PHILADELPHIA (AP) _ Investigators offered three possible motives for the botched Halloween night shooting of a son of jailed mob boss Nicodemo ''Little Nicky'' Scarfo - revenge against the father or battles for power or turf.

Nicodemo Scarfo Jr., 24, was recuperating under police guard today at Thomas Jefferson University Hospital after being shot by a masked man as he dined at an Italian restaurant. Scarfo was knocked out of his chair, falling face down in a pool of blood and tomato sauce.

Dr. Jerome Vernick, director of the hospital's trauma center, said Scarfo was hit by at least four bullets, in the arm, behind the ear, in the shoulder and in the chest. He said Scarfo was in fair condition.

Police said he may have been shot for revenge against the failure of his father, who headed the Philadelphia-southern New Jersey mob for nearly a decade, to keep his Mafia members from becoming government informants.

At least five already have given the authorities information that has helped result in the convictions of the elder Scarfo and about two dozen of his men on assorted charges, including racketeering, murder and extortion.

When the 60-year-old Scarfo was sentenced to 69 years in the federal penitentiary at Marion, Ill., some sources said his middle son, Nicodemo Jr., sought to take over his father's gambling and loan sharking activities.

Young Scarfo, known for his wraparound sunglasses and slicked-back hair, was said by acquaintances to relish his closeness to the mob throne.

Louis Pichini of the U.S. Organized Crime Strike Force said there were three possibilities of why young Scarfo was shot.

''One is that he could have been the victim of an internal struggle to take over what was left of Scarfo's organization,'' Pichini said.

''Second, he could have been the victim of outside mob forces from New York trying to move in and he was representative of the existing group here, or what was left of it.

''And the third possibility is that those mobsters in New York were upset about the number of defectors in the Philadelphia organization and Scarfo's lack of control, and were retaliating with a deadly message to show they didn't like it one bit.''

A half-dozen police officers guarded Scarfo in the hospital.