ROME (AP) _ Mehmet Ali Agca changed his story again Tuesday, subjected the court to a lengthy harangue and said there will be a ''major surprise'' soon in the trial of seven men accused of conspiring with him to shoot the pope.

Information Agca provided after his conviction, much of which he has contradicted, is the foundation of the case against three Bulgarians and four other Turks being tried for complicity in the shooting of Pope John Paul II on May 13, 1981.

Agca was repeatedly challenged Tuesday by a Turkish witness for the prosecution, Abdullah Catli, who procured the false passport Agca used to enter Italy. Catli was brought from France, where he is imprisoned on forgery and drug charges.

Returning to the trial after a day's absence, Agca disrupted it with a long outburst similar to previous ones. He alleged that U.S. and Italian officials, as well as Western secret services were withholding documents that could shed light on the attempt to kill John Paul.

''Nobody may want to believe me, but this is the truth. ... A major surprise will be revealed soon,'' said Agca, who often has given inconsistent testimony since the trial began in May.

The Turkish gunman, who is serving a life term for the attack that seriously wounded the pontiff, also is on trial for illegally importing the Browning pistol he used in the shooting.

Agca has said previously that he bought four Brownings in March 1981 from an arms dealer in Vienna, Austria. Catli insisted that he, Catli, bought two pistols from a Turk in Vienna and gave one to Agca.

Catli said a Turk who acted as his intermediary with the gun dealer could be summoned to verify his statement.

Agca, pushed by Prosecutor Antonio Marini to explain the conflicting testimony, changed his story about the guns.

''Well, I don't recall,'' he said. ''We were going to the place (to buy the pistols) but I stopped at a certain point. ... Oral Celik told me he bought the guns from an Austrian.''

Celik, also is charged with shooting the pope during a general audience in St. Peter's Square, still is at large. He is being tried in absentia, as are another Turk and two of the Bulgarians.

Catli has testified that Celik was watching television in Vienna when the shooting occurred.

Agca, who says Celik and two other Turks were with him in the square, also changed his story on how they planned to escape.

He told Italian magistrates earlier that they were supposed to get on a Vienna-bound truck from the Bulgarian Embassy in Rome. On Tuesday, he said that was the ''last resort,'' but did not describe other options.

Catli once led the Gray Wolves, a right-wing Turkish youth movement often accused of being involved in terrorism. Both Celik and Agca were active in it.