The attorneys general of 24 states sent a letter Tuesday to Motion Picture Assn. of America president Jack Valenti saying the industry should reduce the amount of smoking in films to prevent teens from taking up the habit.

The attorneys cited a June study from Dartmouth Medical School that said children who watch movies in which actors smoke heavily are three times more likely to smoke themselves than those exposed to less smoking onscreen.

“With this new evidence … the motion picture industry stands in a uniquely powerful position to bring about a profoundly beneficial impact on the health and well-being of millions of Americans,” the letter reads.

It does not offer any specific steps Valenti is asked to take.

“We’re not saying any law has been broken,” said Tom Dresslar, a spokesman for California Attorney General Bill Lockyer, one of the officials who signed the letter. “We’re just asking out of a concern for the health of our kids that the industry do what it can to ensure that kids don’t start smoking.”

MPAA spokesman Rich Taylor said Valenti had received the letter and would respond appropriately.

“Smoking is, if you’ll recall, a legal activity,” he said, when asked what the MPAA was doing to reduce teen smoking. “That being said, he’ll be reading carefully the letter and the study it references.”

Brendan McCormick, a spokesman for Philip Morris USA, said the major tobacco companies agreed in the nationwide settlement signed in 1998 not to pay for product placement or to grant permission to films that want to feature their cigarettes. He declined to comment on the letter.

Dr. James Sargent, a pediatrician who was the lead investigator in the Dartmouth study, said Valenti should seek a change in the MPAA’s ratings system so films with smoking get an R rating.

He said if studios are willing to recut movies’ endings because focus groups don’t like them, they should be willing to cut smoking to protect children.

“If Valenti required movies to be rated R for smoking, if they incorporated that into their guidelines, smoking would disappear from PG, PG-13 and G movies overnight,” Sargent said. “That’s all he’s got to do.”

Sargent said smoking was more harmful for children than the violence, language and sexual content that typically earns films the R rating.

“Half a million people die a year from smoking,” he said. “If a movie contains the f-word it gets an R rating, and I don’t know of anybody that’s been harmed from profanity.”

The Dartmouth study involved 2,603 children who were between 10 and 14 at the start of the study in 1999 and had never smoked when they were recruited. They were asked at the beginning of the study which movies they had seen from a list of 50 movies released between 1988 and 1999.

Investigators counted the number of times smoking was depicted and determined how many smoking incidents each of the adolescents had seen. Exposure was categorized into four groups, with the lowest level involving between zero and 531 occurrences of smoking and the highest involving between 1,665 and 5,308 incidents.

Twenty-two of those exposed to the least onscreen smoking took up the habit, compared with 107 in the highest exposure group — a fivefold difference.

However, after taking into account factors known to be linked with starting smoking, such as sensation-seeking, rebelliousness or having a friend or relative who smokes, the real effect was reduced to a threefold difference.

The researchers also concluded 52% of the startup in smoking could be attributed to the movies.

The letter to Valenti was signed by the attorneys general of Arkansas, California, Colorado, Connecticut, Hawaii, Illinois, Maine, Maryland, Massachusetts, Minnesota, Mississippi, New Hampshire, New Jersey, New Mexico, New York, Ohio, Oklahoma, Oregon, Pennsylvania, Tennessee, Utah, Vermont, Washington and West Virginia.