Boston ? A national survey has found that workers in many parts of the country are growing more unhappy with their jobs and nowhere more so than New England.

Only 51 percent of the 5,000 people surveyed said they were satisfied with their jobs, compared with 59 percent in 1995. The mail survey was conducted in March by the New York-based Conference Board, which did not provide a margin of error.

The survey suggested most Americans find their jobs interesting and are even satisfied with their commutes. But the survey said only one worker in five was satisfied with their companies’ promotion policy and bonus plans, while nearly two in five were content with their wages.

Job satisfaction in the northern Midwest, Prairie and south central states Kentucky, Tennessee, Alabama and Mississippi has dropped below 50 percent since 1995. But it was lowest in New England at only 44 percent, compared with 56 percent in 2000 and 65 percent in seven years ago.

“I’m personally happier but I observe more people that are more miserable,” said Marc Greenbaum, 50, a professor at Suffolk Law School. “There’s more pressure on them to produce, more problems with maintaining a boundary between work and family, even maintaining a boundary between work and the outside because of things like e-mail, voicemail and the Blackberry. They can’t get away.”

Job satisfaction was highest in Rocky Mountain states, though the percentage dropped from 63 percent in 1995 to 57 percent this year.

Lauren Trout, 23, a bicycle messenger in Denver, said she could always do with a higher salary. “But otherwise, as far as the work goes, I like it. I’m pretty happy with it,” she said.

The survey found that job satisfaction increased with income levels, but even among higher-earning households it dropped from 67 percent in 1995 to 55 percent in 2000 and again this year.

Less than 48 percent of people aged 35 to 44 were satisfied with their work, compared with nearly 61 percent in 1995. The most satisfied age groups were those under 25 and over 65.

George Walker, 66, who lives and works in Denver, said he was happy with his salary but wished some things at work could change.

“I’d like to be more active,” he said. “I’d like to have more say. I’d like to feel like I had more power. I’d like to feel like I was more in control.”