Ratings to Give Parents More Data : Movies: The new system, devised by the MPAA and NATO, offers explanations on why films are rated PG and PG-13.

Coming to theaters soon: More information for parents about movies.

The Motion Picture Assn. of America and the National Assn. of Theatre Owners, which administer the movie rating system, said Tuesday they will begin providing explanations of why movies are rated PG (parental guidance suggested) and PG-13 (parents are “strongly cautioned . . . some material may be inappropriate for children under 13”).

Until now, the adult categories, R and NC-17, have been the only two to include an explanatory note stating the rationale for the rating decision. For example, the erotic thriller “Basic Instinct” received an R rating and carried the explanation that the movie contains “strong violence and sensuality” and “drug use and language.”

In contrast, no explanation was offered to parents to describe the PG-13 rating of the current “Batman Returns.” Some parents have expressed confusion about the film’s suitability for young children because it is being marketed for all ages. The new system would have given parents more information about the movie.

MPAA President Jack Valenti said the timing of the new policy is “coincident” with the current national political debate about family issues and some conservatives’ criticism that the entertainment industry is indifferent to “family values.”

The move is the first adjustment to the 24-year-old voluntary movie rating system since September, 1990, when the NC-17 label replaced what formerly had been the “X” rating for adults-only fare. At that time, the MPAA began sending out explanations of the R and NC-17 ratings to theaters, film critics and to video retailers.

“Our feedback from parents and exhibitors indicates they have been pleased with the explanations on R-rated movies,” Valenti said. “Now we want to extend it to the other ratings.”

No explanatory statements will accompany the G rating, which advises that a movie is considered acceptable for all age groups.

William F. Kartozian, president of the National Assn. of Theatre Owners, representing more than half of the 23,000 screens in the United States, said the change is a response to “trends in the nation, and this is what we can do to make ourselves more user-friendly.”

Kathryn Whitfill, first vice president of the National Parent Teachers Assn., said by phone from her Houston-area home: “Anything that will help parents to decide what movies their children can see is of value. If the one-line explanation really tells the parents what to expect, it’s an asset.”

Among the first films to receive the new explanations in this week’s list of newly rated movies is Warner Bros.’ “Christopher Columbus: The Discovery,” starring Tom Selleck and Marlon Brando, due in theaters Aug. 21. The film was rated PG-13, for “some action violence, and for nudity.”