Italian paramilitary police today arrested a second Soviet citizen in the spy case that surfaced last week with the arrest of a Soviet airlines official and an Italian microfilm company executive.

Viktor Konaiev, 38, deputy commercial director of an Italian-Soviet company called Nafta-Italia, was arrested at his home here under a warrant issued by Judge Domenico Sica, who had called him in for questioning two days ago.

The Italian news agency ANSA reported that the charge against Konaiev was complicity in political-military espionage with Genoese microfilm expert Azeglio Negrino and with Viktor Pronin, 46, deputy director of the Rome office of Aeroflot, the Soviet airline.

After Azeglio and Pronin were arrested last week, Italian press reports said Negrino was about to hand over microfilm of top-secret Italian weapons to his Soviet contact. Judicial sources have subsequently said that Negrino was cooperating with investigators but that Pronin, the first Soviet citizen to be charged here with espionage, has made no admissions.

A court today rejected a plea by Pronin's Italian lawyer for release of his client, ruling that grounds existed for his arrest.

Konaiev, like Pronin, has no diplomatic status. In the past decade, seven other Soviets have been implicated in espionage activities here but they all enjoyed diplomatic immunity and most were quietly expelled.

ANSA reported today that police had confiscated "important" documents from Konaiev's office, including copies of contracts between the Nafta comany and Negrino's microfilm company.

Following the arrests last week, judicial sources said Pronin and Negrino began their operations about a year ago. The microfilm firm reportedly had a high-level security clearance and had dealings with top Italian arms manufacturers. But officials of most of those firms have denied that the company had access to sensitive military data.