Aboard thousands of airline flights the smoking lamp is about to be extinguished.

The federal ban on cigarette smoking on domestic flights of two hours or less about 80 percent of the total takes effect at 12:01 a.m. Saturday. Beforehand, some avid smokers are reconsidering train travel while others search for ways to keep their tobacco urges under control, at least for a few hours.Government and airline industry officials say they expect the new smoking restrictions to cause few problems, although some confusion may exist for the first few days.

"On the whole I think we're in reasonably good shape on this," said Transportation Secretary Jim Burnley, whose department issued the new restrictions earlier this month in compliance with a law enacted by Congress last year.

The Transportation Department and the Federal Aviation Administration have come under some criticism, however, for not pushing the airlines hard enough to publicize details of the new restrictions and avoid passenger confusion.

"The airlines do not have a uniform policy to inform the public" about the new rules, said Susan Bianchi-Sand, president of the 21,000-member Association of Flight Attendants.

She said at least one airline inserted details about the new requirements into flight crew manuals only this week, and four airlines are continuing to book seats in smoking sections of no-smoking flights.

The airlines said they hope a series of announcements to passengers both before and after boarding a flight will limit the confusion and perhaps head off any disturbances. Industry spokesmen noted that a smoking ban on flights within in California has been largely accepted since it went into effect at the first of the year.

An estimated 13,600 domestic flights a day will be affected by the no-smoking edict. International flights are not affected, and the length of a flight will be determined by the time shown in the airlines' official schedule.

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 has it as lasting two hours or less, FAA officials said.

The government has defined a flight as being any single segment between two cities. Thus, for example, a traveler flying from Washington, D.C., to Los Angeles with a stop in St. Louis would not be able to smoke on the first leg of the flight, but would be allowed to do so on the second, longer leg.

One major carrier, Northwest Airlines, is prohibiting smoking on all its flights within the continental United States, but so far no other airline has followed suit.

"We don't think our customers want us to become a non-smoking airline. If they tell us to do so, we will," Robert Crandall, chairman of American Airlines and himself a heavy smoker, said recently.

The battle over whether airline passengers should be allowed to smoke has been raging for nearly two decades, and forces on both sides of the issue say the fight is far from over despite the new restrictions.

Anti-smoking groups promise to push for a total ban on smoking aboard airliners, while the tobacco industry and many of its most loyal customers are gearing up to have the limited smoking prohibitions reversed in Congress.

The legislation enacted last year calls for the issue to be re-examined in two years.

"Believe me, we're working full speed ahead and so is the tobacco industry," says Ahron Leightman, president of Citizens Against Tobacco Smoke. "This is halftime in a football game. We're up 6-0, and during halftime the forces are regrouping."

"We remain very opposed to the two-hour ban," said Brennan Moran, a spokeswoman for the industry trade group, the Tobacco Institute.

Two-thirds of airline passengers favor a smoking ban on airlines, according to a study at the University of Missouri. Officials at Northwest Airlines said they instituted their ban on all flights after a survey showed only one in 10 passengers wanted to sit in the smoking section.