ATLANTA - For the first time in nearly 50 years, the average cholesterol level for American adults is in the ideal range, the government reported yesterday.

A national survey that includes blood tests found the total average cholesterol level dropped to 199 last year from 222 when the survey began in 1960.

Experts consider 200 and lower to be ideal.

The growing use of cholesterol-lowering pills in middle-aged and older people is believed to be a key reason for the improvement, experts said. Indeed, cholesterol levels for younger groups hardly changed.

While Americans have gotten much heavier since 1960, they have been able to lower their cholesterol with powerful drugs that carry few if any side effects. High cholesterol can clog arteries and lead to heart disease.

Doctors groups have increasingly recommended more aggressive use of these drugs in patients seen to be at risk from heart disease. And screening has become common - two-thirds of men and three-fourths of women had been screened for high cholesterol in the previous five years, according to the Centers for Disease Control and Prevention.

The result: Cholesterol medications are the top-selling class of drugs in the United States, having grown steadily from about $13 billion in 2002 to nearly $22 billion in 2006, according to IMS Health, a consulting company that monitors pharmaceutical sales.

"There's been an explosion in the use of these medications, and appropriately so in the majority of cases," said Elizabeth Jackson, a preventive cardiologist at the University of Michigan Medical Center.

The CDC, which runs the cholesterol survey, collects data in two-year intervals. The new results are based on a national sample of about 4,500 people age 20 and older in 2005-06. The new level of 199 compares with 204 in 1999-2000.

Researchers also found that the percentage of adults with high cholesterol, 240 or higher, dropped to 16 percent from 20 percent in the early 1990s.

The biggest declines were in men aged 40 and older and women 60 and over.

"These age groups are the ones most likely to be treated with medication," said Susan Schober of the CDC's National Center for Health Statistics and lead author of the report.

There was little change in cholesterol levels for other age groups, prompting some experts to suspect the news might not be all good.

"This is kind of incomplete information," said Roger Blumenthal, a Johns Hopkins University cardiologist.

Total cholesterol is a summary of HDL, the so-called good cholesterol, and LDL, bad cholesterol, and a measure of triglycerides, a form of fat. Obesity rates in teens and young adults have been shooting up, and it's possible that they are experiencing gains in triglycerides and losses in beneficial cholesterol, said Blumenthal, who also is a spokesman for the American Heart Association.

"If you take away the people on medication," he said, "I don't think there's been as much of a meaningful improvement as we would like."

Among the best-known prescription drugs for lowering cholesterol are Lipitor, made by Pfizer Inc.; Zocor, by Merck & Co.; and Pravachol, from Bristol-Meyers Squibb.

Another is Mevacor. Merck hopes to begin selling it over the counter, but federal health officials worry that consumers without medical backgrounds will have difficulty determining if it's appropriate for them.