An Italian microfilm expert arrested yesterday along with a Soviet airline official had in his possession hundreds of documents and microfilms showing Italian and NATO military secrets, Italian news media reported here today.

The Italian news agency ANSA said Azeglio Negrino, 45, an executive of a Genoa microfilm company, had been planning to turn over to Viktor Pronin, 46, deputy chief of Aeroflot's Rome office, "several hundred microfilms" depicting secret military documents, weapon designs and models and military installations when he was picked up yesterday by national police and defense intelligence officers at an undisclosed location in central Rome.

In an earlier news report, the Italian state television, RAI, said that Negrino, a top officer of the Microlito firm, had the plans for a new NATO air weapon and was planning to turn them over to his Soviet contact.

The Milan newspaper Corriere della Sera reported that the microfilm included pictures of NATO military installations in the Friuli and Veneto regions of Italy.

A spokesman for the Carabinieri, the Italian police force that is part of the armed forces, said yesterday that Negrino's arrest came after he was caught in the act of passing military secrets. The spokesman gave no details of the content of the microfilm Negrino sought to turn over to Pronin but said the material involved was "of prime strategic importance." He said the arrest of Negrino and the jailing of Pronin for questioning was the climax of a one-year operation by Carabinieri and officials of Sismi, the defense intelligence agency.

The two men are now being held in isolation in a Rome prison and are to be questioned Wednesday by prosecutor Domenico Sica who must decide whether or not to file formal charges against Pronin. Ansa also reported today that while a great deal of incriminating material had been found in Negrino's Rome hotel room, and more in his Genoa home, a search of Pronin's Rome home had turned up no hard evidence.