A new scientific poll on South Dakota's U.S. House race suggests Stephanie Herseth (search) could keep her job come November.

Herseth, the Democratic incumbent, had 49 percent support to Republican challenger Larry Diedrich's (search) 42 percent, according to the poll sponsored by The Argus Leader and KELO-TV, both of Sioux Falls. Libertarian Terry Begay (search) got 1 percent support.

Amy Walter, who monitors U.S. House races for the Cook Political Report (search), said Herseth's role as an incumbent may explain her strong showing.

"It's very helpful for her," Walter said, "plus the fact that she didn't acquire any scars or baggage from the special election."

The statewide poll had a margin of sampling error of plus or minus 3.5 percentage points. It surveyed 800 likely voters by telephone Monday through Wednesday last week.

Eight percent of voters remained undecided.

Herseth defeated Diedrich by 3,005 votes in a June special election to fill the remaining seven months of former Rep. Bill Janklow's House term. A rematch for a full two-year term is set for Nov. 2.

Diedrich said the poll suggests another close fight.

"It's going to be a very tight race again like it was in June," he said. "It tells us it's going to be extremely important to get the vote out. It also tells us we need to continue to do what I've been doing the last several weeks which is talk to people basically from all walks of life."

Herseth said she has been focusing on her new job since the election. "Campaign concerns have been secondary to my work in Congress. I'm glad that voters are viewing my work in Congress favorably," she said.

"The fact that we've gone from a very close Election Day result to a 7-point margin since I've been in Congress indicates that people are pleased with the job I'm doing."

University of South Dakota political science professor Bill Richardson said Herseth probably is ahead but that changing demographics might make polls less reliable than in the past. For example, people who use only cell phones might not be accessible to pollsters because their names often are not in databases, he said.

Eighty-five percent of the Democrats and 19 percent of Republicans supported Herseth. She had a 53-38 edge among women, although men favored Diedrich 46 percent to 45 percent.

Herseth's favorable rating was 51 percent to 45 percent for Diedrich. Herseth's unfavorable rating was 26 percent; Diedrich's was 28 percent.