Winter came early to Minnesota this weekend, and with it was an icy blast for the Republican Party. A three-year experiment in supply-side economics here has left the Republicans in a shambles, and the once dispirited Democratic Farmer Labor Party has its confidence back.

On Saturday night, Democrats gathered in the small town of Morris in western Minnesota for a party fund-raiser. They call them bean feeds here, but it was really the Republicans who were on the menu. "A lot of people are feeling discontent about the Republicans--both those in Minnesota and in Washington," said Laura Carrington, the DFL county chairman. "I think people who shifted their votes from the DFL are coming back."

If Minnesota, where Republicans capitalized on Democratic disarray and a national swing to the right to score stunning upsets in the 1978 elections, is an indicator, the Republican Party shouldn't get overconfident about the 1982 elections.

What is bringing hope to the DFL in Minnesota are the economic policies of Republican Gov. Al Quie, and Democrats suspect Reaganomics might do the same for them next year. In addition, the DFL has healed many of the wounds that were opened in 1978, and under a new party chairman is diving headlong into the technological world of computers and direct mail, even sending its staff members to a school conducted by New Right direct-mail expert Richard A. Viguerie.

The Republicans' problems worsened last week when word leaked out that the state faced a new and unexpected deficit of at least $500 million to $600 million for the biennium that began in July. That came after Quie was forced to raise taxes and cut spending last spring to bring the budget into balance when revenues fell far short of his earlier projections.

Quie had planned a press conference for Tuesday to outline the state's newest fiscal crisis, but canceled it when he learned that a new pessimistic national economic projection was on the way from his outside consultants. That makes it likely the projected shortfall will swell even more, requiring a new round of budget cuts and tax increases.

As a result, Quie is in political trouble. A poll released today by the Minneapolis Tribune shows two Democrats, Attorney General Warren Spannaus and former governor Rudy Perpich running 2 to 1 ahead of Quie in trial heats. Spannaus has announced his candidacy.

"It's not just the Democrats picking at him now," said Joan Growe, Democratic secretary of state, "it's people in his own party." Quie already faces a challenge within his party, and there is speculation that the former congressman might not run for reelection.

What has put Quie in this position is the tax revolution that he instituted. As governor, he indexed the state's income taxes, promising that the tax cuts would bring economic expansion. Since then, state revenues have not kept pace with expenditures. In addition, Quie's own finance division has issued a series of faulty forecasts that has forced the governor to revise his budget with embarrassing regularity.

"I think anybody would forgive him the first time, but the third or fourth?" said Don Fraser, the Democratic mayor of Minneapolis who served with Quie in the U.S. House of Representatives.

So far, Quie's problems have not spilled over onto Republican Sen. David Durenberger, who is also up for reelection in 1982. Durenberger was the surprise beneficiary of a bitter DFL fight in 1978 between Fraser and millionaire Bob Short. Fraser won the party endorsement, but Short, capitalizing on the issues of abortion, gun control and creation of the Boundary Waters Canoe Area in northern Minnesota, defeated Fraser in the primary. Many Democrats then helped elect Durenberger.

Today, Durenberger remains popular, if not overly well known, but the Democrats believe he could be beaten in 1982 if the national economy has not rebounded. Mark Dayton, a 34-year-old member of the well known department store family here and former aide to Walter F. Mondale when the former vice president was in the Senate, has been crisscrossing the state since last November. He is little known, but is running a well staffed and well financed campaign. Earlier this year, he bought ads in most of the state's newspapers to criticize Durenburger and Republicans for proposed Social Security cuts.

The Democrats also have their eyes on regaining two congressional seats. One is in the 6th District, which went Republican last November. The other is the 7th District. It was held by Bob Bergland until he quit the House to be President Carter's agriculture secretary in 1977. Since then it has been held by Republican Arlan Stangeland. He has twice beaten a young farmer named Gene Wenstrom, but his margin in 1980 was less than in 1978, and Wenstrom is back again for a third try, more confident than ever.

"Unless things are absolutely right for Ronald Reagan, I'll win," Wenstrom said Saturday as he drank coffee in a restaurant on the main street in Morris.

But the DFL has more than eager candidates. The changes at the party's dilapidated headquarters in Minneapolis are also significant. "Frankly, we got fat and arrogant," said Mike Hatch, the 32-year-old DFL chairman. "There was no work being done within this party for five, six, seven years in terms of developing new blood."

Since his election in 1980, Hatch has paid off the party's debts, launched a new direct mail program, ordered a computer and doubled the budget to $850,000. When Viguerie was in Minneapolis conducting a direct mail school, Hatch sent two staffers to learn. "He's the best around," Hatch said.

Intraparty fights, which wrecked the DFL in 1978, are not completely gone. Abortion remains a divisive issue, and party procedures that encourage factionalism have not been eliminated. An attempt to change the rules caused an angry showdown in August, in which Hatch was defeated by a coalition of pro-choice and anti-abortion forces. "The most important thing it did," Hatch said of his losing effort, "was to solidify a moderate base in the party."

The DFL faces the unusual prospect of uncontested primaries for governor and senator and could enter the 1982 elections more united than at any time in recent years. Defeat and exile have made them hungry, and the Republicans are making them confident. Said former Democratic national committeeman Ray Anderson at a bean feed in Audubon, Minn., Saturday night, "I think Reagan and Quie are making the party healthier every day."