SALT LAKE CITY — GOP Gov. Gary Herbert said Tuesday he "would stand up against" negative ads about his Democratic challenger, Salt Lake County Mayor Peter Corroon.

A series of TV commercials critical of Corroon were reportedly shown by R&R Partners, the same advertising agency handling the governor's campaign, to a focus group last week to gauge how the spots would be viewed by voters.

Herbert told the Deseret News he had no knowledge of the ads and did not want to see them aired.

"I would not want that to happen," he said. "I would stand up against it from happening."

Asked if he was comfortable with the commercials being shown to the focus group, the governor said, "There are probably a lot of things that go on in a political strategy."

Bob Henrie, the head of R&R Partners, said the agency conducted and paid for the focus group. He said such groups are routinely used "to test concepts and possible future messages."

Henrie said "while a responsible ad firm will give its clients a range of options from which to chose … the only direction R&R has been given by the Herbert campaign is 'to maintain a dignified, positive and issues-focused campaign.' " He did not provide details about the ads.

However, mortgage analyst Milton Monson said he was one of about a dozen participants in a focus group that saw a number of ads criticizing Corroon.

Monson, who described himself as "leaning towards Corroon" in the upcoming special gubernatorial election, said the most effective ad pointed out large campaign contributions accepted by the mayor.

Among the other ad subjects, Monson said, were Corroon sending his children to private school, raising county taxes and fees, associating with liberal Democrats and supporting tax credits for renewable energy.

"My feeling was that was the point of the focus group, to see how people would react to these commercials, and how they would feel about Herbert if he were to go down this route," Monson said.

The focus group, he said, thought the governor should fight back against Corroon's negative ads. "They thought it would seem weak or something if he didn't respond," Monson said.

He said he felt "uneasy" about the ads and described them to a friend. That friend passed along the information to the Corroon campaign.

"I just don't think some of the negative things they're saying are probably the most important issues they should be discussing," Monson said. "I think there's a better way to do it."

Herbert said he won't let his campaign go negative.

"I plan to run a positive campaign to the end," he said. "As opposed to my opponent, who is running very negative campaign ads, I'm not going to do it. I'm running a positive ad campaign and you can take that to the bank."

That may be the best strategy at this point, said Kirk Jowers, head of the University of Utah's Hinckley Institute of Politics and an adviser to the governor.

Going negative now "doesn't seem to make sense," Jowers said, although it's typical for campaigns to have negative ads ready just in case. "If you're ahead, you may never pull that out. If it's tight, you want to be ready," he said.

Corroon's negative ads about the influence of Herbert's campaign contributions on the award of state contracts worked for a while, Jowers said, "but he seemed to stay too long with that approach and the public is turning against him."

Jowers said that shift is documented by both campaign polling as well as the Hinckley Institute class rating the civility of campaign ads for Deseret Media Companies, owner of the Deseret News and KSL.

Herbert said "everybody's uncomfortable with the Peter Corroon campaign ads. The only disappointment is that Peter Corroon is not uncomfortable with this and he should be."

Corroon said the governor shouldn't be complaining.

"I think this shows the hypocrisy of the Herbert campaign," the mayor said. "I'm just showing the facts and the truth and now he's got his negative ads ready to go."

He said it doesn't matter whether Herbert asked for the ads.

"That's nonsense," Corroon said. "If they're involving the campaign, Gary Herbert has some say and some control over them."