WASHINGTON — Movies and cigarettes have long gone together like Bogey and Bacall, but after years of pressure from advocacy groups, films will now get tougher ratings if their characters light up.

The Motion Picture Association of America announced yesterday that smoking will be considered when rating movies and “depictions that glamorize smoking or movies that feature pervasive smoking outside of an historic or other mitigating context may receive a higher rating.”

Smoking will become a factor in decisions by the Classification and Rating Administration, along with violence, language, nudity, drug abuse, and other elements.

“There is broad awareness of smoking as a unique public health concern due to nicotine’s highly addictive nature, and no parent wants their child to take up the habit,” MPAA Chief Executive Dan Glickman said. “The appropriate response of the rating system is to give more information to parents on this issue.”

But the MPAA resisted calls by some anti-smoking advocacy groups to give any film with smoking a mandatory “R” rating, meaning children under 17 would not be allowed to see it without a parent or guardian. Mr. Glickman said such a move is unnecessary.

According to a review by the ratings board, the percentage of movies with “even a fleeting glimpse of smoking ” dropped from 60% in July 2004 to 52% in July 2006, he said. Of the movies with smoking, three quarters received an R rating anyway for other adult themes.

Films whose ratings are affected by smoking will include explanations, such as “glamorized smoking” or “pervasive smoking.” The Classification and Rating Administration, a group of 10 to 13 parents whose chairman is appointed by the MPAA, previously had taken smoking into account only when it involved children under 18 years old.

Pressure had been building on Hollywood to do something about smoking in movies, which studies have shown make children more likely to try cigarettes. This month, 32 state attorneys general publicly called for the MPAA to give movies containing smoking an R rating unless they reflect the dangers of the habit or portray a historical figure.

The attorneys general based their call on recommendations from the Harvard School of Public Health. Mr. Glickman had asked the school last fall to study the effect of smoking in movies. Their findings, presented to the MPAA in February, found urgent action was needed.

Research published this month by the Dartmouth Medical School found that 74% of 534 recent box-office hit movies contained smoking. Many of the movies were rated PG-13.

In a study of German teenagers, researchers found those who had seen the most smoking in movies — usually major Hollywood films — were nearly twice as likely to have tried cigarettes as those who saw the least amount of on-screen smoking.

Those findings mirrored a 2003 U.S. study by Dartmouth that seeing smoking in movies nearly tripled the risk that children aged 10 to 14 they would try cigarettes. Last year, the Centers for Disease Control noted that after decades of decline, smoking in movies “increased rapidly” in the late 1990s and in 2002 was at the same level as in 1950.

It cited increases in movie smoking for the leveling out of cigarette use among high school students from 2003 to 2005 after several years of significant decreases.