WASHINGTON — Americans over 50 are living longer, smoking less and developing fewer disabilities than their predecessors, but increasing obesity could cancel the health gains, an AARP report says.

Obesity among those over 50 nearly doubled from 1982 to 1999, to 26.7 percent of that population from 14.4 percent, said the report being released Tuesday.

On the other hand, the study found that, over the past decade, smoking among men and women over 50 has decreased 29 percent. More women are getting mammograms, and more older Americans report getting preventive services like blood pressure checks, cholesterol screening and prostate exams.

Susan Raetzman, associate director of the AARP's Public Policy Institute, said the obesity problem "threatens to outweigh the gains in prevention of other diseases."

The AARP report is based on research from as far back as 20 years ago as well as new surveys and data commissioned by the organization.

Among other findings:

More people between the ages of 50 and 64 are uninsured today than in the past. AARP cites less health coverage by employers for early retirees and gaps in Medicare coverage, including the lack of a prescription drug benefit.

Health costs are increasing for those over 50. Between 1977 and 1996, health-care spending for that age group increased 310 percent, almost twice as fast as inflation. Prescription drugs are accounting for more and more of the increase.

Americans ages 50-64 tend to be more skeptical about the health-care system than those over 65. They are less likely to believe their doctors will tell them about medical mistakes and more likely to obtain medical information over the Internet.

The findings on obesity come at a time when American and world leaders are voicing concern about the problem.

Reports have shown that some 60 percent of U.S. adults are overweight or obese, as are nearly 13 percent of children.

Just last week, the World Health Organization decided to take a more aggressive approach in trying to head off obesity-related diseases like high blood pressure, diabetes and heart disease.

The organization, which estimates that 300 million people worldwide are obese and 750 million more are overweight, is trying to work with food producers on a solution to the problem.

In the United States, preventable obesity, Type 2 diabetes and tobacco-caused illnesses cost the nation $270 billion a year in medical bills and lost productivity — more than the entire annual budget for Medicare, according to Health and Human Services Secretary Tommy Thompson. Medicare is the nation's health insurance program for the elderly and disabled.

The government has launched a $20 million project in five communities to cut residents' obesity and diabetes. And Thompson plans to push big employers to offer workers exercise time and facilities and to ask insurance companies to fund major anti-fat ad campaigns.

AARP has launched its own pilot project to promote physical activity among older Americans. The project, operating in Richmond, Va. and Madison, Wis., will push the 50-and-over set to engage in at least 30 minutes of activity five times a week. The organization hopes to take the project nationwide.

On the Net: www.aarp.org