LOS ANGELES, Nov. 9 (Xinhua) -- The U.S. national smoking rates have remained steady at nearly 21 percent from 2004 to 2006 after declining for seven years,, according to a new study.

    This has prompted concern among federal health officials that progress in curtailing smoking has stalled, said the report by the national Centers for Disease Control and Prevention (CDC), which was published by the Los Angeles Times on Friday.

    Changes to tobacco marketing are the reason the number of smokers is remaining steady, said the report.

    Reduced spending on anti-tobacco campaigns and bigger marketing budgets from cigarette companies appeared to be the reasons for the leveling off, said the report

    "Smoking is still the No. 1 preventable cause of death," said Dr. Matt McKenna, director of the CDC's Office on Smoking and Health. "No other behavior kills so many people as tobacco, even with these low levels."

    About 438,000 Americans die each year because of tobacco use, the CDC said. The agency estimated that for every death, there are20 people living with a tobacco-related illness.

    U.S. smoking rates have been on a downward trend since a 1964 surgeon general report linked lung cancer and cigarette smoking. At the time, about 42 percent of American adults were smokers, according to a study conducted the following year.

    Between 1997 to 2004 -- the most recent period of consistent decline -- the proportion of U.S. adult smokers dropped from 24.7 percent to 20.9 percent.

    Over the decades, there have been occasional periods when the declines have appeared to stall, such as between 1995 and 1997, which also appeared to be tied to changes in tobacco marketing, McKenna said.

    The most recent period of leveling began in 2004, according to the report. The smoking rate was the same in 2005 and dropped 0.1 percent in 2006, which McKenna said was an insignificant decline.