Mehmet Ali Agca, the Turkish would-be assassin of Pope John Paul II, today insisted that he never had killed anyone despite earlier confessing to the murder of a prominent Turkish newspaper editor.

Called to give evidence in the trial of three Bulgarians and four Turks accused of acting as his accomplices in a plot to kill the Polish-born pope, Agca spoke in halting but concise Italian. His measured behavior contrasted sharply with emotional outbursts last week in which he claimed to be "Jesus Christ" and predicted the end of the world.

Agca's return to the witness stand came after almost a week of testimony by another of the accused Turks, Omer Bagci, that has raised the court's suspicions that other Turks could have been involved.

Bagci frequently contradicted himself and was unable to explain fully his contacts with other right-wing Turks.

In pretrial testimony, Agca had said that he tried to kill the pope on instructions from the Bulgarian secret service at a time when the Kremlin was attempting to restore its control over the Soviet Bloc. Agca has not yet been questioned directly in open court about his allegations against the Bulgarians.

Asked to describe how he became a terrorist, he said that he had become interested in right-wing ideology as a youngster in eastern Turkey.

He then made contacts with the Gray Wolves, a right-wing Turkish terrorist group, in the Turkish capital of Ankara, where he attended university in 1977.

Asked if he shared the philosophy of the Gray Wolves, a group regarded in Turkey as the military wing of the ultra right-wing Turkish Nationalist Party, Agca replied, "very little," adding that the Gray Wolves did not have any constructive solution to Turkey's problems.

Depicting himself as an "ideologue" and organizer of terrorist acts, Agca said that he had used groups such as the Gray Wolves for his own purposes but was never used himself.

"It has always been my principle to avoid hurting innocent people . . . I never killed anyone," he said.

When Judge Severino Santiapichi pointed out that he had confessed to the 1979 murder of Abdi Ipekci, a liberal Turkish journalist, Agca replied that he had done so only in order to protect "about 60 people" who were involved in the affair. He said that a "hidden power, . . . powers connected to the state" had been behind the Ipekci assassination, but he refused to go into details.

Dressed, as usual, in a light blue suit and an open-necked blue shirt, Agca seemed relaxed as he sat cross-legged in front of the judge. He insisted in speaking in the Italian that he has learned in prison since May 1981, when he fired two shots at John Paul II in St. Peter's Square.

Agca was shown a picture of a Turk, Samet Aslan, arrested in the Netherlands last month during a papal tour but insisted that he did not recognize him.

The suspicions of Dutch police were aroused when Aslan was found to have a pistol of the same make as the semi-automatic Browning used by Agca to shoot the pope.

Earlier, the court completed its interrogation of Bagci, a Turkish worker in Switzerland who is accused of smuggling Agca's pistol into Italy.

Bagci insisted that he first met Agca in early 1981, but Judge Santiapichi has raised the possibility that the two men could have met at least six months earlier in Bulgaria.

Stamps in Bagci's passport appear to show that he entered Bulgaria on Aug. 30 or 31, 1980, and crossed into Turkey on Sept. 1. This coincides with a trip made by Agca in the opposite direction from Bulgaria to Western Europe with a forged passport in the name of Faruk Ozgun.

Pressed repeatedly by the judges to admit that he had met Agca in Bulgaria, Bagci said that he had merely spent a few hours in the country on his way to Turkey for a vacation.

Since the passport stamps are somewhat unclear, the court is insisting on further forensic tests and police investigations to try to establish exactly when Bagci was in the Communist state.

Bagci, who has sought to minimize his own role in the plot, acknowledged that he was accompanied on his trip by other Turks with links to the Gray Wolves, including a known friend of Agca's by the name of Erdem Eyup.

Another apparent coincidence uncovered by the judges occurred in the Swiss city of Zurich, just six weeks before the assassination attempt in St. Peter's Square.

In pretrial testimony, Agca described a strategy session that allegedly took place in Zurich at the end of March 1981 involving himself and two of his fellow accused: Musa Serdar Celebi, the leader of a right-wing Turkish group in West Germany, and Bekir Celenk, a Turkish businessman with ties to Bulgarian authorities. Italian police have linked Celenk to arms and drug smuggling activities.

Under cross-examination by the judges, Bagci admitted that he also had been in Zurich at the end of May 1981 and had seen Celebi. He made no mention, however, of either Celenk or Agca.

The public prosecutor has taken the first step toward opening a new investigation of right-wing Turks who associated with Agca.

Half a dozen names of possible suspects emerged from Bagci's testimony including several Turks who are likely to be called as witnesses later in the present trial.