NEW YORK — No one under 21 would be able to buy cigarettes in New York City under a proposal unveiled Monday to make the city the most populous place in America to set the minimum age that high.
Extending a decade of moves to crack down on smoking in the nation’s largest city, the measure aims to stop young people from developing a habit that remains the leading preventable cause of death, City Council Speaker Christine Quinn said as she unveiled the plan. Eighty percent of the city’s smokers started lighting up before they were 21, officials say.
‘‘The point here is to really address where smoking begins,’’ she said, flanked by colleagues and the city’s health commissioner. With support in the council and Mayor Michael Bloomberg’s backing, the proposal has the political ingredients to pass.
But it may face questions about its effectiveness and fairness. A retailers’ representative suggested the measure would simply drive younger smokers to neighboring communities or corner-store cigarette sellers instead of city stores, while a smokers’ rights advocate called it ‘‘government paternalism at its worst.’’
Under federal law, no one under 18 can buy tobacco anywhere in the country. Four states and some localities have raised the age to 19, and at least two communities have agreed to raise it to 21.
In Massachusetts, the age limit is 21 in Needham and is headed toward 21 in Canton.
The Canton Board of Health agreed to the change this month, but it is not yet implemented, said John L. Ciccotelli, public health director. Plans call for an annual study of whether smoking declines among Canton high school students — and eliminating the measure in five years if it does not, he said.
In Needham, the high school smoking rate has dropped from about 13 percent to 5.5 percent since the 21-year-old threshold took effect in 2006, said Janice Berns, public health director.
It is not clear how much of the decline is due to the age limit.
A similar proposal has been floated in the Texas Legislature, but it is on hold after a budget board estimated it would cost the state more than $42 million in cigarette tax revenue over two years.
To public health and antismoking advocates, the cost to government is far outstripped by smoking’s toll on human lives.
They say a higher minimum age for buying tobacco discourages, or at least delays, young people from starting smoking and thereby limits their health risks.
‘‘Curtailing smoking among these age groups is critical to winning the fight against tobacco and reducing the deaths, disease, and health care costs it causes,’’ said Susan M. Liss, executive director of the Campaign for Tobacco-Free Kids.
Smoking has become less prevalent overall in New York City over the last decade but has plateaued at 8.5 percent among the city’s public high school students since 2007. An estimated 20,000 of them smoke.
It is already illegal for many of them to buy cigarettes, but raising the minimum age would also bar slightly older friends from buying for them.
City officials cited statistical modeling, published in the journal Health Policy, that estimated raising the tobacco purchase age to 21 nationally could cut the smoking rate by two-thirds among 14- to 17-year-olds and by half among 18- to 20-year-olds over 50 years. Texas budget officials projected a one-third reduction in tobacco product use by 18- to 20-year-olds.
A higher minimum tobacco purchase age could cut into sales that make up 40 percent of gross revenues for the average convenience store, said Jeff Lenard, a spokesman for the National Association of Convenience Stores.
But he suggested younger smokers might just go outside the city — the minimum age is 19 in nearby Long Island and New Jersey, for instance — or to black-market merchants.
To smoker Audrey Silk, people considered old enough to vote and serve in the military should be allowed to decide whether to use cigarettes.
‘‘Intolerance for anyone smoking is the antismokers’ excuse to reduce adults to the status of children,’’ said Silk, who founded a group that has sued the city over previous tobacco restrictions.
Advocates for the measure say the parallel is not voting but drinking. They cite laws against selling alcohol to anyone under 21.
The nation’s largest cigarette maker, Altria Group Inc., had no immediate comment, spokesman David Sutton said. He has previously noted that the Richmond, Va.-based company, which produces the top-selling Marlboro brand, supported federal legislation that in 2009 gave the Food and Drug Administration the power to regulate tobacco products, which includes various retail restrictions.
Representatives for R.J. Reynolds Tobacco Co. did not immediately respond to phone and e-mail inquiries. Based in Winston-Salem, N.C., it makes Camel and other brands.