WASHINGTON -- One in 12 full-time workers in the United States acknowledges having used illegal drugs in the past month, the government reports.

Most of those who report using illicit drugs are employed full time, with the highest rates among restaurant workers, 17.4 percent, and construction workers, 15.1 percent, according to a federal study released yesterday. About 4 percent of teachers and social service workers reported using illegal drugs in the past month, which was among the lowest rates. The overall usage rate is 8.2 percent.

The latest study comes from the Substance Abuse and Mental Health Administration, an agency within the Health and Human Services Department. The data is drawn from the agency's annual surveys in 2002, 2003 and 2004 of the civilian, noninstitutionalized population. Each survey included interviews with more than 40,000 people, who were each paid $30 to participate.

Joe Gfroerer, an agency official, said most of the illicit drug use involved marijuana.

Anne Skinstad, a researcher and clinical psychologist, called the survey's results "very worrisome" because there are fewer treatment programs than there used to be to assist employees and employers with a dependence on drugs.

However, testing programs for drug use are fairly prevalent, with 48.8 percent of full-time workers telling the government that their employers conducted testing for drug use.

"Some employers want drug testing. I'm not sure that's the way I would like to go. What I think I would like to focus on is employee performance," said Ms. Skinstad, an associate professor and director of the Prairielands Addiction Technology Transfer Center at the University of Iowa.

The study also showed that the prevalence of illegal drug use reported by full-time workers in the past month was highest among younger workers.

Nineteen percent of workers ages 18 to 25 said they used illegal drugs during the past month, compared with 10.3 percent among those ages 26 to 34; 7 percent among those ages 35 to 49; and 2.6 percent among those ages 50 to 64.

Men accounted for about two-thirds of the workers -- 6.4 million -- who reported using illegal drugs in the past month, the government said.

The study also looked at alcohol use by workers. About 10.1 million full-time workers, or 8.8 percent, reported heavy alcohol use. Heavy alcohol use was defined as drinking five or more drinks on one occasion at least five times in the past 30 days.