TUESDAY, Sept. 6 (HealthDay News) -- The rate of smoking among U.S. adults has resumed its four-decade decline, and those who continue to light up appear to smoke less than previous generations, officials from the U.S. Centers for Disease Control and Prevention said Tuesday.

"For 40 years there was a consistent decline in the number of adults who smoked -- from 1964 to around 2005," CDC director Dr. Thomas R. Frieden said during a noon press conference releasing the results of the CDC's new report on smoking prevalence in the United States.

The downward trend stalled after 2005 and has since resumed, but at a pace "much slower than the rate of previous declines," he said.

The number of smokers age 18 and older inched down from 20.9 percent in 2005 to 20.6 percent in 2009 and 19.3 percent in 2010, according to the report. That's about 3 million fewer smokers than if there had been no decline, the researchers noted.

While the number of people who smoked a pack and a half or more a day fell substantially, those smoking less than a half pack a day increased, according to the report, which relied on data from the 2005-2010 National Health Interview Surveys and the 2010 Behavioral Risk Factor Surveillance System survey.

Smoking less doesn't save lives, Frieden said. "The only safe thing to do is to quit smoking entirely," Frieden said.

About 45 million Americans still light up regularly, the CDC said.

Smoking takes a significant health and economic toll, Dr. Timothy McAfee, director of CDC's Office on Smoking and Health, said during the press conference. "Smoking costs the U.S. about $193 billion annually, which is comprised of direct medical costs and lost productivity," he said.

Smoking bans, cigarette price hikes and aggressive media campaigns have proven to be effective tools in the war against smoking, the researchers said.

But McAfee noted that tobacco companies continue to spend billions on advertising and discounting cigarettes to offset the increased cost from tobacco taxes that have cut into smoking rates.

Coupled with the reductions in spending for tobacco cessation programs in many states, this industry funding keeps the decline among smokers creeping along very slowly, McAfee noted. If these non-smoking programs were fully funded, there would be a much more rapid decline in smoking, he suggested.

Also making it more difficult to quit are changes in cigarettes themselves, Frieden said. The CDC has found that "the industry has been able to change the way nicotine is inhaled and absorbed. So it is possible that the cigarette today may be even more addictive than 10 or 20 years ago," he explained.

"We have seen an increase in what is called free-nicotine, or essentially 'crack' nicotine, available for very rapid absorption through the lungs," Frieden added.

Phillip Morris USA said in a statement released Tuesday that it agrees with the overwhelming medical and scientific consensus that cigarette smoking is addictive. "It can be very difficult to quit smoking, but this should not deter smokers who want to quit from trying to do so," the company said. "We support a single, consistent public health message on the role of cigarette smoking in the development of disease in smokers, and on smoking and addiction."

The cigarette maker also noted in its statement that it had actively supported legislation for more than eight years that provides tough but reasonable federal regulation of tobacco products by the U.S. Food and Drug Administration.

The CDC researchers found that smoking rates varied by region, with more smokers in the Midwest (21.8 percent) and South (21 percent) than in other regions of the country.

Referring to the decline in smokers nationwide, Frieden said, "3 million fewer smokers is a very significant finding. About half of all smokers will be killed by tobacco if they don't quit. And about a third of all current smokers may die from cigarette use unless they quit promptly. So we are talking about preventing more than 1 million deaths because of that decline."

But while the number of smokers who smoked 30 or more cigarettes a day dropped from 12.7 percent in 2005 to 8.3 percent in 2010, those who smoked one to nine cigarettes a day jumped from 16.4 percent in 2005 to 21.8 percent in 2010, according to the report.

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For more information on quitting smoking, visit smokefree.gov.