Dissension about oversight of the $1 billion Minnesota Vikings stadium erupted again Friday with one commissioner's surprise resignation and another questioning whether the chair could successfully direct the state's biggest private-public project to completion in 13 months.

At the end of an hourlong Minnesota Sports Facilities Authority (MSFA) meeting, former state Sen. Duane Benson announced his resignation, saying that in 40 years of public life he had never been treated as badly as he has been by Chair Michele Kelm-Helgen. Benson said that in a phone conversation this year, she called him "untrustworthy" and a "liar." Benson said it would be "untenable" for him and Kelm-Helgen to work together.

Commissioner John Griffith said in a later interview that Kelm-Helgen also called him "untrustworthy" and a "liar" as well.

After the meeting, Kelm-Helgen said she did not call any commissioner a liar.

The two men have publicly pressed Kelm-Helgen on her role in the construction of the stadium, specifically asking why she and MSFA executive director Ted Mondale appear to be doing the same full-time jobs. A similar committee that oversaw the now-departed Metrodome had a full-time executive director and a part-time chair. Mondale makes $162,245 a year. Kelm-Helgen makes $127,000 and has questioned why she makes less.

Kelm-Helgen said she was "disappointed" that Benson "chose to leave at this time and this way" because of a "difference of opinion about my role and pay."

Now Griffith, a former Target executive with a deep resume in construction, is questioning whether Kelm-Helgen has the management skills or experience to stay on as chair for the next year. Even though the project is 60 percent complete, the hard part lies ahead, with an accelerated rate of decisionmaking.

Asked whether he might resign, Griffith paused and said, "Not at this point."

He lamented Benson's departure, saying the two of them believe "friendly friction" is important to good management and policy.

Benson said he told Gov. Mark Dayton that he will step aside as of Aug. 1. Through a spokeswoman, the governor declined to comment on the tension at the MSFA, nor would he say when he plans to replace Benson.

The MSFA provides public oversight of the construction of the stadium, nearly half of which is paid for by taxpayers in Minnesota.

MSFA meetings are among the few public opportunities to get updates on the project costs and adjustments. Usually, Kelm-Helgen leads the sessions with updates on the progress on the project, the status of equity hiring, design changes and the approval of more money from the Vikings. Citizens often use the public forum time to urge the use of bird-friendly glass on the building.

Before Friday's tense final minutes, the MSFA approved an additional $5 million from the team, most of which is going toward the wireless Internet system.

Benson said he had notified the governor months ago that he would be leaving, but he postponed the announcement until after the Legislature adjourned to avoid being a distraction. In April, a budget committee in the Republican-controlled House proposed eliminating Kelm-Helgen's salary because of concern for an overlapping role with Mondale.

Upon hearing Benson's news, Griffith said it was "pretty disappointing." Fellow board members Bill McCarthy and Barbara Butts Williams said nothing.

Kelm-Helgen then started to speak, saying Benson had changed his position the day after their phone conversation.

Benson stopped her short, saying, "I would just as soon not try the case."

Resignation isn't resolution

Kelm-Helgen and Benson both have deep roots in Minnesota politics. She grew up in a well-known DFL family and worked mostly behind the scenes in Dayton's office before he appointed her chair.

Benson, a Republican who lives in Lanesboro, has a career that includes 14 years in the Minnesota Senate and nine years at the helm of the Minnesota Business Partnership, working with CEOs from the state's largest corporations. He's been a trustee on the board of the Minnesota State Colleges and Universities since 2004.

What makes his action particularly notable is that despite a long career in the political ring, Benson is known for his pragmatic politics and equanimity.

Minnesota Vikings Vice President Lester Bagley, who worked as Benson's deputy for five years at the partnership, was the first to pull Benson aside after the meeting. "He's a man of integrity, and he's a great guy," Bagley said. "It's disappointing he won't be here."

In a conversation later, Benson said he still doesn't have answers to his main questions. "I've always asked this question over and over: How can we have two people doing the same job?"

Kelm-Helgen later responded that Benson has the answer and just doesn't agree with it.

But Griffith still wants answers, and he suggested the board might be better served by rotating chairs because of what he called Kelm-Helgen's lack of experience in construction and the difficulty of managing an organization when two people are trying to make decisions. "You want to have one person in line to do the job and have all the authority and responsibility," he said.

In response, Kelm-Helgen said she wants to focus on the job, not prolong the debate. "However, I must say, in my career and in this job, I treat people with respect," she said in a statement.

Star Tribune staff writer Mike Kaszuba contributed to this report. Rochelle Olson • 612-673-1747 Twitter: @rochelleolson