Italian police backed by helicopters arrested almost 100 suspected mobsters Tuesday and thwarted a plan by the hobbled Sicilian Mafia to reconstitute itself and form a new ruling commission to set strategy, authorities said. Carabinieri police in Palermo said the operation there and in other Sicilian cities was one of the largest in recent years and gave investigators a picture of the new highest echelons of the Mafia. It also prevented possible bloodshed as bosses vied to control the commission. The raids involved 1,200 police officers and helicopters. They targeted the bosses of local families and lower-level mobsters intent on setting up the commission, which was to make Cosa Nostra's important decisions such as possible attacks, police said.