There's never been a better time to quit smoking. Not only do smokers have a growing arsenal of weapons to extinguish their cigarette craving, but tomorrow they will get nationwide moral support during the Great American Smokeout.

An estimated one in five smokers -- some 11 million Americans -- are expected to go 24 hours without taking a puff in observance of the nation's eighth annual smoke-free day, sponsored by the American Cancer Society. Last year, 1.8 million smokers used their cigarette-shunning experience as a springboard to quit and still were not smoking six months later, the cancer society reports.

Numerous organizations throughout the area will sponsor smokeout efforts tomorrow as the nation moves towards a goal set by U.S. Surgeon General C. Everett Koop for a smoke-free society by the year 2000. At Howard University, students will receive extra credit for "adopting" smokers and helping them stop. The Department of Education, the Library of Congress and Group Health Inc. will hold free smoking cessation clinics for employes. Columbia Hospital for Women will serve a continental breakfast to help staffers keep from lighting up, and D.C. General Hospital will offer coffee mugs to employes who quit smoking for the day.

There have never been more reasons to kick the habit. Since the 1964 U.S. Surgeon General's report first warned of the link between cigarette smoking and lung cancer, "some 30,000 scientific papers have been published relating smoking to serious disease," writes Judith Ockene in this month's American Journal of Public Health. Besides the well-known connection to respiratory illnesses, smoking is related to an increased rate of heart disease, digestive problems, early onset of menopause and development of intermittent claudication -- a painful circulatory disease that gradually narrows blood vessels in the legs and limits movement.

Last week, a study published in the New England Journal of Medicine added cardiomyopathy -- a fatal heart condition -- to the list of smoking-related illnesses. Heavy smokers have almost three times the risk of developing the disease -- which claims some 10,000 lives a year -- reported researchers from the Medical College of Wisconsin. The only known cure is a heart transplant.

If the consequences of smoking have never seemed grimmer, the aids for quitting has never been more plentiful.

Today, smokers can chew their way to cessation with Nicorette -- a nicotine-containing chewing gum available by prescription. Recent research offers smokers a strategy to avoid the weight gain often associated with quitting. Added pounds are related to a quitter's increased desire for sweets -- not to overeating in general -- report studies by researcher Neil Grunberg of the Uniformed Services University of Health Sciences. Substituting reduced calorie sweeteners or cutting out sweets altogether should help ex-smokers avoid weight gain.

New research also suggests that Clonidine, a prescription drug used for treating high blood pressure, is effective in controlling the "craving and acute withdrawal of cigarette smoking on a short-term basis," reports Dr. Alexander Glassman in this week's Science magazine. Whether Clonidine will be helpful in long-term smoking abstinence "is not yet known," says Glassman, a researcher at the New York State Psychiatric Institute. "But the drug is potentially a very useful tool."

Smokers who want to quit can also turn to free or low-cost materials and programs offered by local chapters of the American Cancer Society (232-3309), the American Heart Association (337-6400) and the American Lung Association (682-5864).

Smokeout activities include:

"Breathing Easy," a one-hour television special explaining the physical effects of smoking and exploring the subliminal messages contained in cigarette advertising. Tonight at 9 on Channels 26 and 32.

Distribution of survival kits, candy and raisins today by the American Cancer Society and tomorrow at trading booths throughout the metropolitan area. Call 232-3309.

Hotlines for moral support, open from 9 a.m. to 9 p.m. tomorrow. In the District and Maryland, call 483-2600. In Virginia, call toll-free, 1-800-552-7996. The nationwide hotline offers a taped message for 50 cents a call: 1-900-210-KWIT.

"Searching for a Way Out," a new, free pamphlet of quitting techniques. Send a stamped (37 cents postage), self-addressed business-size envelope to Smoking Cessation Booklet, American Council on Science and Health, 47 Maple St., Summit, N.J. 07901.