The age to legally buy cigarettes in New York City would rise to 21 from 18 under a proposal that officials unveiled on Monday, a measure that would give New York the strictest limits of any major American city.

The proposal would make the age for buying cigarettes and other tobacco products the same as for purchasing liquor, but it would not prohibit people under 21 from possessing or even smoking cigarettes.

It is the latest effort in a persistent campaign to curb smoking that began soon after Mayor Michael R. Bloomberg took office, with bans on smoking in restaurants and bars that expanded more recently to parks, beaches, plazas and other public places.

But this latest proposal, announced by Dr. Thomas A. Farley, the city’s health commissioner, and Christine C. Quinn, the City Council speaker and a mayoral candidate, puts New York squarely into the middle of a debate over the rights and responsibilities of young people, and it drew much skepticism. At 18, New Yorkers are old enough to fight in wars, to drive and to vote, but if the smoking restriction passed they would be prohibited from deciding whether to take the risk of smoking.

Ms. Quinn and Dr. Farley defended the proposal, saying that people typically make the transition from experimental smoking to regular smoking around age 20, and that by making cigarettes harder to obtain at a young age the city would make it less likely that people would become lifelong addicts.

“With this legislation, we’ll be targeting the age group at which the overwhelming majority of smokers start,” Ms. Quinn said in announcing the legislation at a City Hall news conference.

While officials focused on the public health aspect of the age limitation, the announcement was also infused with political overtones. In the past, Mr. Bloomberg had always been on hand, standing in front of television cameras to boldly promote public health initiatives. But on Monday he was nowhere to be seen, allowing Dr. Farley to represent the administration and seemingly ceding the spotlight to Ms. Quinn, who initiated the proposal.

By proposing the legislation, Ms. Quinn, a Democrat who polls show is a leading candidate to succeed Mr. Bloomberg, appeared to be positioning herself to follow in his footsteps as a mayor who would make public health a top priority.

Mr. Bloomberg, in fact, had opposed a similar measure in 2006, arguing that raising the age to buy cigarettes would actually make smoking more enticing to teenagers. But he now believes differently, a spokeswoman said, because the city’s youth smoking rate has plateaued and recent research has suggested a correlation between a higher smoking age and lower smoking rates.

In interviews, many New Yorkers were largely critical of the proposal, viewing it as an attack on the maturity and self-determination of young people.

“By 18, people are responsible enough to make their own decisions,” said Erik Malave, 23, a music production student at City College. “Forcing people to make themselves healthy tends not to work.”

Mr. Malave, from Yonkers, has been smoking for about three years, and he breaks for a cigarette four or five times a day. He also said that he thought the law would be a waste of time, and that young people would easily acquire cigarettes if they wanted them. “When I turned 18, I bought cigarettes for all my friends who weren’t 18,” he said.

Jessette Bautista, 21, began smoking when she was 17 and had no problem getting cigarettes from friends who would buy packs for her. She was surprised to hear about a proposal to change the legal age to purchase cigarettes. “What happened to freedom?” she said.

While alcohol may impair a person’s judgment and so warrants a law that requires partakers to be 21 or older, Ms. Bautista said, cigarettes do not alter a person’s state of mind. “Cigarettes will not intoxicate you the same way as alcohol,” she said. “It will not put you under any influence.”

Under the proposal, the buyer would not be violating the law, but the seller would be. Fines and other penalties for selling cigarettes to minors would remain as they are now and would be imposed on the sellers, not the buyers or their parents.

Asked whether the proposal would infantilize young people, Ms. Quinn said that age 21 “seems to me to track very much with a point we have marked in society” about when people are capable of making decisions about certain potentially risky behaviors like drinking.

She said there was “clear data” that 80 percent of smokers started before age 21, adding, “We have an ability to intervene on that and make a difference.”

Dr. Farley lamented that after 10 years of decline, the youth smoking rate in the city had stalled at 8.5 percent in 2007, with 20,000 public high school students currently smoking. The rate of smoking among adults has declined from 21.5 percent in 2002 to 14.8 percent in 2011, a 31 percent decrease. In the past, city officials have suggested that public education campaigns have been effective in persuading many young people never to start smoking.

The Council is considering a Bloomberg proposal to require retailers to keep tobacco products where customers cannot see them, which the mayor said would shield children from tobacco marketing and keep people from buying cigarettes on impulse.

In pushing their latest antismoking initiative, city officials cited a 2010 study in England showing that smoking among 16- to 17-year-olds dropped by 30 percent after the legal age of sale for cigarettes was raised to 18 from 16 in 2007.

The New York proposal has to be approved by the Council and signed by the mayor, but its enactment is likely since it is being promoted by Ms. Quinn and is supported by Mr. Bloomberg.

The smoking age is 18 in most of the country, but some states have made it 19. Some counties have also adopted 19, including Nassau and Suffolk on Long Island. Needham, Mass., a suburb of Boston, raised the smoking age to 21 in 2005.

California and Texas have been at the forefront of the fight to raise the tobacco sale age to 21, but have been stymied by fears of lost tax revenue. Ms. Quinn argued that health care savings would more than make up for any potential tax revenue losses.

New York officials estimated that raising the age to 21 would reduce the smoking rate among 18- to 20-year-olds by 55 percent, and by two-thirds among 14- to 17-year-olds.

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By ANEMONA HARTOCOLLIS