Italian judicial authorities ordered the release from prison today of two of seven Lebanese nationals accused of plotting to blow up the U.S. Embassy here.

The seven, originally all identified as members of the Lebanese terrorist group Islamic Jihad, were arrested here Nov. 24 after police discovered a detailed map of the embassy in one of the apartments they inhabited in the seaside resort of Ladispoli. At the time, Rome Police Chief Marcello Monarca said that there was "irrefutable proof" that the men "were preparing a massacre."

Today, however, Judge Rosario Priore, the examining magistrate in the case, ordered the release of Mohammed Nabil Merhi, 23, and Mohammed Ramsi Arzouni, 21. The judge, experienced in terrorism investigations, accepted the two men's claim to be only occasional acquaintances of the other five and to have spent only one night in the Ladispoli apartments, the court sources said.

The release spurred speculation in some political circles here, however, that the judge's decision might have come in response to mounting threats to the Italian Embassy in Beirut since the arrest.

The arrest of the seven prompted a series of anti-Italian threats by Islamic Jihad, which has demanded the men's release as well as that of two other suspected terrorists, Josephine Arkis Abdo, arrested in December in Rome, and Abdallah Mounzouri, arrested several months earlier in Trieste. The Italian Embassy in Beirut has increased security measures.

The release of the two Lebanese comes only a week after Swiss authorities rejected an Italian request for the extradition of Hussein Atat, an eighth suspect in the Rome bombing plot, and ordered him deported after suspending an 18-month jail sentence.

Atat was arrested in Zurich Nov. 18 for possession and transportation of explosives.

Asked about the release of the two suspects, a spokesman for the U.S. Embassy said only that Washington "has full confidence that Italian judicial authorities were acting in full conformity with Italian laws and judicial procedures."

Petitions for the release of all seven Lebanese on grounds that they are not members of Islamic Jihad and that there is insufficient evidence that they were planning an attack have been turned down by the judge.

No trial date has been set, but court sources say that Priore is continuing his investigation and that the map discovered by police, who had the group under surveillance for some time, is a major piece of evidence.