One year after the television networks revised their movie-style ratings code to add labels alerting parents to sexual or violent content in shows, a study has found that the networks are not regularly adding those labels.

The labels, for example, V for violence or S for sexual content, are added to the age-group ratings printed in television listings and appearing on screen at the start of shows.The age-group rating codes are being applied appropriately to 96 percent of the programs, according to the study released Thursday by the Kaiser Family Foundation, a philanthropic group devoted to public health issues.

But the report by the foundation, based in Menlo Park, Calif., said 92 percent of shows with some sexual content did not carry the additional S label, and 79 percent of shows that had violent scenes did not carry a V. Also, the study found that 81 percent of children's shows that contained violence did not have the FV notation, for fantasy violence, which is found to varying degrees in many cartoons.

Those percentages may be skewed upward by the fact that NBC programming was included in the study's sample, and NBC has refused from the outset to add the V, S, L for foul language and D for suggestive dialogue to the system. And the study acknowledged that some violent or sexual content not labeled was of "low level."

The age-based labels, in use since January 1997, are supposed to be applied to all programs except news and sports. They are TV-G for all ages; TV-PG, parental guidance suggested; TV-14, not suitable for those under 14; TV-MA, for adults only; TV-Y, for all children, and TV-Y7, may not be suitable for children under 7.

A year ago, all networks except NBC and the cable network BET agreed to augment their age-group ratings with the four letters to signal what specific content in a show might be found objectionable.

"If the ratings are misleading or not being applied accurately, then the system won't work for parents," said Kathryn Montgomery, president of the Center for Media Education. "We need some close scrutiny from the monitoring board."