The liberals among Democratic presidential candidates have redoubled their efforts to win still another early presidential straw poll, and the experience is embittering for Sen. Gary Hart (Colo.) and frustrating for former vice president Walter F. Mondale.

The Democrats are devoting more time than ever to fighting preelection battles in straw polls. Such samplings have begun months earlier than in the past, costing the candidates heavily in time and money.

The current contest is to win a nonbinding poll of delegates to a Wisconsin state party convention that will be held June 11.

On one level, the battle of the liberal long shots, Hart is mired in an uphill struggle against Sen. Alan Cranston (Calif.), who has out-organized and outmaneuvered him

Hart has begun to speak bitterly about what he sees as Cranston's effort to wrap his campaign around a few state straw polls. "I'm a national candidate, and he's not, yet. His is a bootstrap operation," Hart said.

On the other tier, the battle of the Democratic front-runners, Mondale is running against the Man Who Is Not There, Sen. John Glenn (Ohio), who has moved up dramatically in national opinion polls. Glenn decided to bypass Wisconsin on the grounds that a straw poll of a liberal/progressive state's convention could only jeopardize his middle-of-the-road candidacy.

Mondale hopes to score a convincing victory in Wisconsin, which has long considered the Minnesotan one of its own. But his strategists lament that his showing will not be viewed as significant with Glenn out of the race. Top state party officials supporting Mondale say that the outcome could be even worse for Mondale, contending that Cranston is within striking distance.

Mondale, Cranston and Hart upped the ante considerably here last week by adding several days of statewide campaigning.

Their strategies for the psychological warfare of the straw polls are becoming a major part of their presidential campaigns.

Mondale, as early front-runner, feels obliged to participate in all of them to demonstrate the national strength of his candidacy.

Glenn does not, and neither do the race's southern moderates, Sen. Ernest F. Hollings (S.C.) and former Florida governor Reubin Askew.

Cranston, however, has targeted his efforts one state at a time to marshal his resources. He hopes to knock Hart out of the running as the liberal alternative to Mondale, defeat Mondale in the first real contest of 1984 and finally stand alone against the more moderate Glenn.

"Mine is a 50-state strategy," Hart said, "but others go from straw poll to straw poll trying to knock me out. It won't work."

As he crossed Wisconsin last week, Hart seemed angry, his stump speech more spirited and forceful than it once was. And he emphasized at every stop that regardless of straw-poll results he will be in the race when real votes are counted in primaries and caucuses next year.

While the candidates have redoubled their efforts here, they are delivering low estimates of how much they will spend.

Hart has modestly increased his budget from $15,000 to $20,000. Cranston's managers said that they will spend $15,000, prompting Hart to say caustically: "Cut what Cranston spends here in half or two-thirds, and you'll find what I spend here. I'm not renting any buses or hotel rooms."

Hart was referring to Cranston's promise to provide hotel rooms and bus transportation from around the state for his delegates.

Hart's people said that they believe that Cranston supporters are spreading rumors, which Hart officials deny, that Hart's campaign has missed payrolls and is floundering "I'm so sick of their rumor mongering," Hart said.

At the Massachusetts state convention in April, the last straw poll in which the major candidates lavishly competed, Cranston made a strong showing, finishing ahead of Glenn and Hart although behind Mondale and a group of labor delegates who voted for "jobs" instead of a candidate.

Here, even at Hart's appearances, local party officials said that the contest is primarily between Mondale, whom they expect to win, and Cranston, who has a chance. Hart, they said, is a distant third.

Hart disagreed, saying that he expects to finish about even with Cranston or better. But Cranston said that if he finishes behind Hart, "I'd be shocked."

The difference in the appeal of the two here is that Cranston gives his liberal audiences red meat while Hart gives them white papers.

They are equally strong in their support of the nuclear-freeze movement, as is Mondale. But only Cranston has streamlined his spiel and turned his campaign into a nuclear-freeze crusade. He talks only about the freeze and the economy, which he said can be turned around by ending the arms race.

Hart gives a more detailed airing of his positions on issues. He is firmly for the freeze, but just as part of his litany of things to be done.

"Hart says the right thing about the freeze, but how deeply does he feel it?" asked Ellen Elias, a delegate from Madison. "I'm for Cranston because you can tell Cranston is truly committed to the freeze and ending the arms race. He will go all out for it."

Now, as Hart burns, Cranston basks in the glow of his fellow liberals' fire. It is good, he said, to be deemed worthy of attack.

Glenn's fade here has been strategic. "He has a previous commitment that day," a senior Glenn adviser said. Asked what it was, he responded, "It hasn't been scheduled, yet."

Behind that joke is Glenn decision not to campaign for support in straw polls that do not suit his overall strategy, a lesson learned painfully in Massachusetts.

At least a half-dozen more straw polls are scheduled before the first meaningful votes are counted in 1984. Glenn will compete in some of them, for example in Florida because he considers the South an area of strength.

Cranston, who months ago locked up the support of the Wisconsin's top liberal activists, feels secure in the knowledge that he has staked his claim with his commitment to the nuclear freeze and spent last Friday telephoning delegates to remind them of it.

He had time for this after Gov. Anthony S. Earl (D), an unabashed Mondale supporter, canceled a lunch with him and the lieutenant governor canceled dinner.

Cranston's press secretary said, "I guess the big hand of Mondale just came down from the sky and told them, 'Don't eat with the bald guy.' "