One reason why Republicans may win two Senate seats and the governorshop from centrist Democrats in Hubert Humphrey's Democratic-Farmer-Labor (DFL) Party is the insatiable demand of the DFL left wing for ideological purity.

The DFL purity test has been getting harder to pass year by year. Now it threatens to undermine the party at a critical point, challenging DFL control of this state that started in the mid-'40s. The party won every statewide office and the legislature in 1972 for the first time in history, and has given Minnesota widely acclaimed progressive government.

Meeting the test was expensive for Rep. Don Fraser, one of the stars of the DFL left-wing elite. Businessman Robert Short, long connected to the moderate-conservative wing of the party, beat Fraser in the DFL senatorial primary, and Short's emphasis on cuts in taxes, spending and government payrolls was only a partial reason.

"Fraser hung on to his elitist ideology against heavy odds," a moderate DFL leader told us. "He just couldn't carry all that pro-abortion, pro-gun control and pro-environment baggage." The real majority in this state is probably anti-abortion and anti-gun control, and it wants outboard motors and snow-mobiles in the Boundary Waters area.

With the primary election two weeks past, Fraser is still sulking and the DFL left is threatening revenge against Short. This matches shabby treatment in the past for Humphrey himself, the founder of the DFL.

For his sins as Vietnam War supporter while vice president, Humphrey was challenged in his 1970 Senate comeback by a DFL liberal backed by purists of the left. Humphrey beat him, but the left wing then rewarded him with the post of national committeeman.

Short's running partner in the second Senate race this fall is incumbent Sen. Wendell Anderson, a DFL moderate whose refusal to kowtow to the elitist left wing also brought a liberal challenge in the Sept. 12 primary. The challenger rolled up 38 percent of the vote, but Anderson refused to bargain away his more moderate position on abortion and the hot issue of banning motors in the Boundary Waters area.

The power of liberal activists was dramatically exposed at the 1976 DFL convention. Steamrollering the party's center, clearly a majority, the pro-abortion feminist bloc made a devil's pact with its greatest enemy, the pro-lifers (who oppose abortion) and elected two national committeewomen: an all-out anti-abortionist and an all-out pro-abortionist. The middle-ground majority was ignored.

Under successive waves of party "reform" the past decade, party rules now do more to advance the "rights" of minorities (including, for example, gay rights) than accommodating the non-activist majority. State party chairman Rick Scott, a liberal, acknowledges the problem. "Something is happening in this state," he told us, "but we don't quite know what it is."

In the hamlet of Montevideo one evening last week, a Chippewa County Dfl official listengin to Short make his appeal for party support was impressed. "There won't be an anti-Short campaign here," he told us. Likewise, Lt. Gov. Alec Olson warned that same evening that "the DFL may not last long" if it doesn't shed its suicidal tendencies to please single-issue minorities. He pleaded for support for Short, Anderson and Gov. Rudy Perpich, who is running against highly respected Rep. Al Quie for governor.

But Chippewa County DFL-ers have little in common with the activist left in the twin cities, where resentment of Short for defying its diktat - and of Anderson for being "moderate" - runs highest. Party chairman Scott has received an outpouring of mail and phone calls from angry liberals demanding short's defeat in November.

The Republicans are in especially good position to exploit this disarray. Short faces attorney David Durenberger, a moderate who may pick up many DFL defectors who have it in for Short; ANderson's opponent, self-made millionaire Rudy Boschwitz, roared into a sizable summertime lead over Anderson and still holds it.

Whatever November may bring, the DFL is deep in soul-searching, worrying that the price of ideological purity is wrecking the party. That is no phenomenon for Republicans, whose right wing has always made suicidal ideological demands. For the party of Hubert Humphrey, it is a legacy he never intended to leave.