Mehmet Ali Agca, the Turk convicted of having shot Pope John Paul II in 1981, testified today that he could not back up his claims that at least three Turkish accomplices were with him in St. Peter's Square when the pope was shot.

Agca's admission under interrogation by Judge Severino Santiapichi came in the sixth week of the trial of three Bulgarians and four other Turks who have been charged with having formed part of an elaborate plot to assassinate the pope.

The case is based almost exclusively on the often contradictory testimony of the 27-year-old Agca, who was arrested in St. Peter's Square immediately after the pope was shot and seriously wounded on May 13, 1981.

Agca, a right-wing terrorist, had escaped from prison in Turkey after being convicted there of the murder of an editor of a leftist newspaper.

He was tried in July 1981 and sentenced to life imprisonment. In that trial, he claimed that he had acted alone in shooting the pope.

Under continuing interrogation in an Italian jail after his conviction, Agca claimed he had only been a tool of Bulgarian secret services in an elaborate plot to kill the pope.

The trial of three Bulgarian and four Turkish defendants, which began May 27, stems from Agca's statements to Italian judicial investigators.

Having originally said that only one other Turk, fellow right-wing activist Oral Celik, 26, was with him at the scene of the shooting in St. Peter's Square, Agca has since implicated two others in court testimony: Omer Ay and Sedat Sirri Kaddem.

Both are free in Turkey and not included in the indictment that led to the current trial here.

Today's admission by Agca that the court had only his word about the presence of three other Turks at the scene of the assassination attempt came after public prosecutor Antonio Marini had shown him, once again, a series of three photos of the crowds in St. Peter's Square surrounding the pope's vehicle at the time of the shooting.

In the previous trial sessions, Agca had circled on a photograph three blurred heads in the crowd and identified them as his accomplices, even though there were no clear faces to be identified in the photos taken by journalists and tourists at the scene of the shooting.

Today, after Agca had pondered the photos for more than 30 minutes to confirm his previous identifications of his Turkish accomplices, Santiapichi asked whether Agca had some other proof -- either names of hotels, where the supposed accomplices might have stayed, or witnesses who had met them and could testify to their presence in Rome -- to establish the veracity of his claims.

"No, I can't give you any," said Agca.

Pressed again minutes later on the same issue by the judge, Agca repeated, "There isn't any, unfortunately."