What will Nancy and Raisa talk about?

No one is quite sure what Raisa Gorbacheva does when she's not accompanying her husband on foreign trips. Everyone knows what Nancy Reagan does.

While the President has been busy boning up for his summit meeting with Mikhail Gorbachev, Nancy Reagan has been hard at work at the activity that has consumed much of her time in the past few years -- putting the nation's spotlight on the need to combat drug abuse.

This week is certain to see an acceleration of preparations by the nation's first couple for the November event. But almost to the last moment, Mrs. Reagan has pursued her primary interest. Last week she addressed the conference here of the National Federation of Parents for Drug-Free Youth. Yesterday she accompanied the Princess of Wales to the Straight Drug Rehabilitation Center at Springfield, Va.

Is she preparing in any way for the summit?

``How can you prepare?'' she commented in a brief interview. ``I'm reading some books about Russia, but we're not going to Russia, we're going to Geneva.''

As for what she might talk about with Mrs. Gorbacheva (the final ``a'' feminizes her married name), this is clearly uncharted territory. ``Nobody knows very much about her,'' the First Lady said. ``She hasn't given any interviews and I don't know anything about her.''

Even during the summit visit to Geneva, however, Mrs. Reagan will pursue her interest in drug-abuse rehabilitation, visiting a drug center in Lausanne. Recently she was host for the First Ladies' Conference on Drug Abuse at the United Nations, the second such meeting she has promoted to widen international attention to drug addiction. Attended by the wives of 17 other world leaders, the conference clearly pleased Mrs. Reagan, who hopes there will be a follow-up.

``You have to keep working all the time,'' she remarked, because the ``other side'' -- the drug dealers and pushers -- are working all the time. ``We can't let down and become complacent and think, well, marijuana use is down so we can sit back and not work as hard,'' she said earnestly. ``It's not true. And overseas there's a lot to be done. They're just starting to get involved now.''

There is no doubt Mrs. Reagan has made an impact in the United States through her untiring efforts to curb drug and alcohol abuse among young people. Since becoming First Lady, according to a White House press release, she has traveled some 75,000 miles to 47 cities in 27 states and three foreign countries, visiting elementary and high schools, giving speeches, and taping special radio and TV programs to increase awareness of the problem.

These may be dry statistics, but behind them is heartfelt appreciation from mothers and others who struggle with an insidious problem.

``To have her involved is like the sky opening and the sunshine coming through the clouds,'' says Carolyn Burns of Spring Valley, Md., an official of the National Federation of Parents. ``She's been the greatest motivator for getting people involved.

``And I've been to things where she's cried, when she sees people in pain,'' says Mrs. Burns, two of whose sons have come out of drug addiction. ``This is for real. It's not a game or show.''

At last week's federation luncheon the conference participants gave Mrs. Reagan a standing ovation. ``Four or five years ago we had to fight to get into the media,'' said Melissa Fuller of Houston. ``Now they always find space and give us attention.''

Mrs. Reagan says her accomplishment over the past five years has been to see a growing recognition of the drug problem. ``More people are aware now,'' she commented as we rode back in her limousine to the White House from the luncheon event. ``I see more about it in television now, more people coming forward and talking about their addiction and what it did to their lives, their family relationships, and so on. There's great satisfaction in seeing the young people now.''

Mrs. Reagan suggested that ``knowledge'' is the most important factor in combating drug and alcohol abuse. When drugs hit the American scene in the 1960s, she said, no one knew anything about drug abuse. ``Therefore we didn't recognize the signs in children,'' she said, ``and we didn't know what to do.''

Parents, she said, must become more knowledgeable about drug-abuse symptoms. ``The signs . . . are so comparable to the signs of adolescence that they could think, well, this is just adolescence they're going through when really it isn't.''

American officials do not rule out that Mrs. Reagan's antidrug-abuse activities could be a topic of conversation when she meets Raisa Gorbacheva, but that would be a sensitive subject for her Soviet counterpart. The Soviet Union does have a drug problem, but it is of smaller proportions and the Soviets are reticent to talk about it. Alcoholism, on the other hand, is a widespread and acknowledged Soviet social problem, which Mr. Gorbachev is trying to tackle head on.

Mrs. Gorbacheva, for her part, has made a splash abroad by virtue of her stylish clothes and modern appearance and manner as she accompanies her husband. But in the Soviet Union there is no avenue for wives of leaders to become involved in philanthropic endeavors.

There is in fact a touch of irony about the two women who will become acquainted in Geneva, and it says something about the different societies from which they come.

While they share an interest in fashion and designers, Mrs. Reagan has successfully sought to dispel the early impression that she had no deeper interest or involvement. In the past year she has received considerable attention in the news media, which have commented favorably on her antidrug-related activities, her increased self-confidence, and her influence at the White House.

Mrs. Gorbacheva, on the other hand, who has the equivalent of an American doctorate in philosophy, seeks to convey to millions of her compatriots -- and to the Western world -- that the wives of Kremlin leaders can have a sense of style and conduct themselves with grace and distinction when they travel abroad. It's a matter of self-image and pride.

The First Lady said she hoped to find a point of mutual interest with Mrs. Gorbacheva. This is why she wrote her a letter inviting her to tea -- an invitation that has been accepted. ``She teaches Marxist philosophy, so we come from different sides,'' said Mrs. Reagan. ``But, yes, I'd like to find a point of contact.''

Among the books Mrs. Reagan has been reading are Suzanne Massie's ``Land of the Firebird'' and M. Hayward's ``Writers in Russia: 1917-1978,'' volumes that have also been on the President's reading list. Before leaving for Geneva, her aides indicate, she will be briefed about her meeting with Mrs. Gorbacheva.

``We don't know what the conversation will be about,'' one aide says, ``but she will be getting talking points.''

No doubt Raisa Gorbacheva will be, too.