AUGUSTA, Maine — Maine today joins other states and Canadian provinces that have made it illegal to smoke in a car while children are present. But for the first year the law is in effect, violators will only get warnings.

A law passed by the Legislature earlier this year outlaws smoking in cars while youths under 16 are present. It’s modeled after a tougher Bangor ordinance. California, Arkansas and Louisiana have passed similar laws, as have Puerto Rico and some Canadian provinces. Other states have also looked at the proposal.

When he signed Maine’s bill into law in April, Gov. John Baldacci hailed the legislation as a strike against secondhand smoke, saying that tobacco use costs too many lives and too much money.

The federal Environmental Protection Agency, which urges smoke-free homes and cars, says secondhand smoke increases the number of asthma attacks and severity of asthma symptoms as well as lower respiratory tract infections for children under 18 months of age.

Developing lungs of young children are severely affected by exposure to secondhand smoke, the EPA says. Children receiving high doses of secondhand smoke, such as those with smoking mothers, run the greatest risk of damaging health effects. The U.S. Surgeon General also warns of links between secondhand smoke exposure and cancer and heart disease.

While opponents of the Maine law raised concerns it would infringe on people’s private liberties, its chief sponsor said he has seen firsthand the positive effect of such a law.

Rep. Brian Duprey, R-Hampden, said he ordinarily would oppose legislation he sees as government interference in people’s privacy.

But Duprey, who runs a child care business, said he was moved to act after seeing tots arrive at his facilities smelling of tobacco and often sick. After neighboring Bangor became the state’s first city to adopt an ordinance to outlaw smoking in cars with children, Duprey said, the children smelled better and the rate of illnesses dropped sharply.

Maine’s law authorizes police to hand out only warnings until Sept. 1, 2009, but after that violators can get $50 fines.

California’s law, by comparison, authorizes fines of up to $100, while Ontario violators face $250 fines. Another Canadian province, British Columbia, also followed Nova Scotia’s example in passing such a law. Some Australian states also ban smoking in cars where children are present.