WASHINGTON — When Elaine Ellis began her rounds as a New York nursing assistant one morning this spring, she had an improbable companion: John Edwards, the Democratic presidential candidate, who had accepted a union invitation to spend the day with a low-wage worker.

When Ohio steelworkers went on strike last fall to protest a plant closing, who joined their rally? John Edwards.

Next month, low-income survivors of Hurricane Katrina will have another visit from Mr. Edwards, who announced his presidential campaign amid the storm rubble of New Orleans.

For more than two years, Mr. Edwards has been building his campaign for the Democratic presidential nomination around an issue long shunned by leading candidates: the plight of the poor and working class. He has backed his public appearances with unusually detailed proposals to provide universal health care, raise taxes on the rich, and eliminate poverty over the next 30 years.

“This is a huge moral issue facing the country,” Mr. Edwards said in a telephone interview as he headed into a Memorial Day weekend campaign swing through Iowa. “I don’t see in polls that it is a driving issue [for voters], but it is for me.”

In adopting poverty and low-wage work as his themes, Mr. Edwards has struck a far more combative, populist tone than in his 2004 presidential campaign. And that has helped him elbow into the top tier of a field dominated by better-financed candidates Senators Clinton and Obama — and even has boosted him to a lead in polls in the early voting state of Iowa.

But Mr. Edwards’s 2008 strategy carries significant risks, in part because it speaks most directly to a slice of the electorate that has notably little political clout. Some analysts warn that an agenda that smacks of class warfare risks alienating middle-class swing voters and moderate Democrats who do not want to revive criticisms that theirs is the party of the poor and welfare recipients.

“It is very brave to take on an issue that he himself says has no constituency that has power, but it’s a tough road to be trodding to the White House,” said Matt Bennett, a vice president of Third Way, a centrist Democratic research organization.

Still, the centrist drift of President Clinton’s presidency, with its emphasis on reining in welfare and helping the middle class, has left many activists and liberals hungry for a return to the party’s traditional commitment to the disadvantaged.

“That appeals to Iowa Democrats,” said a former Iowa party chairman, Gordon Fischer, who is not affiliated with any candidate. “It’s the kind of throwback that appeals to traditional Democratic values.”

But Mr. Edwards’s focus on the disenfranchised also has left him open to a cascade of controversies that threaten to cast him as a hypocrite. Wealthy from his career as a lawyer, Mr. Edwards has been pummeled by reports that he has spent $400 for a haircut, built himself a 28,000-square-foot mansion on a 100-acre estate, and did consulting work for a hedge fund that traffics in offshore investing of the sort Mr. Edwards has criticized.

“It has hurt him, and I say that as someone who admires and respects John Edwards a tremendous amount,” Mr. Fischer said.

Mr. Edwards argues that being well off does not disqualify him from being an effective advocate for the have-nots of the world. He points to his roots in a family of modest means.

“I haven’t forgotten where I came from,” he said in the interview. “I came from nothing and have been successful. Most people think that’s a good thing.”

Mr. Edwards’s up-by-the-bootstraps life story was a central part of his campaign for the presidency in 2004, as well as of stump speeches after he was named Senator Kerry’s running mate. The son of a mill worker, Mr. Edwards grew up in a tiny North Carolina town and was the first in his family to go to college. He went on to law school and in time made millions, largely by representing plaintiffs in lawsuits against big companies.

His 2004 campaign had an element of populism, with its critique of a nation split into “Two Americas,” one for the rich and the other for ordinary people. But his tone was more cautious than today, and his image was one of a Southern centrist.

In the years after he and Mr. Kerry lost the 2004 election, Mr. Edwards has labored to establish himself as a champion of the disenfranchised. He established a research center on poverty at the University of North Carolina, which gave him a platform for speaking to important Democratic constituencies around the country.

“The poverty center was a significant piece of infrastructure that kept him in the national dialogue,” said Ferrel Guillory, an expert on Southern politics at the University of North Carolina.

Mr. Edwards also spent much of the past three years building bridges to organized labor. He campaigned in six states for 2006 ballot initiatives to increase the minimum wage, and he traveled to help labor-organizing campaigns for janitors and hotel workers. He won an AFL-CIO award for making big contributions to the labor movement.

It remains to be seen, however, if his heavy bet on labor will pay off in securing formal endorsements. The AFL-CIO and other big unions often hold off on making endorsements until the likely nominee becomes clear. In 2004, UNITEHERE, the union of textile and hotel workers, was the only union to back Mr. Edwards.

Mr. Edwards also has developed a detailed anti-poverty agenda that he hopes will cast him as the candidate of big ideas.

“What I am offering are very clear, bold policy initiatives that I think the country needs,” he said in the interview. “I don’t think small, incremental steps are enough.”

It is not clear that Mr. Edwards’s message is reaching far beyond the political elite and activist core: In a recent poll by the Pew Research Center, people regarded Mr. Edwards as the most conservative candidate in the Democratic field. And while Mr. Edwards is connecting with labor activists, he does not appear to be catching on among minorities who might seem like a natural constituency: A recent Los Angeles Times/Bloomberg poll found that most blacks supported Mrs. Clinton or Mr. Obama, with only negligible support among blacks for Mr. Edwards.

The broader political challenge in championing a new war on poverty is that middle- and upper-class voters might not see it as relevant to their lives. But Mr. Edwards also has initiatives aimed at the economic insecurity reaching further up the income ladder, such as his plan for universal health insurance.

“Most people do think of themselves as middle class — especially the people who vote — while the poor are a minority,” said Ruy Teixeira, a policy analyst at the Center for American Progress, a liberal think tank. “Health insurance is a good way of welding together the poor and middle class and doing something for both at the same time.”

Mr. Edwards’s message of economic populism and strident opposition to the Iraq war may not become popular everywhere, but it seems to be working in Iowa, where he is leading in many polls. “Mr. Edwards is the perfect Iowa candidate,” said William Galston, a former adviser to President Clinton. “But if he cannot win Iowa, he is dead.”