“You don’t know you’ve crossed the line until you get accused of crossing the line,” he said.

Whether Cesar Rodriguez, who is accused of beatings and abusive behavior that killed his 7-year-old stepdaughter, could not have known he had crossed a line is a matter for a jury to decide. He has admitted that he routinely beat Nixzmary with a belt, hit her with his hands using “all my force,” threw her on the floor. He has admitted duct-taping her emaciated 37-pound frame to a chair and binding her with bungee cords.

But at least in a broad legal sense, Mr. Schwartz has a point. The laws in New York State, as in the rest of the country, are vague on corporal punishment.

Parents in all 50 states are allowed to hit their children. In his opening argument, Mr. Schwartz reminded the jurors that most of them had said during jury selection that they had been hit as children and noted that parents have widely varying styles of discipline.

There are limits, of course, on what is allowed. But out of reluctance to legislate parental conduct, state lawmakers have shied away from getting too specific about those limits, instead letting courts consider the matter case by case.

Consider some of the cases cited in the Legal Aid Society’s training guide for its lawyers who work in New York’s Family Courts.

In one case, inflicting cuts and bruises on a child was deemed “excessive corporal punishment,” amounting to neglect, the most basic and frequently charged form of child mistreatment. But in another case, shaking a child and causing her to hit her head on the pavement was ruled allowable.

Hitting a 9-year-old with the buckle end of a purse strap for leaving his 2-year-old sister alone in a room was acceptable. Hitting a child with a belt for lying on the floor, kicking a table and peeling paint off a wall was not.

Leaving red marks on the face of a 13-month-old constituted neglect. Dragging an 11-year-old out of a car by the collar, scraping his neck, and throwing him on the ground, scraping his knee, did not.

In a case where a father was charged with abuse, a more severe infraction than neglect, judges held that biting a girl on the face and arm, leaving severe bruises, did not cross the line. In this context, the threshold for abuse was intentionally causing or risking a physical injury that involved disfigurement or “protracted impairment of physical or emotional health.”

Stephen P. Forrester, who runs the child abuse identification training program for the New York Society for the Prevention of Cruelty to Children, said that in trying to decide whether corporal punishment has crossed the line into abuse, he advises considering several factors.

These include the severity of the beatings, the frequency of punishment (“Once or twice might be reasonable,” Mr. Forrester said, “but 35 times is beyond the pale”), the age of the child, and the location of the bruises.

Criminal prosecutions for corporal punishment are rare, several experts said, largely because the law grants parents a wide exception to the assault statutes. However, such parents might lose custody in Family Court, where the main standard is the welfare of the child. In New York, parents may “use physical force,” as long as it is not deadly, to the extent that they reasonably believe necessary “to maintain discipline or to promote the welfare” of a child.

Mr. Schwartz is arguing that Mr. Rodriguez, 29, was not acting recklessly or with “depraved indifference” to Nixzmary’s life, as prosecutors claim in the second-degree murder charge he faces.

The thrust of his defense is that Mr. Rodriguez gave Nixzmary the same kind of discipline that Mr. Rodriguez’s father had given him, including hitting him a lot and holding his head under cold water. This corrected Mr. Rodriguez’s waywardness and helped him grow up to be a decent father who took Nixzmary and the other children to parks, helped them with homework, and tried things like timeouts before resorting to hitting, Mr. Schwartz argued.

Therefore, Mr. Schwartz is asking the jury to find, Mr. Rodriguez was reasonable in using his father’s disciplinary techniques on Nixzmary, including the cold-water treatment, which Mr. Rodriguez gave Nixzmary the night she died in January 2006.

“It was done to him, and it didn’t kill him,” Mr. Schwartz said outside the courtroom on Thursday. “How was he to know that it was something that would cause death?”

(If there were some things done to Nixzmary that were unallowable, Mr. Schwartz has said, they were done by Nixzmary’s mother, Nixzaliz Santiago, not by Mr. Rodriguez. She will be tried separately, also on a second-degree murder charge.)

While laws in the United States are broadly permissive, a number of countries take a dimmer view of parental corporal punishment. Twenty-three of them have passed bans on it, including, in 2007 alone, Chile, the Netherlands, New Zealand, Spain and Venezuela, said Susan H. Bitensky, a professor at the Michigan State University College of Law.

The bans tend not to be strictly enforced, Professor Bitensky said. Since Sweden passed its law in 1979, fewer than five parents have been prosecuted for moderate or light corporal punishment, she said. “These countries are relying on the pedagogical or didactic value of these laws to make the hitting of children socially unacceptable,” she said.

But in the United States, any legislative gesture, symbolic or otherwise, aimed at blocking parents from hitting their children is greeted with catcalls. In California last year, a bill to criminalize parental discipline involving a closed fist, belt, electrical cord, shoe or other objects punishment was all but jeered out of the State Legislature and quickly abandoned. An antispanking bill in Massachusetts appears headed for a similar fate.

A hole in Minnesota’s laws leaves parents who hit their children open to assault charges, said Victor Vieth, a former prosecutor who now directs the National Child Protection Training Center, which trains investigators on child abuse cases.

“But there’s been no uproar, because no one would pursue mild forms of corporal punishment,” Mr. Vieth said. “I don’t know of a single instance where anybody was prosecuted for a mild form of corporal punishment.” Indeed, a state appeals court in Minnesota recently ruled that a father’s giving his 12-year-old son 36 strokes with a wooden paddle was not even a civil offense.

To draw a bright line in the law, said Martin Guggenheim, a professor at New York University School of Law, would be to cross the threshold of what the United States Supreme Court once called “the private realm of family life which the state may not enter,” and to intrude on parents’ constitutional right to raise children as they see fit.

“It’s a huge challenge to draft a law that allows parents to engage in corporal punishment, but at the same time to clarify in advance what is unacceptable, what is impermissible,” he said. “The best we have come up with is to say that when it’s excessive, it’s impermissible.”

Correction: January 25, 2008

An article on Sunday about the legal limits of corporal punishment, an issue raised in the murder trial of Cesar Rodriguez of Brooklyn, accused of beating his 7-year-old stepdaughter to death, referred imprecisely to a bill introduced in the California Assembly last year. The bill, which was abandoned, would have criminalized parental discipline involving a closed fist, belt, electrical cord, shoe or other objects, but it would not have outlawed “all corporal punishment.”

An article on Sunday about the legal limits of corporal punishment, an issue raised in the murder trial of Cesar Rodriguez of Brooklyn, accused of beating his 7-year-old stepdaughter to death, referred imprecisely to a bill introduced in the California Assembly last year. The bill, which was abandoned, would have criminalized parental discipline involving a closed fist, belt, electrical cord, shoe or other objects, but it would not have outlawed “all corporal punishment.”