life.

Ozbey's initial description of Kadem, provided to Italian magistrates during the pretrial investigation, was wildly inaccurate. He described the leftist as blond and fairly tall when in fact he is dark and relatively short.

Seeking to explain his earlier testimony, Ozbey today said that he had been trying to "protect" Kadem. He did not elaborate.

Ozbey, who faces charges in West Germany for fraud and drug smuggling, repeatedly tried to extract guarantees of immunity from prosecution, but his pleas were brushed aside by the presiding judge, Severino Santiapichi.