LOS ANGELES — Violent dramas on the broadcast networks carry milder parental cautions than cable shows but can equal them in graphic gore, a failure of the TV ratings system, a new study found.

Scenes of stabbings, shootings, rape, decapitation and mutilation invariably received a TV-14 “parents strongly cautioned” rating on network TV, according to the Parents Television Council study released today.

But similar fare on cable typically was given the most stringent label, TV-MA for mature audiences only, researchers for the media watchdog group found.

“There are zero-point-zero series rated TV-MA on broadcast,” said the media watchdog council President Tim Winter, despite programs that are awash in violent scenes.

It is vital to examine the media’s effect on children and real-world violence, Winter said.

The study of 14 series during a four-week period found a 6 percent difference in the overall incidence of violence of all types on cable versus broadcast, with 1,482 violent acts on the cable programs and 1,392 on the network series.

Federally regulated broadcasters face sanctions if they cross the line on indecency or expletives, but not violence.

Episode ratings are decided by networks and cable channels, similar to how the movie studios’ Motion Picture Association of America self-governs by issuing its own movie ratings. The TV Parental Guidelines Monitoring Board, comprised of TV industry members and public interest advocates, checks for ratings uniformity and responds to public complaints. It received 38 complaints in the past year.

The ratings system “serves as a valuable resource for parents and helps them make responsible viewing decisions based on what is appropriate for their own families. The industry regularly reviews the TV ratings to ensure they continue to be useful to parents,” Missi Tessier, spokeswoman for the board’s executive secretariat, said in response to the PTC study.