Results of an independent public opinion poll show Rep. Stephanie Herseth (search), D-S.D., continues to lead Republican challenger Larry Diedrich (search), but by the narrowest margin since the campaign began in February.

Herseth leads Diedrich 48 percent to 44 percent in the poll conducted for the Argus Leader newspaper and KELO Television, both of Sioux Falls. Terry Begay (search), a Libertarian candidate, garnered 1 percent of the responses.

Mason-Dixon Polling and Research of Washington, D.C., conducted the poll last Tuesday through Thursday. The telephone survey of 800 likely voters has a margin of error of 3.5 percent.

Seven percent of those questioned were undecided.

Herseth defeated Diedrich by 3,005 votes in a June 1 special House election to fill out the remainder of Bill Janklow's term after he resigned. She received 50.5 percent of the vote in the election.

"Now that margin is larger, according to these results, and I believe that is a direct response to the work I'm doing in Congress," Herseth said of the latest poll results. "I have worked hard to be South Dakota's independent and effective voice in Congress, and I believe that South Dakotans recognize my commitment to doing what's right for our state - not what's right for one party or another."

Diedrich says the results show the fruits of his second campaign to win the seat.

"I think it shows what we are feeling that is extremely tight," he said. "We felt we would have a shot at the 85,000 voters that didn't vote in June. We think they are coming our direction and maybe some the other way."

By region, Herseth had a 54-41 advantage in the Sioux Falls metro area, a 48-43 percent advantage in East River/south and a 52-41 percent lead in East River/north. Diedrich led by a 51-40 percent margin in West River.

Women backed Herseth 51-41 percent, while men supported Diedrich 48-44 percent. Begay consistently garnered 1 percent in most of those categories.

A Sept. 20-22 telephone poll by Mason-Dixon Polling and Research showed Herseth with 49 percent support and Diedrich with 42 percent. Begay had 1 percent. Eight percent were undecided.