WASHINGTON (Reuters) - Nearly 21 percent of Americans smoke, a number that has been stalled since 2004, federal researchers reported on Thursday in a study they said means governments must spend more to persuade people to kick the habit.

More than 45 million Americans smoked in 2006, or 20.8 percent of the population, 80 percent of them daily smokers, the U.S. Centers for Disease Control and Prevention reported.
The CDC said the numbers have not changed since 2004, which suggests that smoking prevention efforts have ""stalled.""
""It is completely commensurate with the stall in resources that have been going into tobacco control,"" Dr. Matt McKenna, who directs CDC's Office on Smoking and Health, said in a telephone interview.
William Corr, executive director of the Campaign for Tobacco-Free Kids, agreed.
""It is troubling news for America's health that progress has stalled in reducing tobacco use, the nation's number one preventable cause of death,"" Corr said in a statement.
""It is also inexcusable that elected leaders have not done more given the overwhelming scientific evidence of what works to reduce tobacco use among both children and adults.""
The CDC researchers used the National Health Interview Survey of more than 24,000 U.S. adults to find out how many people smoke.
Nearly 24 percent of men and 18 percent of women smoked. Numbers ranged from more than 50 percent of men with a high school equivalency diploma, to 4.6 percent of Asian women. More educated people were less likely to smoke, with 6.6 percent of those with graduate degrees being smokers.
""Among current cigarette smokers, an estimated 44.2 percent (19.9 million) had stopped smoking for more than one day during the preceding 12 months because they were trying to quit,"" the CDC researchers wrote.
Half of the 91 million people who ever smoked had quit.
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""Cigarette smoking remains the leading preventable cause of disease and death in the United States, resulting in approximately 438,000 deaths annually,"" the CDC said.
McKenna said state and federal officials are not doing everything they can to help counter the efforts of tobacco companies.
While the CDC recommends spending $1.80 per person a year in Oregon, for instance, to encourage quitting, the tobacco industry spends $3.50 per person on marketing, he said.
""The overall CDC recommendations nationally for state programs to fund tobacco control is about $3.7 billion. Currently about half a billion dollars is being spent,"" he said.
Most of the $22 billion a year states get from a $246 billion 1998 ""master settlement agreement"" reached with tobacco companies goes not to tobacco prevention efforts, but to general spending such as road building, McKenna said.
""We know what to do,"" McKenna added. Media campaigns, tobacco taxes and subsidizing treatment all work, he said.
""Utah has a (smoking) prevalence rate of 9 percent. So the idea that there is an irreducible number of people who will smoke is probably true but it is much less than one in five people,"" he said.