NEW HAVEN, Conn. – New England stands to lose about 20 percent of its congressional seats over the next quarter-century as political power follows population booms in the South and West, newly released census data show.

Population projections released Thursday by the U.S. Census Bureau project much slower growth in New England. They also paint a picture of a region that is increasingly elderly, especially in Vermont, New Hampshire and Maine, where statisticians expect a dramatic spike in the number of residents older than 65.

If the projections hold true, Massachusetts would lose two of its 10 congressional seats, Connecticut would lose one of its five and Rhode Island would lose one of its two, according to an Associated Press analysis of the data.

That diminished political clout threatens to make it harder for New England lawmakers to push regional issues such as transportation and home heating costs onto the national agenda.

The states also will have to grapple with how to afford the costly social services required by their aging population. Experts say lawmakers won’t be able to rely on Washington to fund those programs, as states around the country jockey for money to deal with aging baby boomers.

By 2030, the Census Bureau projects that 26.5 percent of people living in Maine will be over 65, a percentage that would trail only Florida’s projected 27.1 percent.

“That means more concerns about budget pressures for health care, more concerns over rising housing costs when it’s already getting difficult to add to the supply,” said Jeffrey Carr, the state economic forecaster in Vermont, which is projected to see a 149 percent increase in the number of residents over 85 years old. “There’s a million ramifications to this.”

The federal government allocates seats in the House of Representatives every 10 years based on census data. Massachusetts lost a seat in 1980 and another in 1990, and Connecticut lost one in 2000.

In 2030, according to census estimates, New England will have about 15.6 million residents, up about 12 percent from 2000. That compares to 51 percent growth projected in the South Atlantic states and 65 percent growth projected in the Mountain region.

“New England is on the edge of a precipice here because of the political shifts dictated by population growth,” said Darrell West, a Brown University political scientist. “There are going to be stark political consequences. As we lose political representation in the House, it affects which laws get passed and how the federal budget gets divided up.”

With each House seat lost, a state also loses representation in the electoral college, which diminishes its weight in presidential elections. Congress also uses census data to determine how much money each state gets for government programs, including Medicaid.

New Hampshire is projected to see 33 percent growth by 2030, the region’s fastest growing state, followed by Vermont with 17 percent and Maine at 11 percent. Massachusetts and Rhode Island are expected to see 10 percent growth and Connecticut would see 8 percent growth – one of the lowest rates in the country.

Political scientists predict the population shift will change everything from zoning regulations to control senior housing to which committee appointments senators and representatives seek in Washington.

“The key is for senators and representatives from the Northeast to work for positions of influence on regional issues,” said L. Sandy Maisel, director of the Goldfarb Center for Public Affairs at Colby College in Maine. “As a region, you lose some of your ability to become really influential on, say, foreign affairs.”

But not everyone is ready to write off New England as political dead weight.

“It’s not our electoral college base that’s been the source of political clout in New England,” said Garrison Nelson, a University of Vermont professor who also has taught classes on New England politics at Boston College. “Massachusetts has been losing seats for a while, since 1930, yet three presidential nominees have come out of Massachusetts in the last 50 years.”

Nelson and others argue that the New Hampshire primary and the power of New England universities, particularly Yale and Harvard, will keep the region influential.

“We’re going to train the future presidents,” West said. “They’re going to be attending college in this area. We have to hope that affects their outlook and makes them sympathetic to the region.”