Washington ? Democrats celebrated Stephanie Herseth’s capture of a Republican-held seat in South Dakota on Wednesday, their second takeaway of the year, and claimed it portends greater gains in the battle for control of Congress.

Republicans argued that local factors settled the race, but some conceded privately that a sour national mood and President Bush’s slumping support contributed to the defeat of GOP contender Larry Diedrich.

“It’s time to put partisan politics aside,” said Herseth, who squeaked to a 2,981-vote triumph in an election that drew heavy investment from the two parties seeking momentum for the fall. Turnout was large, with more than 261,000 ballots cast.

Herseth, the 33-year-old daughter and granddaughter of prominent politicians, is expected to take her seat today to fill out the unexpired term of former GOP Rep. Bill Janklow. That would shave the Republican advantage in the House, and mean Democrats must win 11 more seats this fall if they are to gain control.

Democratic lawmakers were quick to trumpet Herseth’s victory, three months after Rep. Ben Chandler was elected in Kentucky to a seat that had been in Republican hands.

“I don’t think there’s any question what the American public seeks, which is the wind of change. People are unhappy with the status quo,” said Rep. Bob Matsui, D-Calif., chairman of the Democratic Congressional Campaign Committee.

Rep. Steny Hoyer, the House Democratic whip, said that “because of the energy for change, we are going to be able to put more seats in play” in November. The Maryland lawmaker argued that 35 to 40 seats are competitive at this stage, meaning that Democrats must win two-thirds if they are to mount a serious challenge to continued GOP control of the House.

Once Herseth is sworn in, Republicans will have 228 seats and Democrats 206 with one Democratic-leaning independent.

“For Democrats to have any real gains, they’ve got to double the playing field” of competitive seats, said Rep. Tom Reynolds of New York, who heads the Republican campaign committee.

He pointed out that the Democratic election gains had already been negated when Texas Rep. Ralph Hall switched parties to become a Republican last winter and another Texan, Rep. Jim Turner, announced plans to retire and concede his seat to the GOP.

As for Herseth’s victory, Reynolds said, “There are no national implications in South Dakota. … It’s as much local issues as any race I’ve ever seen.”