More than half of U.S. adults used the Internet to participate in the 2008 election -- the first time that threshold has been crossed, according to a study released Wednesday.

Some 55 percent searched for political news online, researched candidate positions, debated issues or otherwise participated in the election over the Internet, the Pew Internet and American Life Project found.

New forms of Internet communication such as blogs, social-networking sites like Facebook and video-sharing sites played a prominent role, the nonprofit group said. Among its findings:

* 45 percent of Internet users watched online videos related to politics or the election;

* 33 percent of Internet users shared political content with others;

* 52 percent of those on a social network used it for political purposes.

The Internet has grown steadily as a source of political news since 2000, when 11 percent of voters went online to keep up with political developments. That figure now stands at 26 percent. Among young voters and those with broadband connections the Internet has eclipsed traditional media like television, radio and newspapers, the survey found.

Democratic presidential candidate Barack Obama used the Internet to mobilize an army of volunteers that helped him defeat Republican John McCain in the November 4 election.

Obama supporters tended to be more engaged online than McCain backers, the study found. While 26 percent of Obama supporters active on the Internet posted their own thoughts or other content in an online forum, only 15 percent of McCain-backing Internet users participated, for example.

The nonprofit group surveyed 2,254 adults between November 20 and December 4, 2008. The survey has a margin of error of 2 percentage points.

(Reporting by Andy Sullivan, editing by Alan Elsner)

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