IEV, Ukraine, Dec. 4 - Viktor A. Yushchenko, the opposition candidate who is trying to remake Ukraine through a sweeping change of power, stood on the stage in Independence Square here and surveyed the rapt crowd during one of his many appearances in two weeks of political crisis. His face, from chin to forehead, was a darkened mask of cysts. Its ugliness was unsettling.

"Do you like my face?" he asked, his voice passing through the huge speakers spread around the square. "This is the face of today's Ukraine."

Mr. Yushchenko is now surging, the leading candidate in a second presidential runoff that Ukraine's Supreme Court ordered because last month's was tainted by government fraud.

A former prime minister and head of Ukraine's central bank, he has seized the reform agenda in the battle against the incumbent government of the departing president, Leonid D. Kuchma.

Riding a wave of anti-Kuchma public sentiment, Mr. Yushchenko's message rests partly on the sustained exposure of what he calls the current government's ills. Many Ukrainians believe that Mr. Yushchenko is their best hope for changing the way the country has been ruled since Soviet times.

In this battle for public perception, Mr. Yushchenko's face is one of his weapons. Mr. Yushchenko said his recent disfiguration was a result of his being poisoned. Mr. Kuchma's camp says that he is afflicted by a mysterious disease, or that perhaps he ate bad sushi. But the illness underscores Mr. Yushchenko's message that in Ukraine, things are so fundamentally ugly that they must fundamentally change.

Mr. Kuchma's government, the opposition leader says, is shadowy, thuggish and corrupt, most recently expressed in its effort to force its choice for president, Prime Minister Viktor F. Yanukovich, into power. It remains rooted in a mix of post-Soviet centralization, economic banditry and an embarrassing subservience to Vladimir V. Putin, Russia's president. It is, as Mr. Yushchenko called it Friday night, "a colossus on clay legs."

His administration, Mr. Yushchenko says, would be organized around ideas central to civil society: honesty, transparency, democracy and fairness. It would also nudge Ukraine toward the global world, expanding trade with Europe and urging the Ukrainian use of Western languages, all while seeking to unify a country that throughout the campaign has shown signs of an organic political split.

These are his positions. A question follows him. If he succeeds in toppling the current political clan, can he deliver on his promises?

Mr. Yushchenko's background is of a man who has lived in both the Soviet and Western worlds, and spent a great deal of his energy examining their economic models and links.

Mr. Yushchenko, 50, was born in a family of teachers in northeastern Ukraine, and began his career as an economist in a regional affiliate of the Soviet Union's state bank. He later held a series of bank management posts in Kiev, the Ukraine capital, in the Soviet Union's final years.

In 1993, two years after Ukraine broke from the Soviet Union, he was appointed head of the nation's central bank, a post he held until he became prime minister in 1999.

During his years at the bank, he was involved in steering Ukraine from Communism to a market economy, developing monetary and credit policies, and introducing the hryvnia, Ukraine's currency.

Ukraine is not a country known for its public integrity, and yet, in spite of his rival campaign's efforts to explore his past and smear him, Mr. Yushchenko has managed to navigate the intersection of Ukrainian government and business without a major or enduring scandal.

His reputation is clean enough that his opponents sometimes sneeringly refer to him as "the messiah."

His period as Mr. Kuchma's prime minister was short-lived and marred both by infighting in Parliament and what seemed his sense of powerlessness. Under the current Ukrainian Constitution, real power lies in the presidency.

In 2001, less than two years after Mr. Yushchenko assumed the post, as a potential protégé, Mr. Kuchma orchestrated a no-confidence vote against him, and those who had worked with him were forced to choose sides.

Mr. Yushchenko left office, vowing to return. It was a clear sign that he would try the opposition route, even though, not long before he lost his post he had said on Ukrainian television, referring to Mr. Kuchma, "I think that our relations are similar to those between a father and a son."

Some of the splits were bitter. Oleksandra Kuzhel, who worked for Mr. Yushchenko when he was prime minister and was one of the Yanukovich administration's liaisons to business, said Mr. Yushchenko had some of the worst characteristics of politicians, thinking more of his image and politics than of his government duties.

Some days, she said, he was more likely to go to political events than government meetings, and was chronically late.

"He is a good man, but he's not a manager," she said. "He does not plan his next day. He does not live up to his promises. He does not control the work he has set out before him. This is a death sentence for a business manager."

Such descriptions of him are of a type. Having assumed the role as foil to Mr. Kuchma, whose popularity in much of Ukraine has sunk, Mr. Yushchenko's own popularity has risen, as the government's efforts to demonize him have grown.

The state-run news media, or media owned by his rivals, have portrayed him as a radical and nationalist, and questioned whether his marriage to Kateryna Chumechenko, a Ukrainian-American who once worked in the State Department, has put him under the sway of the United States.

The bad press has not stopped him, and in a style of politicking reminiscent of campaigns in the West, he has reached out to almost all classes of voters, promising bold, instant change.

On Thursday night, addressing supporters in Independence Square, he appealed to Ukrainian history and his own roots in a small village on the border with Russia. He collects and restores rustic Ukrainian artifacts and relics from the country's ancient past. He keeps a house outside of Kiev, as his father and grandfather did.

For all his charisma on the stump, however, he can display stubbornness, a trait his opponents criticized again on Saturday as wrangling over the new election continued. He refused to follow the advice of doctors treating his mysterious ailment in Austria, and returned to campaigning in October with a catheter in his back to feed him painkillers.

He has campaigned partly by promising that as president he would immediately sign 11 decrees that would, among other things, fight public corruption, require local governments to make public reports of their activities, reduce the activities of the tax inspectors and accelerate withdrawal of Ukraine's soldiers in Iraq.

Those decrees could begin to nudge Ukrainian government away from its reputation as a gangster state. One includes a requirement for senior public officials to declare all income and expenditures and another would bar government employees from accepting gifts worth more than about $18.

His platform offers promises to almost every class of voter.

For young men, there is a pledge to cut the term of military conscription to 12 months from 18, and then, in 2010, to do away with it altogether. For young women there is a pledge to increase financial assistance at childbirth by a factor of 10. For those who lost savings during the runaway inflation of the 1990's, he included a promise to reimburse them, in part through trying to undo a privatization deal Mr. Kuchma made this year.

Those in the opposition camp say he may have one weakness: Aside from the unifying cause of ousting Mr. Kuchma, Mr. Yushchenko has few issues that can bind his various blocs of supporters.

His coalition is a mix of very different interests. They include students who seek revolutionary and absolute change; his own oligarchs, who are in part engaged in competition with the Mr. Kuchma's money clans, and who might seek protection or favors should Mr. Yushchenko become president; a raft of medium-size businesses that want law and agencies more favorable to their growth; and politicians in his camp who expect him to divide the president's powers with Parliament, and introduce a new degree of balance in Ukrainian political life.

As Mr. Yushchenko enters his next campaign, he will have to continue to navigate these sometimes conflicting pulls, which are, for now, largely quiet in the din of political battle against Mr. Kuchma.

Ms. Kuzhel, speaking before the momentum clearly shifted toward the opposition, called its base "a situational majority," which she defined as "a lot of people who use an image to get together to take power."

She also said no matter what his stature in Kiev and western Ukraine might be, Mr. Yushchenko's appeal had not been universal, and much of the country was against him, most notably the industrial interests in eastern Ukraine.

"I would like to remind you," she said, "that these people produce more than half of Ukraine's G.D.P."