Susan Collins pledged to serve just two terms in the Senate, and a state Democratic Party official wants to hold her to that promise.

Collins, a Republican, was elected in 1996 to a six-year term, re-elected in 2002, and is seeking a third term on next year’s ballot. Tom Allen, the six-term Democrat representing Maine’s 1st Congressional District, is challenging Collins for the Senate seat.

Sen. Collins, according to Democratic Party spokeswoman Carol Andrews, made the pledge to serve just two terms while running for the seat in 1996. Collins announced the two-term pledge on April 1, 1996, while signing a document supporting a constitutional amendment limiting terms for members of Congress.

While seeking re-election in 2002, Collins reaffirmed her pledge to serve two terms in a letter to a constituent, according to Andrews.

The Collins campaign does not deny she made the pledges, but has said she underestimated the importance of seniority in the Senate. The Collins campaign also has said her stature in the Senate, as a moderate whose support is sought by members of both parties on key votes, benefits her Maine constituents.

The state Democrats distributed a statement about the term limits pledge, Andrews indicated, after Sen. Chuck Hagel, R-Neb., announced last week that he would not seek re-election, citing a pledge he had made in 1996 to serve just two terms.

Sen. Wayne Allard, R-Colo., also announced this year he would not seek a third term in 2008 in deference to a pledge to serve just two terms. Andrews also noted that Sen. Bill Frist, R-Tenn., honored his two-term pledge last year, even while serving as Senate majority leader.

Collins should follow in these traditions, Andrews said.

“These senators all kept their promises to the people of their states,” she said in the press statement and quoted Allard, who said: “It is a matter of integrity.”

The Collins camp responded that Democrats are raising the pledge issue as a way to smear the incumbent rather than tout Allen.

“This attack is a sign that despite all the money raised and spent more than a year before the election, the Allen campaign is floundering,” Collins spokeswoman Jen Burita said.

Allen’s campaign staff, she continued, “is starting to worry that the only chance he has of getting elected to the Senate is if Susan Collins doesn’t run. When you look at [Allen’s] complete lack of legislative success and his extreme partisanship next to her incredible record of accomplishment, her never having missed a vote, and her independent approach to governing, they know that this race is going to be an uphill struggle.”

Burita said she expected to see more such campaign tactics in the coming months.

The Democratic Party’s statement cites several sources and instances in which Collins made the pledge, including in interviews with newspapers and in her campaign literature.