The word "comedy" strains at the prospect of a film set during one of the less humorous months in Italian history-September 1943, when the Badoglio government signs an armistice with the Allies while Mussolini busily sets himself up as a German puppet. You wouldn't have to be Alberto Sordi to be addled at this confluence of events-but for the sake of comedy, it helps. He is a second lieutenant, Alberto Innocenzi, who would do his duty if he could figure out what it was; in the meantime, like most of his comrades, he prefers to accept the Badoglio invitation to lay down arms and go home. This he attempts amid a seesaw of humor and horror which the film recreates with dizzying alternations. When he finds in place of home a father who has allied himself with the Fascists, Innocenzi sets out again, this time hoping to salvage a measure of human dignity in the fray. Director Luigi Comencini, by 1960, has himself left the innocenza of the Bread and Love films behind; Tutti a Casa is one of the crueler comedies, along with L'Ingorgo (June 27).