BANGOR – U.S. Sen. Susan Collins held on to a sizable lead over her Democratic challenger Chellie Pingree, according to a poll commissioned by a media consortium including the Bangor Daily News.

Collins won the support of 60 percent of likely voters compared to 28 percent for Pingree, the former state senator and majority leader, according to the September telephone survey of 523 likely voters.

The 32-point spread had Pingree aides doubting the validity of the RKM Research and Communications survey, citing their own internal polls that placed the well-financed North Haven Democrat within 9 percentage points of the one-term Republican incumbent.

“We have a lot of confidence in our polling numbers and we feel good to be where we are at this point,” said Pingree press secretary Deborah Barron. “Nobody votes on polls and voters know Chellie is on their side on the issues that matter.”

The RKM poll was conducted Sept. 7-10 for WLBZ 2 Bangor, WCSH 6 Portland, the Bangor Daily News and Maine Public Broadcasting.

In the poll, 8 percent of the likely voters surveyed were undecided.

One of the poll’s more dramatic numbers was the near quadrupling of likely voters who say they had an unfavorable opinion of Pingree since a May poll conducted by the same firm.

In the new poll, Pingree’s negatives ran at 24 percent – nearly equal to her favorable ratings – compared to her 6.5 percent unfavorable rating in May.

While the Pingree campaign downplayed the numbers, Collins aides jumped on the statistic, saying that Pingree’s negative television ads would be her downfall.

“Chellie Pingree’s allies have run seven negative ads against Senator Collins thousands of times across the state over the past year, to no avail,” said Felicia Knight, the Collins campaign’s communications director. “Mainers have looked beyond this unprecedented barrage to Senator Collins’ record of significant accomplishment.”

Political analysts said the Pingree campaign, despite the brave face, has to be disappointed in the poll results, particularly the high negative numbers.

“They have to be at least a little nervous, but there’s still a lot of people who haven’t formed an opinion of [Pingree,]” said University of Maine at Farmington political science professor Jim Melcher. “I would think the concern would be more that more people haven’t formed a positive opinion of her.”

Pingree, who campaigned with U.S. Sen. Hillary Clinton, D-N.Y., Friday evening, has expressed her own objections about personal attacks in GOP ads.

Barron said Friday that she was confident that Pingree’s involvement with health care reform and prescription drug legislation would resonate with voters, who cited both issues among their top concerns in the RKM poll.

“The issues that matter are at the top of Chellie’s agenda, and the poll suggests Chellie’s message is getting through,” said Barron, who reiterated the challenge to Collins to debate six times before the Nov. 5 election.

Knight said Collins would fit as many debates as possible into her busy schedule but has not yet committed to any.

In the poll, 61 percent of likely independent voters said they would vote for Collins, compared to 22 percent for Pingree.

Among likely Democratic voters, Pingree polled at 49 percent to Collins’ 40 percent. Among Republicans, the numbers were 81 percent for Collins and 9 percent for Pingree.