At a time when surveys show teenage drug use dropping nationally, Herndon High School officials say they recommended more students for expulsion on drug charges during the fall than all of the previous school year.

The increase has alarmed school officials. Principal Janice Leslie and PTSA President Lisa Lombardozzi have posted digital letters to parents and area residents asking for their help. Herndon High's 2,309 students come from the Herndon, Reston and Dranesville area.

"The drug activity spans grade levels, income levels and neighborhoods," Leslie wrote in her letter, posted on the school's Web site, www.fcps.edu/HerndonHS.

"We have had to discuss drug problems with students slated to earn advanced studies diplomas and advanced placement diplomas. We have dealt with drug use with National Merit scholars and we've seen it with ninth graders on the first day of school," she wrote.

Since September, Leslie said, 12 students have been recommended for expulsion for drug use or possession, mostly marijuana, and another dozen cases are pending. In the nine-month 2001-02 school year, she said, about eight students faced the same punishment.

Leslie and Lombardozzi said they believe the increase in marijuana-related expulsions was a problem shared by other schools in the western part of the county. The principals at South Lakes and Chantilly high schools, however, said there had been no dramatic spike in the number of such infractions this year at their schools. Pamela Latt, principal at Centreville High School, said that no students have been recommended for expulsion for marijuana this year.

Only Westfield High School's principal, Dale Rumberger, said the number of drug expulsions at Westfield would probably soon exceed last year's figure.

He said he was concerned that students who are using or selling drugs "are more deeply involved and more brazen" than in the past. Rumberger also said he believes that school officials' efforts to protect students from the dangers of substance abuse were hampered by parents and community members in denial about the pervasiveness of the problem and the potential for any child to succumb to the lures of drugs.

According to a recently released survey, teenage drug use is dropping nationwide. The study, conducted by the University of Michigan's Institute for Social Research, said the number of U.S. high school seniors who admitted to using marijuana in the 30 days preceding the survey dropped almost a full percentage point, from 22.4 percent in 2001 to 21.5 percent in 2002. The annual study, called "Monitoring the Future," has been conducted for the National Institute on Drug Abuse since 1975.

County school officials recommended 307 students for expulsion for drugs and alcohol during the 2000-01 year, according to school system spokesman Paul Regnier. That number dropped to 239 students in 2001-02. County police said that although the figures for calendar year 2002 are not yet available, the number of juvenile drug arrests has also dropped in recent years, with 380 such arrests in 2000 and 303 last year.

The sudden spike in the number of drug-related problems at Herndon High and the diverse backgrounds of the students involved have left some people looking for an explanation.

Leslie declined to speculate on how the marijuana was getting into the students' hands or on the source of the drugs.

"I'm not a detective," she said. "Obviously the kids aren't growing it in the basement."

In her letter, Leslie described the efforts she and her staff have taken to combat the problem, including talking with the students and using forums such as science classes to discuss some of the potential harmful effects of drug use. She also appealed to parents to be more vigilant and active about their childrens' activities.

The principal emphasized that the number of students disciplined for drug-related incidents made up less than 1 percent of the school's enrollment.