Terrorist shootings and bombings erupted in six Italian cities Wednesday night and early yesterday, leaving one man dead and two injured.

A night watchman, Remo Pietroni, 39, was found dead on the outskirts of Florence, near a car containing explosives. Police said they think Pietroni surprised a group of guerrillas preparing to bomb a nearby power station and said they have arrested seven persons in connection with the killing.

The Red Brigades, Italy's most publicized leftist guerrilla organization, claimed responsibility for the shootings in Turin and Milan of two Fiat car company executives, one of whom was seriously wounded. The other became the seventh person to be shot in the legs in the last 12 days.

The shootings came after bombings during the night in Bologna, Pordenone, Rome and Spoleto, where a bomb damaged the wall of the local prison. Police blamed both rightist and leftist groups for this most recent wave of terrorism.

A new terrorist group, calling itself the Organized Proletarian Youth," appeared on the political scene for the first time, claiming responsibility for several of the bombings.

The night of violence followed an agreement by Italy's six major political parties - including the Communists - to join in cracking down on political terrorism.