Italian magistrates have confiscated records of the Bulgarian national airline office here on suspicion that it was a cover for intelligence activities, judicial sources said today. The action came as a high-ranking police source confirmed newspaper reports that the gunman who shot Pope John Paul II told interrogators that Bulgarian agents, including the head of the airline office, helped plan the attack.

In a separate development, the Bulgarian news agency reported that police in Bulgaria have detained Bekir Celenk, a Turk, charged by Italian magistrates with complicity in the May 1981 shooting of the pope.

Celenk, an alleged smuggler, is said to have arranged meetings between Bulgarian officials and Turkish gunman Mehmet Ali Agca, and to have offered Agca 3 million West German marks (about $1.25 million) to kill the pope.

The Bulgarian agency also sharply denied that Bulgaria was involved in any plot against the pontiff's life. Bulgaria, one of the Soviet Union's most loyal allies, is suspected of having plotted to kill John Paul because of the Kremlin's irritation with his support for the independent trade union Solidarity in his native Poland.

The head of the Balkan Air office in Rome, Sergei Ivanov Antonov, was arrested Nov. 25 on suspicion of "active complicity" in the shooting in St. Peter's Square.

Examining magistrate Ferdinando Imposimato ordered confiscation of the airline office's books after an Italian trade unionist jailed on spying and terrorism charges confessed to having had active contacts with several Bulgarian officials, according to reports in all of Italy's leading newspapers.

The reported confession of left-wing unionist Luigi Scricciolo provided no new details about the attempted assassination of the pope but focused new attention on Bulgarian activities here.

Scricciolo is facing charges of espionage, terrorism and complicity in the kidnaping last year of U.S. Brig. Gen. James L. Dozier by the Red Brigades urban guerrilla group. Two Red Brigades members have testified that the Bulgarians sought to provide help in that kidnaping.

The senior police source said that reports appearing yesterday in several Italian newspapers, which described how Antonov and Bulgarian Embassy cashier Teodorov Ayvazov allegedly participated in planning the attack on the pope, "appeared to be more or less correct."

But the press accounts, clearly leaked by a single unidentified source, caused considerable skepticism in political and journalistic circles. The report that a Bulgarian official had trudged to St. Peter's Square with a hand grenade in his attache case aroused amazement.

The newspaper reports said the description of the Bulgarian agents' roles had been provided by Agca, the Turk now serving a life sentence in an Italian jail for wounding the pope and two American tourists standing nearby in the square.

The arrest of Celink in Bulgaria could be an attempt to show that the East European nation was cooperating with Italy in the investigation. It also appeared possible, however, that Bulgaria hoped to gain leverage with Rome in seeking the return to Bulgaria of Antonov. The Bulgarian news agency reaffirmed its government's position that the airline office chief was innocent and should be released.

The arrest of Antonov and charges that two other Bulgarians were involved in the assassination attempt already have drawn sharp diplomatic criticism from Bulgaria.

An Italian Foreign Ministry official confirmed that the ministry had asked the Bulgarian government to revoke the diplomatic privileges of Ayvazov, currently "on holiday" in Bulgaria. The official said that the Bulgarian government had refused, however, saying that evidence of his guilt was not sufficient.

The Italian official added that no further diplomatic action against Bulgaria had yet been considered, despite the country's implication in the assassination attempt, the spying case, and a drugs-for-arms investigation in northern Italy. The ministry had not yet received official communication from the Italian magistrate's office regarding most of the facts in the latest press reports, he said.

The confiscation of the Balkan airline office's books came after the arrested Italian unionist Scricciolo admitted that he regularly used Balkan Air Lines flights whenever he traveled abroad in his job as a trade union representative, judicial sources said.

According to press reports today, Scricciolo after several months in jail now has named four Bulgarian officials with whom he had contacts.