He promised to obey the no-smoking rules in the White House, but whether that meant he would be ducking out the back door for a smoke is not known. His transition team declined to answer any questions about his smoking, past or present, or his efforts to quit.

Antismoking activists would love to see him use his bully pulpit to inspire others to join him in trying to kick the habit, but he has not yet taken up their cause.

The last president to smoke more than occasionally was Gerald R. Ford, who was quite fond of his pipes. Jimmy Carter and both Presidents George Bush were reportedly abstainers, but Bill Clinton liked cigars from time to time, though he may have chewed more than he smoked.

Mr. Obama’s heaviest smoking was seven or eight cigarettes a day, but three was more typical, according to an interview published in the November issue of Men’s Health magazine. In a letter given to reporters before the election, Mr. Obama’s doctor described his smoking history as “intermittent,” and said he had quit several times and was using Nicorette gum, a form of nicotine replacement, “with success.” Mr. Obama was often seen chewing gum during the campaign.

His pattern matches that of millions of other people who have resolved but stumbled in their efforts to give up cigarettes. Today, 21 percent of Americans smoke, down from 28 percent in 1988. Off-again-on-again smoking and serial quitting are common, as is the long-term use of nicotine gum and patches.

“It takes the average smoker 8 to 10 times before he is able to quit successfully,” said Dr. Steven A. Schroeder, director of the Smoking Cessation Leadership Center at the University of California, San Francisco.

Dr. Schroeder said that counseling was helpful, and that if Mr. Obama were his patient, he would urge him to try it, even if only by telephone, toll free at 1-800-QUITNOW (1-800-784-8669). With nicotine replacements and counseling, quit rates at one year are 15 percent to 30 percent, Dr. Schroeder said, about twice that of those who try without help.