Slightly more U.S. teens are smoking cigarettes, researchers reported on Thursday in a study they say suggests efforts to stop children from smoking have stalled.

The latest analysis by the Centers for Disease Control and Prevention finds the percentage of high school students reporting that they have smoked cigarettes in the past month increased to 23 percent in 2005 from 21.9 percent in 2003.

The increase is the first since a steady 40 percent decline in high school smoking rates between 1997, when 36.4 percent of high school students smoked, and 2003.

“The national decline in youth smoking observed during 1997 to 2003 might have stalled,” the CDC writes in its weekly report.

There are several possible reasons, said Dr. Terry Pechachek of the CDC’s Office of Smoking and Health. For one, states have not been consistently raising taxes on cigarettes, although such tax increases have been shown to reduce youth smoking.

States are also not funding educational campaigns in schools and the media like they used to, he said.

And, the researchers noted in the report, there have been “substantial increases in tobacco industry expenditures on tobacco advertising and promotion in the United States, from $5.7 billion in 1997 to $15.2 billion in 2003.”

“Additionally, after decades of decline, smoking in movies, which has been linked to youth smoking, increased rapidly beginning in the early 1990s and by 2002 was at levels observed in 1950,” they wrote.

Pechachek said the report may be a wake-up call to public health officials.

“We have to keep our eye on the ball ... applying what we know works,” he said in a telephone interview.

“In the most recent data released out of California for the year 2004, using comparable methodology to that released today, the prevalence of teen smoking is 13.2 percent,” he noted.

“That is an example of what can be attained if we keep our eye on the problem. Not only do they have good programs but they also have sustained the programs in the past 15 years.”

Smoking is the leading cause of preventable death in the United States and the world, causing heart disease, several kinds of cancer, emphysema and other diseases. Both smokers and those who have to breathe their smoke are affected.

Pechachek said stopping youths from smoking is key because about 80 percent of smokers started before age 18.

There is one small piece of good news. Smoking rates declined among black teens from 19 percent in 2003 to 14 percent in 2005.

Tobacco companies won a big victory on Thursday - the Florida Supreme Court declined to reinstate a $145 billion, class action damages award against major cigarette makers found liable for selling a dangerous product.

Pechachek said it was not immediately clear what effects the ruling might have on smoking cessation campaigns.