Two New Jersey lawmakers proposed Thursday to raise their state’s minimum age for buying cigarettes to 21, reaching across the Hudson River to borrow an idea from New York City in a gesture of regional cooperation to keep tobacco from many young adults.

In the unusual move that highlighted a spirit of alliance between sometime rivals, New Jersey state Sen. Richard Codey and Assemblyman Ruben Ramos unveiled the proposal at New York’s City Hall.

“I think we have to send a message to our young adults: to smoke is no joke,” Codey said. As acting governor, he signed a measure raising the age limit from 18 to 19 seven years ago.

Earlier this month, Egg Harbor City restricted smoking in most park and public areas.

The Atlantic Prevention Resources of Pleasantville reports the seven southernmost counties in New Jersey have an average smoking rate of 20 percent, compared with 14 percent statewide.

The group’s executive director, Bob Zlotnick, said increasing the age limit could stop some from smoking at an earlier age.

“Young people, including young adults, sometimes don’t make the best decision,” he said. “We have seen that time and time again.”

But Zlotnick noted that most young smokers begin well before age 21, and that at that young age, their brains and bodies are not fully formed, which is why smoking is such a danger.

Ocean City High School teacher Tom Gahr, founder of the school’s Student Coalition Against Tobacco, said increasing the age limit would serve as a deterrent for kids to start smoking and would send a message the state is looking out for the health of its residents.

“If someone can get to age 21 without smoking a cigarette, it is very likely they will produce one of the healthiest choices you can make, which is live a tobacco-free life,” he said.

Sen. Jeff Van Drew, D-Atlantic, Cape May, Cumberland, said he does not want anyone to smoke, but wrestles with taking away the right for these young residents to make a decision.

“We allow young men and women to make a decision to lose their life and protect their country at age 18,” he said. “I think it’s a bad thing. I don’t want them to have a cigarette. But if they have the freedom to do one thing, they should have the freedom to do the other.”

While the threshold already has been raised to 21 in two Boston suburbs, the idea has gained more attention since New York City Council Speaker Christine Quinn and colleagues proposed it in the nation’s biggest city last month. Some state lawmakers have since proposed doing likewise throughout New York. The minimum age now is 18 in the city and state, although some New York counties have boosted it to 19.

Under federal law, no one under 18 can buy tobacco anywhere in the country.

Advocates say higher age limits help stop, or at least delay, young people from developing a habit that remains the leading cause of preventable deaths in the U.S., despite decades of efforts to call attention to its dangers. The measures make it tougher for 18- to 20-year-olds to obtain cigarettes for themselves and for younger friends, supporters say.

Altria Group Inc., which produces the top-selling Marlboro brand, suggested the proposal would “restrict adult consumers’ access to legal products,” while noting that it hadn’t seen details.

“We have encouraged state and local governments, along with our retail customers, to vigorously enforce existing minimum age requirements,” and Richmond, Va.-based Altria supported setting the federal minimum age at 18, spokesman David Sutton said in a statement.

A representative for R.J. Reynolds Tobacco Co., maker of brands including Camel, didn’t respond to phone and email inquiries.

Higher age limits have faced criticism from smokers’ rights advocates who feel the restrictions are unfair and patronizing to an age group considered old enough to make such adult decisions as voting and serving in the military. Manufacturers and some retailers have suggested young adult smokers may just turn to black-market merchants or to nearby areas with lower age limits.

The New York and New Jersey advocates say that’s a good reason to set the limit at 21 regionwide.

New Jersey raised the limit to 19 in 2006, in tandem with a considerably more controversial measure that outlawed smoking in bars, restaurants and most other indoor public places. Codey and Ramos said they planned to introduce the 21-year-old limit formally Monday in the state Legislature.

The measure is progressing in New York’s City Council, with a vote likely sometime this summer. Mayor Michael Bloomberg, who had opposed higher age limits in the past, supports the current plan.

Staff Writer Joel Landau contributed to this story.