Undated (AP) _ It's butts out for about 80 percent of all domestic flights today, but airlines and experts have some healthy advice for inveterate smokers climbing the cabin walls: Take deep breaths, chew gum and snap a rubber band.

The federal ban on smoking on domestic flights of less than two hours went into effect at 12:01 a.m. EDT today.

''I'll just have to smoke like a fiend until I get on,'' said Linda Navarro of Fullerton, Calif., as she prepared to board a flight at Los Angeles International Airport.

The regulation carries more than a wrist slap for violators: a fine of up to $1,000 for smoking and $2,000 for tampering with aircraft lavatory smoke alarms.

Those who disobey a flight attendant's order to put out a cigarette could land in jail. Airlines say they may ask police to meet the plane at its next destination, or even divert the aircraft in cases involving unruly smokers.

''The majority of us absolutely support the new law,'' USAir flight attendant Suzanne Haughton told the Los Angeles Times. ''I don't look forward to the conflicts that will come with it, though. There are going to be problems. There are passengers who rip your head off on a 28-minute flight if they can't smoke.''

''I'm thrilled. I'm so happy. I just can't breathe anymore on these flights,'' United Airlines flight attendant Terry Cale said in San Francisco. ''I'm afraid to go to the doctor to have my lungs examined for fear of what they'll find.''

Not everyone was as thrilled. ''Flying is already stressful enough, and now they're going to make it worse if they won't let me smoke up there,'' said Lother Straschnitzki of Sonoma, Calif., waiting for his flight to be called at San Francisco International Airport. ''It's going to bother me a lot.''

''I survived,'' said Tom Brand of Fort Lauderdale, Fla., who lit up the minute he stepped off his Delta flight from Fort Lauderdale to Atlanta.

But the hopelessly hooked needn't despair. The airlines plan to offer substitutes for cigarettes, including hard candy and a chewing gum designed to lessen withdrawal symptoms.

Dr. Don R. Powell, executive director of the American Institute for Preventive Medicine, advises putting a rubber band around the wrist of your smoking hand and snapping it whenever a nicotine urge strikes.

''Our employees have been briefed,'' said Paula Musto, a spokeswoman for Eastern Airlines. ''The flight attendants, as the front-line people, will have to deal with it more than anybody.''

Under the new rules, airlines are required to announce before takeoff that smoking is prohibited, and to keep ''No Smoking'' lights illuminated.

Even if a flight is delayed in the air or on the ground and goes beyond two hours, smoking will be prohibited if the schedule lists it as lasting two hours or less, according to the Federal Aviation Administration.

American Airlines is providing cinnamon hard candies to smokers, suggested by the American Heart Association and the American Lung Association as a cigarette substitute. Continental Airlines is distributing more than 430,000 pieces of a gum called ''Ban Smoke,'' formulated to temporarily control the urge.

Northwest Airlines, whose anti-smoking policy goes beyond the federal requirement by banning smoking on nearly all domestic flights, is handing out candies and mints as well as brochures.

From United Airlines, here are some suggestions from medical director Dr. Gary Kohn:

-If you usually smoke while sipping coffee, soft drinks or alcohol during flights, try switching to fruit juices, water or milk.

-Strike up a conversation with a fellow passenger instead of striking a match. Write letters or a business memo.

-Practice deep breathing.

-Read a book or a magazine.

The American Institute for Preventive Medicine, based in Southfield, Mich., has also developed a kit, called ''Flying Smokeless,'' that contains a cassette tape of behavior modification techniques and a ''smokeless emergency pack'' containing gum, mints and toothpicks. It sells for $11.45.

The Great American Smokers Club, a charter service that was to begin service Friday from Dallas and permit smoking in all seats, has been forced to postpone service because of complications with federal regulations, company executives said.