NEW YORK, FEB. 14 -- Railroad commuters who smoke will have to go cold turkey to and from work under a smoking ban that takes effect Monday on all Long Island Rail Road and Metro-North Commuter Railroad trains.

The rail lines' parent agency, the Metropolitan Transportation Authority, approved the ban Jan. 22 after Congress threatened to cut off $539 million a year in federal funds if smoking continued.

Although Metro-North, which serves Westchester County and Connecticut, would not have been affected by the cut, MTA board members voted to ban smoking on all trains to have a uniform, systemwide policy.

Union leaders and MTA Chairman Robert Kiley, a reformed three-pack-a-day smoker, endorsed the smoking ban. Smokers who light up can be fined $100.

"We will try not to give out summonses, but we expect our passengers to obey the law," said Brian Dolan, a LIRR spokesman.

Because Monday is the Presidents' Day holiday, the impact of the ban is not expected to be felt until Tuesday, when smokers returning to work will be expected to pocket their tobacco products during the commute.

"The big to-do will be Tuesday," said Dan Bruckner, spokesman for Metro-North. "We're trying to prepare ourselves for that."

One Metro-North smokers' group, Commuters for Fair Treatment, filed suit last week in state Supreme Court, charging that the MTA imposed the ban without adequate time for public comment. Justice Alvin Rufkin refused to block the ban but ordered both sides to submit additional written arguments by Feb. 25. Philip Morris Inc. tobacco company is funding the suit.

Bruce McIver, president of the LIRR, estimated that the ban would save the railroad $600,000 a year in maintenance costs and salaries.