The reason for the Carter campaign's panicky late attention to the Wisconsin primary can be seen in the reaction of La Crosse Central High School students when Vice President Walter Mondale opened his speech with an anecdote about Jimmy Carter.

"Just before I left Washington, I had lunch with the president," said Mondale. Before he could continue, the well-mannered, well-scrubbed Midwestern boys and girls interrupted him with apparently involuntary laughter that sounded a little like jeering.

That typified the reaction toward Carter in a state where he led all Democratic opponents by 50 percentage points in polls a week ago. Although high school students usually applaud at any excuse, Mondale's praise of Carter administration exploits was greeted by stony silence at Central High. Earlier in Racine, a United Auto Workers political action group was not much more enthusiastic. The night before in Green Bay, Rosalynn Carter was heckled by unemployed construction workers.

The consolation for the Carter campaign is obvious lack of support for Sen. Edward Kennedy. Unhappy though Wisconsin is with Carter, it seems even cooler toward Kennedy (who a week ago was running third behind Gov. Edmund Brown Jr.). But wasn't this precisely what was said before Kennedy's upsets in New York and Connecticut? Two hard days of Kennedy campaigning here yesterday and today might make it close enough to be uncomfortable for Carter.

Thus, Mondale was gloomly when he arrived in Wisconsin from Texas at 2 a.m. in his unending jorney as stand-in for the Rose Garden-bound president. As part of the new attention on Wisconsin that sent a half-dozen Carter political operatives flying here, Mondale had been assigned another day in the state (spoiling plans for a skiing respite). Apart from personal inconvenience, he saw a war of attrition reaching Madison Square Garden in August.

Mondale's first appearance was before the UAW political activists, supposedly pro-Carter. But while walking around the lobby of the Racine Motor Inn, it was hard to find Carter sentiment. Again, the consolation for the White House was lack of Kennedy backing. "I think you'll find a lot of the guys on the assembly line going Republican this time," one UAW operative confided.

Nor is there an abundance of pro-Carter sentiment at higher levels. Ray Majerus, UAW leader in Wisconsin, was recently chided about his Carter endorsement by Wisconsin's ex-governor, Patrick J. Lucey, who is national vice-chairman of the Kennedy Campaign. Majerus, about to become the UAW's internatinonal secretary-treasurer, replied that he had to back Carter because the union's other top leaders support Kennedy.

Whatever the real motive, the UAW support for Carter here seems passive (lacking even the union's habitual telephone bank). That is one reason Lucey, whose solitary travels here constituted the whole Wisconsin Kennedy campaign, pressed for an 11th-hour effort.

Kennedy campaign manager Steve Smith, arguing with Lucey the morning after the New York-Connecticut wins, pointed out that John F. Kennedy's 1960 primary campaign had operations in every county of Wisconsin. Yes, replied Lucey, but so did his opponent's, Hubert Humphrey; Jimmy Carter has nothing approaching that.

Consequently, it was decided to bring in Kennedy for the two days before the election and devote the trifling sum (perhaps less than $200,000) for television commercials. There is neither the money for paid media nor the time for free media in the volume that turned the tide for Kennedy in the East.

Nevertheless, those Eastern victories were enough to bring out two prestigious closet-Kennedyites who never would have considered an endorsement otherwise: State Attorney General Bronson LaFollette, bearer of Wisconsin's most famous political name, and Rep. Henry Reuss, chairman of the House Banking Committee.

LaFollette accused the absent Carter of conducting "a phantom campaign." Surrogate Mondale responded quickly that "the president is not hiding" and "we need our president working for us and not preoccupied with the campaign."

But Mondale on the stump here usually says little about Carter (and nothing about Kennedy). The vice president's New Dealish speech, extolling the joys of bread-and-butter liberalism, won only perfunctory applause from UAW political activists. Even if he wins Tuesday as expected, Carter is in deep political trouble, which cannot be resolved by his vice president's tireless barnstorming.