WASHINGTON — Maine Sen. Susan Collins, a Republican, ended 2013 with more than $3 million in her re-election campaign fund but was outpaced in fundraising by her Democratic challenger during the final months of the year.

Collins reported raising $314,921 during the last quarter of 2013. After expenses, the Collins campaign had slightly more than $3 million in cash still available as she seeks a fourth six-year term in the U.S. Senate, according to reports filed Friday with the Federal Election Commission.

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Democrat Shenna Bellows reported raising $332,241 between late October when she officially joined the race, and Dec. 31. Bellows ended the year with just over $233,000 remaining in her campaign account, underscoring the steep financial disadvantage she faces in challenging a well-established incumbent.

Collins’ campaign focused in the $3 million “cash on hand” figure in a release.

“I am confident that we will have the resources necessary to wage a vigorous campaign,” Sam Ladd, vice chairman of People’s United Bank in Southern Maine and the Collins campaign’s finance chairman, said in a statement on Friday evening. “Susan continues to enjoy widespread support from all across the state, and she looks forward to being on the campaign trail later this year.”

Bellows’ campaign has suggested that her late-2013 fundraising was a sign of enthusiasm among potential voters.

The former executive director of the American Civil Liberties Union of Maine, Bellows has been active in Maine policy debates for years but is running for political office for the first time.