By repeatedly putting their nicotine urges on hold for manageable periods, smokers gain practice and self-confidence for after they quit altogether, Dr. Cinciripini said.

The researchers studied two versions of the clock strategy. The better result came from forcing smokers to gradually reduce the number of cigarettes smoked, rather than maintaining their normal level of consumption before quitting.

In the study of 128 smokers, the clock strategy was part of a nine-week program that also taught how to resist the urge to smoke.

First, researchers took the number of cigarettes each smoker consumed per day and scheduled smoking to occur at regular intervals. A person who usually smoked 30 cigarettes a day and stayed awake for 15 hours, for example, got smoking times that allowed one cigarette every half-hour. Smokers had to light up within five minutes of the scheduled time. If they missed it, they could not make it up later.

The next week, their schedule was adjusted to allow one-third fewer cigarettes. The week after that brought another one-third cut. And the week after that, the consumption was reduced again to an average of three or four cigarettes a day. Then came the target date for quitting.

Smokers who used that strategy showed a 44 percent success rate one year after the smoking program ended.