Washington ? America has almost 16 million illegal drug users, including one in five young adults, according to a government survey that suggests use of marijuana and cocaine may be on the rise after leveling off in recent years.

Among ages 12 to 17, the youngest people surveyed, 10.8 percent were described as current drug users in 2001, up from about 9.7 percent the year before, according to the National Household Survey on Drug Abuse.

Young adults ages 18 to 25 were more likely to be users, increasing to 18.8 percent from 15.9 percent in 2000. The rate of drug use among adults 26 and older stayed about the same, at 4.5 percent. Current users are those who reported using a drug within the past month.

Although a few drugs, including LSD, are diminishing in popularity, others are seeing big gains. The number of people who have tried Ecstasy increased from 6.5 million in 2000 to 8.1 million last year, the survey shows.

Nonmedical use of the pain reliever Oxycontin more than doubled, from 399,000 users in 2000 to 957,000 in 2001.

The survey shows moderate increases in the use of marijuana and cocaine by teenagers and young adults from 2000 to 2001. But researchers said it was too soon to tell whether that marks the reversal of a trend of stable or declining drug use since the late 1990s.

“It could continue up and be the start of a long-term trend, or it could go down again,” said Joe Gfroerer, director of the survey by the Substance Abuse and Mental Health Services Administration. “We don’t try to predict that.”

Other national surveys saw no statistically significant increase in drug use in 2001, and some even reported declines among young people. The National Household Survey on Drug Abuse is the largest study, interviewing almost 69,000 people age 12 or older and including every state.

Timing and varied methodologies often result in different results among surveys.

Health officials noted that the number of people who perceived smoking marijuana once or twice a week as risky dropped to 53 percent, and blamed baby boomer parents for failing to take the risks of pot-smoking seriously and warn their children.

“As the perception that marijuana is dangerous goes down, its use goes up,” observed Tommy Thompson, secretary of Health and Human Services, which oversaw the survey. “More than a quarter of first-time marijuana users are under 15.”