The first lady of Canada is a striking 32-year-old mother of three -- with her fourth on the way.

"I came to the conference because I think that the cornerstone of our foreign policy is that we're going to give everyone the benefit of the doubt, and we're going to have a close association with our friends and allies," says Mila Mulroney shortly after arriving here yesterday. "I think that this is a very kind gesture on the part of Mrs. Reagan, to first of all inform us about what is going on in the United Staes, and enlighten us about what is going on in the rest of world."

Mila Mulroney is the wife of Brian Mulroney, a member of the Progressive Conservative Party elected prime minister last September. She was born in Sarajevo, Yugoslavia, and moved to Montreal with her family when she was of school age. She met her husband while studying civil engineering at Montreal's Concordia University.

She says Canada's drug problem is "bigger than we'd like it to be," but that it "is not as big as in the United States," and believes that Canada's educational system for the young is helping to control the problem.

"We've been able to arrest, if not decrease, the use of drugs," she says. "We're educating our youths to know we are in charge of our own bodies. It's a wonderful method. It's run through Health and Welfare, and it's very positive."

The Mulroneys' oldest child, Caroline, is 10, so a worry over drugs hasn't affected the family as yet.

"We are a very open family and we encourage dialogue and we encourage questions, and certainly, my children are much more aware than I ever was," she says. "We haven't hit the drug stage yet, but I'm sure we will. It's not a class problem any longer. It crosses all boundaries."

Mulroney says she hopes to learn more about the problem while she is here.

"I'd like to have more of an awareness about what's going on," she says. "I can't tell you that I know everything about drugs or that I have all the answers. That's not to say that I will after the conference is over. But I think being aware is certainly better than not."