(New throughout, adds new poll, quote from Democrat)
By Scott Malone
BOSTON, April 10 (Reuters) - Former U.S. Senator Scott Brown of Massachusetts plans to launch a Republican campaign on Thursday to represent neighboring New Hampshire in the Senate, with an attack on incumbent Democrat Jeanne Shaheen's vote for Obamacare.
Brown, who moved to his native New Hampshire late last year to explore a run for office, has focused much of his energy on attacking the Affordable Care Act, an issue Republicans are making a centerpiece of 2014 campaigns.
"I worked with Senator Shaheen in the U.S. Senate for three years. She is a nice person, but wrong on the issues facing the people of New Hampshire," Brown will tell supporters in Portsmouth, New Hampshire, according to excerpts of his planned remarks provided by his spokeswoman.
"She made that clear when she cast the deciding vote that forced Obamacare on this state and our country," he will say.
The Affordable Care Act passed the U.S. Senate in 2010 by a margin of 60-39, with all Democrats, including Shaheen, voting in favor of the measure, which was President Barack Obama's top domestic priority.
Technical glitches plagued the new system's rollout. Obamacare is less popular in New Hampshire than nationally, according to a poll of voters in the New England state released in February, which found that 53 percent of adults opposed the law, while 34 percent favored it.
Despite the early online registration problems, the White House released figures last week showing that 7.1 million people had enrolled through the exchanges set up by the act, exceeding most expectations.
New Hampshire Democrats note that the state's legislature recently voted to accept federal subsidies expanding the Medicaid health care program for the poor in New Hampshire, a move made possible by the Affordable Care Act.
"Scott Brown may find that what he thinks the public's attitude here in New Hampshire is may not be what he finds when he gets around the state because repealing the Affordable Care Act means repealing health care for 50,000 citizens," New Hampshire statehouse Speaker Terie Norelli, a Democrat, told reporters on a conference call.
Before any matchup with Shaheen, Brown faces a competitive Republican primary in September, with his leading rival Bob Smith, a conservative who is trying to reclaim a seat he held from 1990 to 2003.
Brown has already won support from national Republican groups eager to reclaim a majority in the Senate, which Democrats currently control by 55 seats to the Republican's 43.
A poll of New Hampshire voters released on Thursday showed Brown gaining ground on Shaheen. Public Policy Polling found 49 percent of 1,034 New Hampshire voters would vote for Shaheen and 41 percent for Brown in a head-to-head matchup. Prior polls had given Shaheen, a former governor, a wider lead on Brown.
Brown's candidacy has quickly become a top concern of state Democrats who began raising his specter in fundraising e-mails after his move to the state.
"Both parties are clearly going to be putting money into this because there are about 10 seats that could flip and this is obviously one that Democrats want to hold," said Shep Melnick, a professor of political science at Boston College who has been active in New Hampshire Democratic politics.
"The money thing will probably be a wash because if it looks competitive, both sides will pump money in," he added. (Reporting by Scott Malone; Editing by Dan Grebler, Ellen Wulfhorst and David Gregorio)