DEAR READERS: Thursday marks the 14th annual Great American Smokeout, a one-day campaign to encourage smokers to quit smoking for 24 hours, just to prove they can do it.

Last year, more than 19.5 million smokers tried to quit for the day. This represents more than 39 percent of the nation's 50 million smokers. Breast cancer used to be the biggest killer for women. But the No. 1 cause of cancer death among women and men today is lung cancer. An estimated 142,000 will die of lung cancer in 1990.And now, a word about smoking-related diseases - emphysema, chronic bronchitis and heart disease: This year an estimated 390,000 will die from one of these. This total exceeds the number of U.S. battle deaths in World War II; it is nine times as many people who die in automobile accidents every year!

A congressional study has reported that health costs from the adverse effects of smoking have reached a new high of $100 billion per year in increased medical bills and lost productivity. The loss in death and disability cannot be measured. (And how does one measure the amount of heartache, remorse and guilt suffered as a result of a preventable, self-induced tragedy?)

What about "secondhand" smoke? Is it damaging to non-smokers to be in the presence of those who are smoking? Yes! Furthermore, studies reveal that the children of smokers are more prone to lung problems and allergies than are children of non-smokers.

For years I have begged my young readers, "If you smoke, quit now. If you don't smoke, don't start!" Yet an estimated 3,000 to 5,000 kids light up for the first time every day. Why? Peer pressure, no doubt.

Quitting "cold turkey" is the hardest way to quit, but my readers have told me it's the most effective, and in the long run, the easiest way. Cutting down is less traumatic, but the temptation to smoke is often too powerful to resist while smoking just one, two or three cigarettes a day.

Those who are heavily addicted may require help to break the habit. Call your local chapter of the American Cancer Society for information.

So if you're hooked on cigarettes and have been telling yourself, "One of these days I'm going to quit," why not start Thursday?

It won't be easy, but it will be the best Thanksgiving present you can give yourself - and those who love you. - LOVE, ABBY

P.S. A favor, please? If you quit, even for 24 hours, I want to hear from you. Then write again and let me know how long you were able to stay "clean." Good luck. Keep me posted. I care.

DEAR ABBY: My husband and I received a good chuckle from the letter in your column about the two less-than-perfect junco birds who fell in love. We have been married for 23 years. I am not sure if the results of our childhood traumas had anything to do with our meeting and falling in love, but he's blind in one eye and I wear an artificial right leg. - DEE MALCHOW IN SEATTLE

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, IL 61054. (Postage is included.)