A group of Charles County teen-agers and the county chapter of an antidrug group called The Chemical People will sponsor a "drug-free" dance for county high school students next week at which drugs will be banned and efforts made to stop smoking and drinking.

The students say they hope that the video dance at La Plata High, which will feature a disc jockey, will start a trend. They say they are attempting to avoid the dance floor fights and dope-and-drinking parties in school parking lots that have marred other dances in the county.

The students even invited the president's wife, Nancy Reagan, to the affair Saturday because of her antidrug activities.

"We're practically in her back yard," said Sgt. Edward Keyton, who is a member of the county sheriff's department, The Chemical People and the Waldorf Jaycees, whose money is helping to pay for the dance.

The Chemical People organized in the wake of television programs aired more than a year ago that described growing drug and alcohol abuse among young people. Nancy Reagan appeared on the shows, but a White House press officer said she was not planning to attend the dance.

Although drinking and drug use have always been forbidden in Maryland high schools, teen-agers have traditionally found a way around the rules and laws, students here said.

In December, a Christmas dance at La Plata was canceled an hour after it began because of fist fights among students, said Julie Smith, sophomore class president and head of the video dance committee.

"Some of the kids were drunk or on drugs. They probably didn't really know what they were doing . . . . We just want to show people that there are a lot of kids out here who just want to come to a nice dance and dance."

At La Plata's upcoming dance, no one will be allowed in who looks drunk or drugged, nor will students be allowed to smoke cigarettes anywhere near the school.

"They've had drug-free proms in St. Mary's and Montgomery counties where the kids were bused off school property for the evening, but this is the first major activity of this sort that The Chemical People has put together," said Christopher L. Faegre, regional prevention coordinator with the state's alcoholism and drug abuse administration.

"Creating a climate where straight kids can have clean events has been the toughest thing in the past 10 or so years," Faegre said. ". . . But you can publicize that it is intended as a clean event. The publicity alone tends to shake out the drug-using population."

Extra chaperones and off-duty police officers will be on hand to patrol parking lots and playing fields at the high school where carloads of students with six-packs and drugs congregate, Keyton said.

Smith, 15, said that when Keyton and The Chemical People approached the students with the idea, "it was too good to pass up . . . . They're paying for everything. We are just trying to play up the drug-free aspect and convince people to participate."

Faegre thinks the idea will catch on because of the new emphasis on "wellness."

"Kids are more into overall fitness now. They are turning on to vegetarian foods, no smoking . . . turning their backs on all of the chemicals and additives our society offers.

"We're really trying to turn the clock back to the '50s and early '60s, when kids felt school was a controlled and safe environment."

The dance Saturday is open to all county high school students. Tickets are $2.50 for La Plata students and $3 for others, Smith said.