Hours after the vote, Walter F. Mondale's strategists sat studying the smudged yellow paper that told them what went wrong in Saturday's Wisconsin state convention straw poll and in their national campaign as another presidential front-runner limped back into the pack.

The paper said that more than 200 delegates who had pledged to vote for Mondale had not felt strongly enough about it to show up at the Democratic gathering on a sunny June day. The former vice president drew 35.7 percent of 2,035 votes cast and finished second to Sen. Alan Cranston (Calif.), who had 38.8 percent.

"Our straw-poll prospects lost out to the sunshine," a Mondale strategist said. He said Cranston's camp was simply better organized, but Cranston also bested the field in the politics of passion.

The Wisconsin straw poll showed again that Cranston attracts fervent, passionate supporters to his candidacy while Mondale does not. Cranston is riding a cause, the nuclear freeze, which is carrying him farther in his long-shot bid for the presidency than many experts thought possible.

In a California straw poll months ago, Cranston won where he could not afford to lose. Then in Massachusetts, he won respect as a distant runner-up to Mondale. Saturday, he stunned Minnesotan Mondale by defeating him in a neighboring state.

Cranston's next straw poll will be before a Young Democrats group in Alabama this week, but Mondale and Sen. John Glenn (Ohio), fourth here behind Sen. Gary Hart (Colo.), said they do not intend to enter.

Cranston, helped here because he bused supporters to the convention and rented hotel rooms for them, was most effective in amassing a core of nuclear-freeze backers in this liberal progressive state.

Results here left the Democratic race wide open, as Hart observed in the wake of his third-place finish. Cranston has become a force to be reckoned with, even though he has yet to develop a truly nationwide constituency, and Mondale is forced to fight fiercely for support from liberals he once felt confidently would be his.

In 1976, liberal Democratic candidates divided their votes in the New Hampshire primary, while conservatives divided theirs in Florida two weeks later, enabling Jimmy Carter to waltz down the middle of the road and into the White House.

Glenn hopes to take a similar path. In the last several weeks, he had pulled virtually even with Mondale after gains in nationwide opinion polls, and Mondale's loss here has renewed interest in Glenn.

Mondale could benefit from a strong showing to restore the faith of supporters and potential contributors, but no showplace is available soon. The next scheduled state straw poll is in New Jersey in September.

So his aides tell reporters that a major test will be which candidate amasses the most funding by the Federal Election Commission filing deadline June 30, who makes a strong showing among party regulars at their meeting in Detroit this summer and who collects the most endorsements.

Endorsements by most prominent Wisconsin Democrats did not win for Mondale here, and endorsements are not likely now to be taken as a fitting measure of his strength.

Mondale's straw-poll tallies showed that supporters from Eau Claire just across the border from Minnesota did not turn up and that he was hurt by no-shows from an inner-city Milwaukee district that includes blacks and Hispanics he counted as his.

Mondale and his top advisers were stunned. An hour before the vote, his campaign manager, Robert Beckel, was asked if there were any way Mondale could lose to Cranston. "No way," he replied.

After the result, Mondale seemed edgy. But by the time speeches began at a party dinner after the vote, he was back in strong form, wowing the $100-a-plate crowd with lines that included his observations about President Reagan's policies on education.

Reagan suggests only two things, "more homework for students and merit pay for teachers," Mondale said. "I have a suggestion. I think we ought to try them both in the White House."

Hart told the audience he had learned a lesson. "I'm going out tomorrow to get a very short haircut," he said, glancing at Cranston's shining pate. The victor merely smiled and chirped: "When Ronald Reagan became president, I had a full head of hair."