(Adds quotes from Brown, voters, new poll, changes dateline from BOSTON)
By Scott Malone
PORTSMOUTH, N.H., April 10 (Reuters) - Former U.S. Senator Scott Brown of Massachusetts launched 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.
"So many problems with our economy happened because of Obamacare. And Obamacare could not have happened without a rubber-stamp 'yes' vote from Senator Shaheen," Brown told a crowd of a couple hundred supporters in a hotel ballroom in Portsmouth, New Hampshire, near the state's southern coast.
"Obamacare forces us to make a choice, live free or log on - and here in New Hampshire, we choose freedom," Brown said.
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 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 February poll, which found 53 percent of adults in the state opposing the law and 34 percent favoring it.
Despite the early problems, the White House released figures last week showing that 7.1 million people had enrolled through the new exchanges, 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," said New Hampshire statehouse Speaker Terie Norelli, a Democrat.
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.
Two polls of New Hampshire voters released on Thursday showed him 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.
A WMUR television poll, with a sample size of 387 likely voters found Shaheen with a narrower 45-39 lead.
Brown's strong anti-Obamacare stance drew divided reaction from New Hampshire voters.
Bill Gannon, a 51-year-old theater-curtain business owner from Sundown, said he'd become interested in Brown in part because of his anti-Obamacare message.
"I don't like the new healthcare law," said Gannon, who had joined the crowd in the hotel ballroom to hear Brown speak. "We need the Senate back and this is a guy who's electable."
Outside, 80-year-old Joan Webber of Kensington, New Hampshire, who was holding a sign reading "Scott Brown is a twerp" said he supported Shaheen and the Affordable Care Act.
"He probably has his insurance already," Webber said of Brown. "He just doesn't want the poor to get it." (Reporting by Scott Malone; Editing by Dan Grebler, Ellen Wulfhorst, David Gregorio and Cynthia Osterman)