A Bulgarian colonel accused by Italian magistrates of masterminding a communist plot to assassinate Pope John Paul II finally got his day in court today -- and denied any connection with papal assailant Mehmet Ali Agca.

The proceedings were supervised by a Bulgarian judge with dozens of Bulgarian journalists in attendance and state television cameras whirring.

On a platform on one side of the courtroom, a converted conference hall at a downtown Sofia hotel, were the Italian judges who have presided over the eight-month-old trial in Rome of the alleged Bulgarian and Turkish conspirators. On the other side sat Bulgaria's state-sponsored committee for the defense of Sergei I. Antonov, the only Bulgarian defendant in Italian custody.

Taking the witness stand was Lt. Colonel Zhelyo Vasilev, who was assistant military attache at the Bulgarian Embassy in Rome between November 1979 and August 1982. Vasilev has been depicted by Agca as the brains behind the assassination attempt as well as other alleged plots to kill Tunisian leader Habib Bourguiba, former Maltese Prime Minister Dom Mintoff and Polish Solidarity union leader Lech Walesa.

It was in Sofia, at another hotel across town, the Vitosha, that the plot to shoot the pope was allegedly hatched in the summer of 1980. According to the Italian indictment, which was based largely on Agca's own testimony, the Bulgarian Secret Service wanted to murder the Polish-born pope to help suppress the labor upheaval in Poland.

It has been established that Agca spent up to eight weeks in Sofia between July and August 1980 after his escape from Turkey where he was wanted for the murder of a prominent newspaper editor.

Since the papal trial began last May, Agca's credibility has been undermined by contradictory statements and claims to be Jesus Christ. The court, however, has still not resolved how he was able to provide Italian magistrates with a number of personal details about the Bulgarian defendants, including Vasilev, who claim they never met the pope's would-be assassin.

The details include knowledge of the movements of the Bulgarian defendants, their personal characteristics and the telephone numbers of the Bulgarian Embassy in Rome. Agca also described a getaway plan involving a diplomatically sealed truck that left the embassy on the day of the assassination attempt, May 13, 1981.

Vasilev scorned Agca's claims to have had extensive dealings with him when Agca could not accurately state Vasilev's height in pretrial testimony.

The questions and answers were translated simultaneously into five languages: Bulgarian, Italian, English, Russian and French. Tight security was in force with Bulgarian police and secret service men armed with two-way radios patrolling the Moskva Park Hotel.

Accused by Agca of taking part in several reconnaissance missions to St. Peter's Square on the day preceding the assassination attempt, Vasilev today told the court that he had spent most of the period in question at the Bulgarian Embassy. He said he was responsible for maintaining communications with Sofia on behalf of the military attache, and provided a detailed schedule of the broadcast to support his alibi.

The alibi is unlikely to be accepted by the Italian court on the grounds that it can only be corroborated by other Bulgarian officials, who themselves constitute an interested party.

Vasilev denied any knowledge of English -- the language in which the Bulgarian defendants are alleged to have communicated with Agca. The Italian court has produced no conclusive evidence that any of the Bulgarians can use more than a few words of English.

Agca has claimed that he got in touch with Vasilev by phoning him at the embassy and asking for "Sotir Petrov," the Bulgarian attache's alleged code name. He did not know his real name.

Vasilev today described this method of communication as ludicrous since it assumes that the embassy switchboard operator also knew his secret code name. He noted that Agca had not known about a direct line to the attache's office.

"If I really was such a crazy terrorist, would I not have given Agca this private telephone number? Why would I have given him numbers that dozens of people use?" he asked.