The Siena Research Institute found 41 percent of voters in the sprawling district along the Canadian border back Hoffman while 36 percent support Owens.
Six percent said they were still for Republican Diedre Scozzafava who dropped out over the weekend and endorsed Owens. But much of Scozzafava's support appears to have moved into the undecided camp.
"Hoffman continues to demonstrate momentum ... It appears, however, that the majority of Scozzafava's supporters have gone to neither Hoffman nor Owens, but rather into the undecided column, which has doubled since Scozzafava ended her candidacy," said pollster Steven Greenberg.
The poll of 606 register voters, conducted Sunday after Scozzafava bowed out, had a margin of error of plus or minus 4 percentage points.
The special congressional election, one of only two in the country, has garnered attention beyond New York as Republicans fight over the future direction of their party. Conservatives successfully forced Scozzafava, a moderate, from the field with TV commercials saying her support of abortion rights, gay marriage and labor unions was too liberal.
Stung by the criticism, Scozzafava threw her support to Owens, a lawyer from Plattsburgh. Hoffman, an accountant who lives just outside the district in Lake Placid, was backed early by Republican conservatives who may run for president in 2012, including former Alaska Gov. Sarah Palin, former U.S. Sen. Fred Thompson of Tennessee and Minnesota Gov. Tim Pawlenty.
VOTERS GUIDE: Click here for our profiles of Long Island candidates on the ballot for election day 2009