By Gary Robertson
RICHMOND, Virginia (Reuters) - U.S. Senator Mark Warner holds a 15-point lead among Virginia voters over Republican challenger Ed Gillespie, but the Democrat's support for Obamacare could cost him votes in the November election, according to a poll released on Thursday.
Warner is favored by 46 percent of voters as he seeks a second term, compared with 31 percent for Gillespie, a former chairman of the Republican National Committee, according to the Quinnipiac University survey. Libertarian Robert Sarvis has 6 percent backing.
Warner voted in 2010 for the Affordable Care Act, or President Barack Obama's signature healthcare reform, which has had a troubled launch. Virginia voters oppose the healthcare law 52 percent to 44 percent, the poll showed.
Voters in Virginia, a swing state in presidential elections, said 45 percent to 31 percent that they were less likely to vote for a Senate candidate who supported the health care law.
Warner has said that he was upset by the difficult roll-out of the Affordable Care Act. He has urged supporters and opponents of the legislation to work together to solve its problems.
Gillespie, a former Washington lobbyist and counselor to Republican President George W. Bush, opposes the Affordable Care Act.
Warner is among the third of the 100-member Senate up for election in November. Republicans believe they have a good chance to pick up the six seats they need to take control of the Senate based on public dissatisfaction with Obama and concerns about Obamacare.
Democrats are defending 21 seats, including Warner's, to 14 for Republicans.
Voters say 33 percent to 15 percent they would be less likely to vote for Warner if Obama campaigned for him, the poll showed.
Peter Brown, assistant director of the Quinnipiac University Poll, said Warner enjoyed high name recognition and a strong job approval rating, at 55 percent.
He is in the range that suggests that an incumbent is a heavy favorite for re-election, Brown said in a statement accompanying the poll.
Gillespie, who has never held elective office, still has to introduce himself to Virginia voters, though his background in national politics will help him raise money, Brown said.
The poll of 1,288 voters was conducted March 19 to 24 and has a margin of error of 2.7 percentage points.
(Editing by Ian Simpson and Stephen Powell)