Bulgarian citizens have been heavily implicated here in arms, drug and cigarette smuggling, according to several judicial and police investigators. High-level officials suggest that the East Bloc state may use the proceeds from smuggling to finance spying or terrorist activities.

Bulgarian officials already have been accused of having a role in the May 1981 attempt to kill the pope, and judicial investigators are studying a possible Bulgarian attempt at involvement in the Red Brigades' kidnaping of U.S. Brig. Gen. James L. Dozier in late 1981. Several Bulgarians also are under investigation for possible involvement in an alleged plot to kill Polish union leader Lech Walesa. All of the charges have been strongly denied by Bulgaria.

The sum of the information obtained in the various investigations of the Bulgarian government's role in alleged criminal activities suggests at least that Bulgaria has had little regard for Italian laws in its desire to earn hard currency, in the view of observers here.

More seriously, some observers see a pattern of behavior suggesting that Bulgaria may have replaced Czechoslovakia as the East Bloc country most eager to support terrorist activities here as a means of destabilizing this faithful NATO country. In this view, Bulgaria is serving as the Kremlin's henchman by planning assassinations or other covert operations.

There have been no new major developments in the probe into the attempt to kill Pope John Paul II since the arrest last November of a Bulgarian airlines official on charges of active complicity in the case and the later implication of two former Bulgarian Embassy officials in the attack. But the activities of the magistrates involved in the papal probe and the other investigations involving Bulgaria suggest that the various cases may be related.

Rome magistrates Ferdinando Imposimato and Domenico Sica, who are assigned to the case related to the Dozier kidnaping, and Judge Carlo Palermo, who heads an investigation into a major arms and drug smuggling ring, have interrogated convicted papal assailant Mehmet Ali Agca in prison. The three Bulgarian officials were implicated in the papal shooting primarily by Agca's testimony, officials say.

Palermo returned Thursday from an 11-day visit to Sofia, where he interrogated Bekir Celenk, a Turkish businessman who has been implicated both in smuggling and in the papal attack. He reportedly arranged to offer Agca 3 million West German marks to kill John Paul.

Palermo, a magistrate in Trento, is responsible for the investigation of a giant arms and narcotics ring. According to his probe, major decisions by a gang of Italians, Turks and Middle Easterners were made at regular meetings in Bulgaria.

The court documents in that case state that Bulgaria is a narcotics producer as well as a key country of transit for the smuggling. They also say that shipments of arms have been rerouted from Bulgaria to insurrectionist groups in various countries.

A recent report by the customs police on cigarette smuggling cites Bulgaria--followed by Romania--as the principal culprit among East Bloc countries in tobacco smuggling that has been going on for at least a decade.

Late last year the customs police filed a suit in Trieste against the officials of a Bulgarian state trading company, Despred, for its alleged involvement in what was termed a "continuous influx" of smuggled cigarettes from the Bulgarian ports of Burgas and Varna and from the Pioner and Sofia train stations.

Socialist Finance Minister Francesco Forte, who last month sent an official note of protest to the Italian Foreign Ministry over the issue, said that the evidence accumulated so far reveals "a direct responsibility" on the part of the Bulgarian government that he described as "intolerable."

"Given the tight control of the Bulgarian government over the country's state enterprises, it is clear that the government itself must be involved," Forte told The Washington Post.

Another inquiry, involving alleged espionage and terrorist activities by a jailed Italian trade unionist, Luigi Scricciolo, is continuing into Scricciolo's reported contacts with Bulgarian officials.

The Italian press has reported that one of the accusations against Scricciolo, former head of the international relations department of the center-left Union of Italian Labor, was that he sought to arrange a meeting between Red Brigades terrorists holding kidnaped Gen. Dozier and one or more Bulgarian Embassy officials.

A Red Brigades terrorist captured during the rescue of Dozier by Italian police in January 1982, Antonio Savasta, subsequently testified that Scricciolo had taken part in attempts by the Bulgarians to become involved in the kidnaping.

According to sources close to investigating magistrate Imposimato, the case is believed to be significant because it could indicate to what degree East Bloc secret services were involved in Italian or West European terrorism.

The magistrate's theory reportedly is that the Bulgarians knew that Scricciolo's cousin, Loris, was a Red Brigades member and asked the unionist to arrange through him a meeting with a brigades' member. According to press reports the meeting was to be in front of the Holiday movie house in Rome, but, for unknown reasons, it never took place.

A spokesman for the Bulgarian Embassy has said that having relations with Scricciolo was normal because of the latter's job in coordinating his union's international activities. Since then, however, it has been revealed that Scricciolo's contacts with the Bulgarians dated back to the time that they had helped to finance a small, leftist group to which he belonged.

In a speech to the Italian parliament last December, Socialist Defense Minister Lelio Lagorio said that intelligence agencies here had picked up abnormal and intense radio traffic between Bulgaria and Rome during the U.S. officer's kidnaping that were similar in intensity only to transmissions picked up at the time of the papal shooting in May 1981.

In the early 1970s, Italian investigators turned up evidence that left-wing terrorists here had been able to use Czechoslovakia as a refuge in times of need. And although hard evidence has never been produced, there also were recurring rumors of terrorist training camps in that country. The more recent testimony by captured terrorists like Savasta has suggested that after Czechoslovakia became notorious, Bulgaria could have picked up a support role.

A published report by the customs police command dated last Dec. 17 deals with frequent truckloads of equipment covered by diplomatic privilege arriving in Italy from Bulgaria. It said both the Italian secret service and the Foreign Ministry had been notified of suspicions regarding the content of the shipments, which could contain contraband.

This information had also been passed on to the "Rome magistrate conducting the investigation on activities of Bulgarian citizens in Italy," the document notes.

Until Bulgaria agreed to allow Palermo to visit Sofia to interrogate Celenk, the Bulgarian government had not cooperated with the Italian investigation, according to Italian authorities.

Documents from the arms and narcotics investigation state that while countries like Yugoslavia and Greece had been helpful, others, "in particular, Bulgaria, did not offer any assistance, failing even to respond to the very serious requests for verification forwarded by our central offices." The customs police document on cigarette smuggling also complains that all attempts to get cooperation from the Bulgarians had failed.

Because cigarette sales are taxed heavily in Italy, which limits imports of foreign cigarettes to protect its own national tobacco production, cigarette smuggling has long been a problem for Italian tax officials.

But over the decades the pattern of that smuggling has shifted and, according to a customs police spokesman, at least a third of the foreign-trademark cigarettes smuggled into Italy now come from Eastern European countries, mostly Bulgaria and Romania but also including East Germany, Albania and Yugoslavia.

The spokesman said that in 1982 alone, customs police in Trieste had uncovered traces of shipments of cigarettes from the East Bloc totaling 603 tons. The suit filed late last year in Trieste followed the discovery of a shipment of 102 tons from the Despred company in Bulgaria.