Berg leads Heitkamp, the former state attorney general, 51-44 in the poll by Forum Communications Co., which owns multiple newspapers in North Dakota.

Democrats dismissed the poll as laughable, pointing out that the pollster, Essman/Research, polled likely primary voters and not general election voters. Berg has a primary challenge, but is expected to easily win the GOP nomination. Democrats noted that less than half of general election voters have historically cast ballots in primaries in North Dakota.

Independent polling is in short supply in North Dakota, where state law bars firms from using automated telephone surveys, which are less expensive to conduct. Republicans see retiring Sen. Kent Conrad’s (D-N.D.) seat as one of their strongest pickup opportunities for 2012.

The poll of 500 likely primary voters was conducted May 3-8 and had a margin of error of plus or minus 4.3 percentage points.

The Hill rates this race a toss-up.