Antiterrorist police in Rome today arrested a Bulgarian Airlines official on charges of active complicity in the May 1981 attempted assassination of Pope John Paul II.

Acting on a warrant issued by Judge Ilario Martella, the chief Italian investigator in the case, officers of the Digos investigative police branch this morning picked up Sergei Ivanov Antonov, 35, at the Balkan Tourist Office, the Bulgarian airline's travel agency in downtown Rome.

After the arrest, the Bulgarian Embassy issued a statement saying Antonov was "honest and innocent" and that his arrest could damage Bulgaria's relations with Italy and the Vatican.

The arrest was the fourth since the pontiff was shot and seriously wounded in St. Peter's Square on May 13, 1981, by Turkish gunman Mehmet Ali Agca, and it was the first involving an Eastern European.

As such, it is expected to refuel speculation about the possible involvement of Soviet Bloc intelligence agencies raised by recent U.S. media reports.

Police today were closemouthed about the details of the charges against Antonov, a tall man with short, dark curly hair, glasses and a moustache who appeared calm as he was led handcuffed into Rome's downtown police headquarters.

But Justice and Interior Ministry sources said that Antonov, who lives alone in a two-room apartment near his office, was suspected of providing Agca with a possible hide-out.

Martella has never made explicit references to the possibility of Eastern Bloc involvement, saying that he would do so only if he had positive proof. He also has said he couldn't exclude that possibility.

His investigation, however, has been based on the assumption that Agca did not act alone.

Earlier this month, Martella told reporters from several Italian newspapers that his 17-month-old inquiry was approaching a turning point. In October, Omer Bagci, a right-wing Turk arrested in Switzerland in June on charges of supplying Agca with a gun, was extradited to Italy.

And on Nov. 3, West German police in Frankfurt acted on information relayed by Martella to arrest Musa Cedar Celebi, another right-wing Turk who headed a Turkish cultural organization.

Last week Martella flew to Frankfurt to interrogate Celebi, and it is believed that Antonov's arrest may have stemmed from information the Italian judge received at that time.

There also was unconfirmed speculation that Antonov might have been in or near St. Peter's Square at the time of the assassination attempt. Martella was unavailable for comment, but in an interview several weeks ago he said there was then no proof that Acga, who was apprehended after the attempt and is now serving a life sentence, had accomplices in the square.

The interest regarding the arrest of a Bulgarian stems from Agca's testimony that he spent time in Bulgaria after escaping from prison in 1970.