MINNEAPOLIS, OCT. 19 -- Envision a roller coaster, the kind that loops upside down and leaves its passengers weightless, disoriented and mildly queasy.

That's what Minnesota politics has been like this week.

Voters, candidates and political activists accustomed to this state's tradition of polite and civilized politics are reeling from the impact of nearly daily revelations about alleged sex habits, investigative diligence and veracity of the two nominees for governor.

Businessman Jon Grunseth, 44, the Republican candidate, had been nipping at the heels of Democratic incumbent Rudy Perpich in statewide polls until this week, when three women accused him of swimming nude with them at a 1981 pool party and serving alcohol to his party guests, ages 13 to 16 at the time. One of the women said Grunseth cornered her in the pool and attempted to grab her breast.

The allegations, made in sworn affidavits by childhood friends of Grunseth's daughter, Nina, have been vehemently denied by the GOP candidate. But they have crippled his campaign and overwhelmed everything else in Minnesota politics -- including the spirited underdog challenge to Sen. Rudy Boschwitz (R) by college professor Paul Wellstone (D).

During the last tumultuous week, Grunseth was urged to resign and responded by taking a $300 lie detector test in an attempt to mollify his critics and state GOP officials. By week's end, he gathered his supporters yards from Perpich's office on the steps of the state capitol to declare that he is in the race to stay.

At least one of the GOP primary challengers he defeated, State Auditor Arne Carlson, had indicated he would not mind stepping into the breach with a scant three weeks left in the campaign.

Minnesotans, who relish their state's reputation for progressive, clean politics, are rocked.

"I've never seen anything like this in politics," said Boschwitz in remarks to local Republican business leaders via speaker phone from his Capitol Hill office Thursday. "This is more appropriate for Texas and Louisiana than it is for Minnesota."

The pool party incident -- which has spawned a cottage industry of tacky jokes and caused one local columnist to muse whether anyone could ever cast a ballot for a candidate they had imagined unclothed -- is only the latest episode in Minnesota's 1990 catalogue of political embarrassment.

"This has evolved into a family feud, and then into sex, lies and videotape," said Mike Dunstan, a Republican who is organizing a write-in campaign for Carlson.

Secretary of State Joan Grow (D), who was drawn into the controversy when she announced it would be constitutional to place a new Republican name on the ballot, noted that this is just the latest twist in a very odd year for Minnesota politics.

"This has not been a good year for us, with Durenberger and everything else," she said. "My God."

Earlier this year, Sen. Dave Durenberger (R) was publicly censured by the Senate for ethics violations. And in the 7th Congressional District, Rep. Arlan Stangeland (R) has been accused of making hundreds of phone calls at taxpayer expense to the home of a female lobbyist in Virginia. He said the calls were business-related.

But it is the Perpich-Grunseth debacle that has set new records for consecutive front-page headlines here. Both Grunseth and Perpich rack up high negatives in polling. Each has trotted out a wife or daughter to defend him in television ads. The typical voter response appears to be disgust.

"Quick, tell me who the other candidates for governor are," Sandra Troska wrote in a letter to the St. Paul Pioneer Press.

"It's too bad, and I can't wait for this thing to get done," said Democratic Farmer-Labor Party chairman Todd Otis.

Perpich, who is seeking his fourth term in office and has served longer than any other Minnesota governor, has gained a reputation as a thin-skinned politician who does not hesitate to strike out at his enemies.

Responding to criticism of what one newspaper article described as his "lavish" lifestyle earlier this year, Perpich turned in his leased Lincoln Town Car and canceled his driver. His wife, Lola, offered to sell the governor's mansion.

A week ago, Perpich toured the state handing out copies of Grunseth's divorce papers that outlined the bitter disputes fought in court between the Republican nominee and his ex-wife.

"It's not good for the state, obviously," Perpich said of the latest brouhaha that he insists he did not engineer. "But the fact is that character is a very important part of the process . . . "

He said Minnesota politics will be irrevocably changed by the campaign, but for the better.

It is difficult to find anyone who agrees with that optimistic assessment.

Wellstone, a diminutive and energetic campaigner who has gained attention through his offbeat advertising and populist stump speeches, sees the crucial last weeks of the campaign slipping through his fingers as the voters' focus remains on the governor's race.

Boschwitz, one of the Senate's most prolific fund-raisers, plans to spend $1 million on television advertising in the campaign's closing weeks. Wellstone, who travels the state in a refurbished green-and white school bus, has $82,000 in the bank.

A long-awaited debate between the two occurred last Sunday. But the Grunseth pool party stories hit the next day. "We had that debate Sunday night and we had great press," said Mark Anderson, a Wellstone aide. "Then Monday, the bomb dropped."

The Wellstone camp, hoping perhaps for a little of the notoriety that negative campaigning can bring, has prepared a response ad should Boschwitz go on the attack. It features Wellstone's handsome portrait being splattered with mud.

But Boschwitz aide Jay Novak, noting the "disappointment" and "disgust" already evident among voters this fall, said the senator does not plan to go negative.

While Boschwitz may benefit from the fallout from the governor's race by remaining above the fray in Washington, Grunseth and Perpich have hunkered down for a nasty fight to the finish.

Grunseth has demanded that Perpich and his aides also take a lie detector test. Perpich said he won't.

On the edges of the Minesota fray are a forlorn group of activists who had hoped to inject a discussion of the issues into this year's campaign by creating "citizen juries" to evaluate each candidate on education, the environment and taxes.

The 18-member jury meets next week to review each candidate's record and interview them. Perpich, who did not rate well in the jury process during the primaries, has declined to participate this time around.

Said Ned Crosby, who runs the jury project: "We think we provide a service even though in the current environment, maybe only 5 percent {of the voters} will be paying attention."