FEW EXPERTS on teen-age drug abuse can tell us with certainty how many youths are experimenting or regularly using illicit drugs. Fewer still would be able to walk into a school and persuade anyone to come forward and admit to a drug problem. That is part of what was so remarkable about what the Rev. Jesse Jackson accomplished at the District's Spingarn High School last Thursday.

Standing before an audience of about 900 pupils, turning what was meant to be a salute to the school's basketball team into something like a revival meeting, Mr. Jackson asked every student who was using drugs to step forward. One hundred students did. The number was staggering, especially when you consider that there were undoubtedly others in the audience who were afraid or did not want to be recognize.

A very great number of young people in the District come in contact with drug abuse every day of their lives. Statistics from the National Institute on Drug Abuse show that 86 percent of the nation's high school seniors know that illicit drugs are easily obtained. About 63 percent have used drugs. And children as young as 5, if they witness the regular use of drugs, can begin to believe that it is an acceptable practice.

Mr. Jackson has done a service to Spingarn. Principal Clemmie Strayhorn says the school already has a program run by an athletic coach that teaches teen-agers how to counsel their peers on drug use. And the school system as a whole has other programs, such as one being tried at six schools that teaches youths to say no to drug abuse. But these measures are largely designed to prevent drug abuse before it occurs.

District School Superintendent Floretta D. McKenzie believes that District government agencies should help the school system deal with regular drug abusers, and school board member Eugene Kinlow, chairman of the board's student services committee, says the students at Spingarn raise concerns about the pervasiveness of drug use in the rest of the city's high schools. What is of paramount importance now is that the opportunity be seized to help 100 students who have asked for that help.

"We are going to embrace these young people," Mr. Strayhorn says. "We can't afford to lose these children."