Sept. 14 (Bloomberg) -- Former Governor Jeanne Shaheen of New Hampshire, a Democrat, said today that she will challenge incumbent Republican John Sununu for the U.S. Senate next year in a rematch of their 2002 race.

Sununu won by about 20,000 votes in their earlier matchup, and polls conducted this year showed Shaheen with a 20 percentage-point lead over Sununu.

Shaheen's decision, along with the announcement yesterday by former Governor Mark Warner that he's running for the Senate from Virginia, boosts the Democratic Party's bid to widen its 51-49 majority in the chamber. There are 22 Republican-held Senate seats up for election next year, compared with 12 seats held by Democrats.

Shaheen is resigning today from her position as director of Harvard's Institute of Politics in Cambridge, Massachusetts, to focus on her campaign, she said in a statement.

``We've proven in New Hampshire that we can work together to get things done,'' Shaheen said in the statement. ``I want to take that common-sense approach to Washington and help get this country moving in the right direction.''

Sununu won his first term in 2002 over Shaheen with 51 percent of the vote. Last year, two incumbent House Republicans in the state -- Charles Bass and Jeb Bradley -- lost their seats. Sununu's race is rated competitive by the nonpartisan Cook Political Report.

Shaheen led Sununu 56 percent to 34 percent in a Concord Monitor poll of likely voters conducted in July. A spokesman for Sununu didn't immediately respond to a request for comment.

To contact the reporter on this story: Laura Litvan in Washington at llitvan@bloomberg.net

Last Updated: September 14, 2007 13:05 EDT