WASHINGTON — Many of the nation's estimated 10.8 million underage drinkers are turning to their parents or other adults for free alcohol.

A government survey of teens from 2002 to 2006 said slightly more than half had engaged in underage drinking.

Asked about the source of alcohol, 40 percent said they got it from an adult for free over the past month, the survey said. Of those, about one in four said they got it from an unrelated adult, one in 16 got it from a parent or guardian, and one in 12 got it from another adult family member.

Roughly 4 percent reported taking the alcohol from their own home.

"In far too many instances, parents directly enable their children's underage drinking — in essence, encouraging them to risk their health and well-being," said acting Surgeon General Steven K. Galson. "Proper parental guidance alone may not be the complete solution to this devastating public health problem — but it is a critical part."

The nationwide study by the Substance Abuse and Mental Health Services Administration, being released today, tracks the social contexts involved in underage drinking, a problem leading to thousands of alcohol-related traffic deaths and injuries each year.

About one out of five of those ages 12 to 20 — or roughly 7.2 million people — said they had taken part in binge drinking, defined as consuming five or more drinks on at least one occasion in the past month, the survey said. Rates were significantly higher if they lived with a parent who engaged in binge drinking.

The study, which uses data from the National Surveys on Drug Use and Health, is based on a scientific random sample of 158,000 people ages 12 to 20 in the United States. Among the other findings: