NEW YORK (Reuters) - Poor smokers in New York State spend about a quarter of their entire income on cigarettes, nearly twice as much as the national average for low-income smokers, according to a new study.

The study, conducted by the non-profit research group RTI on behalf of the state's health department, found there was no statistically significant decline in the prevalence of smoking among poorer New Yorkers between 2003 and 2010, even as the habit declined by about 20 percent among all income groups.

"Although high cigarette taxes are an effective method for reducing cigarette smoking, they can impose a significant financial burden on low-income smokers," Matthew Farrelly and his co-authors wrote in the conclusion of their paper, which was published this month in Plos One, an online, peer-reviewed journal.

Using data from the state health department's New York Adult Tobacco Survey, researchers calculated that smokers in New York earning less than $30,000 a year spent an average of 23.6 percent of their earnings on cigarettes, compared with about 14.2 percent nationally.

The state's wealthier smokers - those earning over $60,000 - spent an average of 2.2 percent of their income on the habit, about the same as the national figure.

New York has the highest state cigarette tax in the nation, at $4.35 a carton, compared with a national average of $1.46. New York City imposes an additional $1.50 tax. The researchers said they did not have enough data to measure whether city residents were shelling out an even larger portion of their earnings on cigarettes.

The low-income now spend twice as much of their earnings on cigarettes as they did in 2003, when the state imposed a tax of $1.50 on each carton.

The researchers concluded that to make the cigarette tax less regressive, the state should spend more of the resulting revenue on programs that help low-income smokers quit the habit, although both the researchers and the health department say this would be a challenge.

"They can be a hard-to-reach population," Peter Constantakes, a health department spokesman, said in an interview on Wednesday.

Raising the cost of cigarettes through taxation is a proven method of encouraging smokers to quit, he said.

The state spends about $41 million a year on tobacco control programs - about half of what it spent four years ago.

(Editing by Paul Thomasch and Leslie Adler)