Three Bulgarians, a second Italian trade unionist and an unnamed Italian state employe have received judicial warnings that they are under investigation in connection with an alleged plot to kill Polish Solidarity leader Lech Walesa when he visited here in January 1981, the Italian state news agency reported today.

Rome magistrates issued the warnings to Salvatore Scordo, an official of the UIL trade union and a consultant to a Social Democratic Cabinet minister, to an unnamed employe of the Italian national energy corporation, ENI, and to three former staff members of the Bulgarian Embassy in Rome, Todor Ayvazov, Zelio Kolev Vassiliev, and Ivan Dontchev.

Scordo was picked up for questioning today, and his home and office were searched by police. Ayvazov and Vassiliev were implicated in the judicial probe into the May 1981 attack on Pope John Paul II.

Dontchev, who reportedly left Italy more than a year ago, was mentioned by Justice Minister Clelio Darida during a December parliamentary debate as a suspected contact for trade unionist Luigi Scricciolo, arrested a year ago on charges of terrorism and political-military espionage.

Judicial sources say Dontchev was believed to be, with Ayvazov, one of two Bulgarians who sought, through Scricciolo, to make contact with the Red Brigades while members of the group were holding kidnaped U.S. Gen. James Dozier.

The new judicial warnings, which are not formal indictments but legal measures to permit interrogation, bring to eight the number of people warned in connection with the alleged plan to kill Walesa.

On Monday, the magistrates issued similar warnings to Serghei Ivanov Antonov, the Bulgarian jailed on charges of involvement in the attempt on the pope, to Mehmet Ali Agca, the Turkish gunman now serving a life sentence for shooting the pope, and to Scricciolo.

According to Italian state television's evening broadcast, Scricciolo told the magistrates about the contacts between Dontchev and Scordo, whose financial situation was being investigated.

The Bulgarians and Scordo could plead, however, that it was normal for them to deal with each other; union correspondence documents a conventional working relationship.