She is the Reagan administration's newest recruit in its war against illegal drugs.

"I'm curious to know how you got started." Nancy Reagan yesterday told several dozen residents of Second Genesis, a nonprofit drug rehabilitation and treatment center at Upper Marlboro. It's one of several in the Washington area for 14 to 38-year-olds seeking a second chance for a life free of drugs.

After six weeks of meetings with experts in drug enforcement and education, the first lady was seeing for herself what is being done for drug abusers and offenders. She had a number of questions, she said, sitting among them for what became a rap session on what went wrong and why.

Had most of them started out on pot?she wanted to know. Had most of their parents realized they were using drugs? Did they think marijuana should be legalized?

"Absolutely not," they chorused in answer to her third question.

"I never go to any of these programs without asking that," she said. "And the answer is always the same."

Something else that bothered her was what one youthful resident described as the glorification of drug use by the television and motion picture industries.

"I just couldn't agree with you more," she said. "When I've read interviews with people who say they come home and have a 'joint' to relax, you wonder what in the world they are thinking of."

What also alarms her she said, is the idea that marijuana is harmless.

"It seems to me it is very difficult to convince a lot of young people that it is harmful. What are your suggestions for getting this through to them?" she asked.

"Well, I'm not sure about the medical facts," replied one young man, "but I know it's harmful because it makes you apathetic. It's a coward's way out of your problems."

At the end, everybody held hands, sang the Carole King song "You've Got a Friend," then took the first lady outdoors to see their vegetable garden. Among her escorts were Genesis staff members and volunteers, including Dr. Sidney Shankman, executive director; Dr. Alan M. Rochlin, deputy Ruth Cavanagh, community relations coordinator; and advisory board members Aileen Train and Anne Richardson, who first brought the program to her attention.