Heitkamp has 49 percent support to Berg's 48 percent support, with 3 percent undecided.
Berg has gained support since the firm last surveyed the race, in early October. Then, he had 43 percent support to Heitkamp's 48 percent support.
The poll was conducted by Steve Leuchtman, a former Gallup pollster, of Pharos Research Group. He's also polled the Senate races in Ohio, Pennsylvania and Montana, among others. The firm surveyed 807 likely North Dakota voters with live calls via cellphone and landline from Oct. 19-21; it has a margin of error of 3.4 percentage points.
The North Dakota Senate race has seen few polls, but those that have been conducted have shown Berg ahead by as much as 10 points. That poll came under fire from Democrats who said it oversampled Republicans. Another, from conservative pollster Rasmussen, gave Berg a 5-percentage-point lead, but did not reveal its polling breakdown.
This new poll samples Republicans and Democrats at nearly the same party breakdown reported in 2008 exit polling; then, about 28 percent of North Dakotans identified themselves as Democrats and 38 percent identified as Republicans. This poll surveyed 27 percent Democrats and 41 percent Republicans.
--This post was updated at 5:13 p.m. to reflect Rasmussen polling numbers.