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.