Democratic Assemblywoman Sally Lieber said such a law is needed because spanking victimizes helpless children and breeds violence in society.
"I think it's pretty hard to argue you need to beat a child," Lieber said. "Is it OK to whip a 1-year-old or a 6-month-old or a newborn?"
Lieber said her proposal would make spanking, hitting and slapping a child under 4-years-old a misdemeanor. Adults could face up to a year in jail and a $1,000 fine.
Aides to the assemblywoman said they are still working on a definition for spanking.
Some Republican lawmakers called the idea ridiculous. But Gov. Arnold Schwarzenegger said he may be receptive to it even though he has concerns about how the ban would be enforced.
The governor said he and his wife, Maria Shriver, did not spank their four children and used alternative methods for discipline. For example, Schwarzenegger said they found it more effective to threaten to take away their children's play time if they didn't do school work.
"They hate that much more than getting spanked," he told reporters Friday in Los Angeles.
California law permits spanking by parents unless the degree of force is excessive or not appropriate for the child's age.