My 14-year-old son, "Adam," has known he was adopted since he was old enough to understand. Adam's birth parents both were addicted to drugs, alcohol and tobacco. In fact, Adam tested positive for cocaine at birth.

Should I tell him that he is at risk for addiction because of his biological heritage? I want him to be aware, yet I don't want to bad-mouth his birth parents or in any way lead him to think that this is his destiny. I know he associates with kids who may be involved in these things.

- Concerned Mom in Atlanta

DEAR CONCERNED MOM: Frankly, you should have had this conversation with Adam by the time he was 9. He must definitely be given this information. To remain silent would be like failing to warn a child with balance problems not to walk a tightrope.

It would not be "bad-mouthing" to explain to Adam that because his adoption records show his parents were both addicts, it's extremely important that he avoid addictive substances because he could become addicted more easily than the average person. Explain that while it isn't a guarantee that he'll become hooked, the tendency is there. Forewarned is forearmed.

DEAR ABBY: I am one of your male readers. A year and a half ago, my brother was killed in an automobile accident by a drunken driver. We are a very close family, and everyone was devastated. My sister-in-law, "Grace," and I were always close, and we have become closer lately. Now we're discussing the possibility of a relationship.

Grace has three grown sons, and I realize there could be issues or concerns with the boys and our families, but we feel they would want us to be happy.

Is this something that is acceptable, and does it happen often? We have never discussed the fact that I am not my brother and cannot - and never would try to - replace him. I couldn't. He was a great man.

- Looking for Insight in the Midwest

DEAR LOOKING FOR INSIGHT: While I do not have any statistics about widows and widowers becoming romantically involved with former in-laws, I can tell you that this situation is not as unusual as you might think, and the subject has appeared before in my column. It is understandable that you and Grace would be drawn to each other. You have years of shared history in common, and that could form the basis of a very successful union. If you love each other, I say go for it.

DEAR ABBY: When I take a break at work I like to read, but I am often interrupted by co-workers. Even though they see me reading, they insist on starting a conversation. I don't mean to be rude, but it is relaxing for me to "escape" for a few minutes, and I feel robbed when I can't enjoy my latest book. It is too far to go to my car, and we are not supposed to leave the area anyway.

What can I do or say without being considered unkind?

- Anita in Cincinnati

DEAR ANITA: Try this - nicely warn your co-workers in advance that reading is your form of relaxation and you would appreciate it if they let you concentrate on your book during your break. That way, everyone will get the message in a nonconfrontational way.

Another thought: Place a Do Not Disturb sign with large lettering next to you if you think it will help them get the hint. *

What teens need to know about sex, drugs, AIDS and getting along with peers and parents is in "What Every Teen Should Know." To order, send a business-sized, self- addressed envelope, plus check or money order for $6 (U.S. funds) to: Dear Abby - Teen Booklet, P.O. Box 447, Mount Morris, IL 61054-0447. (Postage is included in the price.)