DEAR ABBY: This is a belated thank-you letter for something you printed in your column several years ago.

I lost my father suddenly last year. As difficult as his death was, I had peace of mind knowing that I had left nothing unsaid. Because of a Father's Day column you wrote, I sent my father a three-page letter instead of a necktie. It was a difficult letter to write because I had never verbalized my feelings about him, but once I started to tell him how important he had been in my life, and how much I owed him for raising me to be a caring, responsible, productive person, it was easy.

I will never forget the expression on his face as he read my letter. When he finished, he told me that he had never before received such a precious gift.

My father died knowing how much I loved and appreciated him. Abby, please make that suggestion to your readers every year. Thank you from the bottom of my heart. -- JUDY THRASHER, DEFIANCE, OHIO

DEAR JUDY: Here's your letter, dedicated to the memory of your beloved father. And thank you, Judy, for giving me permission to use your name when I telephoned you.

DEAR ABBY: Unfortunately, your advice to "Anonymous in the USA," the working couple who had never filed income tax returns, fell short of the best advice they should have received.

Contacting the IRS in this situation without first seeking the professional advice of a qualified, experienced CPA or tax attorney is asking for more, not less, trouble. While it's possible that they might emerge unharmed, the risk of far harsher treatment is too high.

Much better for them to consult with an experienced tax accountant or attorney so they can learn their rights as well as their obligations. So much of this couple's financial and emotional future is at stake; they need expert outside advice on this kind of problem, Abby.

In the past, you have advised people who have legal problems to seek legal advice; this situation is no different. Please correct your advice to this couple before too many people follow it. -- DONALD B. WALTER, CPA, SEATTLE

DEAR MR. WALTER: I just did, thanks to you.

DEAR ABBY: Was it you who wrote:

"Women in slacks

"Should not turn their backs"?

-- HARRY IN MANITOWOC, WIS.

DEAR HARRY: No, but thanks for the compliment. The author was Ogden Nash, who must have been fixated on ladies' derrieres because he also wrote:

"Deck your lower limbs in pants, my sweet.

"You have seen yourself advance,

"But have you seen yourself retreat?"

Everything you'll need to know about planning a wedding can be found in Abby's booklet, "How to Have a Lovely Wedding." To order, send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Wedding Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)

DEAR ABBY: I have just been informed of a very delicate situation, and I am not sure how to handle it. My husband and I separated for a short time in September 1988. While separated, I started seeing another man. It was a very brief encounter, needless to say. Since then, my husband and I are together again -- and I have given birth to a son.

I recently ran into some friends who knew of this other man and also live near him. My friend told me some very disturbing news about this man. He has been diagnosed HIV-positive. Needless to say, I was floored hearing this. I plan to be tested very soon.

The problem is: Should I discuss this with my husband? If I tell him, it could destroy what is left of our marriage, especially if the test is negative. On the other hand, he has a right to know that the risk is there.

I cannot even comprehend the fact of AIDS. The thing that gets to me more than anything is my son. I had him after the fact. Is he infected? I could not live with myself knowing that my lack of self-control could possibly kill both of us. Please help me any way you can. -- DEVASTATED

DEAR DEVASTATED: You must be tested immediately to determine whether you have been infected, and have your questions answered first-hand. Call the government AIDS hotline: 1 (800) 342-AIDS to find the location of a center near you for anonymous testing. If you are positive, then you must discuss this with your husband, and both your husband and your child should be tested.

If you are negative -- it's "our" secret.

DEAR ABBY: I am a 15-year-old high school sophomore and my parents have this rule: I cannot go in cars driven by any of my friends. Abby, they have driver's licenses and are all good drivers, but my folks won't listen. I hope to get my own driver's license when I turn 16. I'm taking Driver's Education in school.

I have been asked on dates by guys my age, but of course I can't go because of this dumb rule my parents are sticking to. Abby, it's very embarrassing to be driven places by my parents.

Why do parents worry so much? It's like they don't ever want their kids to grow up. -- FOREVER A BABY

DEAR FOREVER: Why do parents worry so much? Because it's every parent's nightmare that their teen-ager will be badly hurt -- or killed -- in an automobile accident.

If your friends who drive would meet your parents and impress them with their maturity and sense of responsibility, it may make a big difference in your parents' attitude. It's worth a try.

DEAR ABBY: I do something I think more people would do if they just stopped for a moment and thought about it.

I have a very select list of charities I always give to. But when I send a check, I also include a short note: "Please do not send me a thank-you! Save the postage. My canceled check is my receipt." -- DON C. IN K.C., MO.

DEAR DON: Thanks. I learned something today. Most charities need every penny they can raise.

To get Abby's booklet "How to Write Letters for All Occasions," send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Letter Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)

DEAR ABBY: When we bought our home up north 30 years ago, this motto was tacked to the frame of the entrance. We thought it was appropriate then, and still is now.

I thought you might want to share it with your readers. -- A.M.T. IN FLORIDA

GO TO WORK AND SAVE $$

If you are poor -- work.

If you are rich -- continue to work.

If you are happy -- keep right on working.

Idleness gives you room for doubts and fears.

If disappointments come -- work.

If sorrow overwhelms you, and loved ones seem not true -- work.

When faith falters and reason fails -- just work.

When dreams are shattered and hope seems dead -- work.

Work as if your life was in peril. It really is.

Whatever happens or matters -- work.

Work faithfully -- work with faith.

Work is the greatest material remedy available.

Work will cure both mental and physical afflictions.

-- From the "Silent Partner"

DEAR A.M.T.: Thanks for a worthwhile addition to this space. But how about all those people who are willing and eager to work, but cannot find a job?

DEAR ABBY: This letter is for all of those frustrated housewives who wonder if they've gone off their rockers when they find only one sock in the washing machine. You dealt with this problem some time ago by stating that washers and dryers do not eat socks.

Sorry, Abby, but the washer is, in fact, the culprit. I have worked in customer service for General Electric Major Home Appliance Repairs for many years, and we were instructed to tell our customers that the washing action of the water will sometimes push a lighter item, i.e. a sock or washcloth, over the top of the inner tub into the space between the inner and outer tub -- and during the pumping cycle it can be washed down the sewer.

I have scheduled hundreds of service calls for socks to be removed from the pump of a washing machine. So, women, take heart, and tell your husbands to go yell at the washer! -- NEW ORLEANS WOMAN

DEAR NEW ORLEANS WOMAN: I'm sure that many who have thought they were going crazy after discovering an odd number of socks in their washing machines will appreciate your explanation. Here's suds in your eye!

DEAR ABBY: My husband thinks I'm some kind of cleanliness nut because I shower every night before going to bed. I believe it's just good personal hygiene. Please comment. -- SHOWER FREAK (HIS NAME FOR ME)

DEAR SHOWER FREAK: I'm with you. Cleanliness is next to godliness.

Everything you'll need to know about planning a wedding can be found in Abby's booklet, "How to Have a Lovely Wedding." To order, send a long, business-size, self-addressed envelope, plus check or money order for $3.95 ($4.50 in Canada) to: Dear Abby, Wedding Booklet, P.O. Box 447, Mount Morris, Ill. 61054. (Postage is included.)