Several hundred residents of this economically ailing industrial city applauded enthusiastically in the winter chill of a small park today as their presidential candidate harshly criticized the politicians who guided this nation to independence and then tightly controlled its public life.

The war in neighboring Bosnia was a mistake, the candidate, Stipe Mesic, told them. Croatian politicians stole millions of dollars from the people, he continued. Croats who live in Bosnia should get off Croatia's dole and stand on their own feet. The government should cooperate with international war crimes probes and stop suffering for the atrocities committed by its soldiers.

Such political heresy was rarely heard here under the authoritarian rule of Franjo Tudjman. Few here expected such a warm reception for it so soon after Tudjman's death last month. But these blunt criticisms by Mesic, a former president of the Croatian parliament, have suddenly propelled him into the frontrunner's position heading into Monday's first round of the election to choose Tudjman's successor.

Competing without major backing from any political party and courting voters with a series of wildly popular cafe chats, Mesic, 65, is promising nothing less than a political revolution.

He says he favors fast-track membership for Croatia in NATO and the European Union, an end to sweetheart deals for the politically powerful, a cutoff of funding for Croat soldiers in Bosnia and a return to the public treasury of all funds taken by the leaders of what people here describe as Tudjman's "kleptocracy."

His candidacy poses a risk to the powerful, producing at least one concrete threat of physical harm--from hard-line Croat nationalists based in Canada, Mesic says. But in the topsy-turvy politics of the post-Tudjman era, his crowds are growing rapidly and his support is already estimated at 10 percentage points higher than his nearest rival, Drazen Budisa, 51, a technocrat and former librarian.

Although his victory is by no means assured--particularly on the first ballot--Mesic's avid support by at least a third of the potential voters questioned in recent polls has already proven that a decade of nationalist rhetoric and highly concentrated authority have left a bitter aftertaste.

Widespread economic woes and resentment of corruption helped defeat Tudjman's party, the Croatian Democratic Union, in parliamentary elections on Jan. 3. Legislative control was passed to a coalition of the center-left Social Democratic and Social Liberal parties.

But Mesic proudly reminds voters he belongs to neither one, and admits he favors a more radical agenda than their leaders have embraced. In contrast, those with the most conservative views--including two senior army officers and a rightist politician whose supporters wear black shirts--have each gained only negligible support.

Polls indicate that Mate Granic, the candidate of the former ruling party and an ex-favorite of the Clinton administration, is supported by just 15 percent of the public. Evidently aware of his dim prospects of gaining the 51 percent of the vote needed for election, he said in an interview Thursday that "it was a mistake for me, a month ago, not to run as an independent."

Tudjman's name has scarsely been mentioned in the campaign--many citizens say his legacy was buried at his Dec. 13 state funeral--but Mesic has prospered by campaigning as the former president's implicit opposite. Where Tudjman brooked no dissent and centralized power in the presidency, Mesic says he favors a decentralization of state power. Where Tudjman loved ceremony and pomp, Mesic's campaign advertisements ask, "Fancy a coffee with the president? Let's go."

With bushy black eyebrows, a close-cropped beard and a bristle haircut, Mesic appears more avuncular and jolly than most of his eight opponents. Where Budisa--whose support is hovering at 23 percent--bills himself as the most "reliable, serious, and educated" candidate and presses a detailed, 14-point reform platform, Mesic speaks in broad terms, gently waves his hands, and swats away criticism with irreverent humor. He says he is proud of driving a four-year-old Volkswagen Golf and promises his net worth won't be any greater after he leaves office.

"He is amiable, nonchalant, and has a good sense of humor, but he is not well-defined," complained Jozo Rados, the vice-president of Budisa's party. "We expected an easier victory . . . [and were] surprised that such a populist campaign met with such approval."

Mesic has sought to position himself with average citizens who were left behind while Tudjman's cronies got rich. He stresses the need for Croatia's integration with the West and has reiterated his desire to be the "president of all Croatian citizens"--a phrase meant to include its ethnic minorities.

He has called for a full accounting of Croatia's past financial assistance to the dwindling number of Croats who remain in Bosnia, an unlisted budget expenditure estimated at roughly $1 million a day. He says that some of these funds wound up being laundered in Caribbean banks before being privately reinvested in Croatian businesses, and promised to seek international help in tracking the funds.

"I'm certain that many people will be brought before courts," he promised viewers of a nationally televised debate tonight. "Croatia will be internationally developed because it will become a state of law."

Besides disagreeing about the wisdom of a cutoff of Croatian aid to ethnic Croats in Bosnia, Mesic and Budisa have said they differ primarily on the degree to which Croatia should cooperate with the international war crimes tribunal probe of Croatian military atrocities during the 1991-95 Bosnian war.