WASHINGTON -- For the first time, a major political party is on the brink of choosing an African American as its candidate for president, but when Democratic strategists and other analysts look ahead, they don't see race as Barack Obama's biggest challenge.

They worry more, they say, about other issues: Will swing voters view him as too young? Too inexperienced? Or too liberal?

"I am sure there are people in Missouri that won't vote for Barack Obama because he's black, but there are not that many of them," said Sen. Claire McCaskill (D-Mo.), a swing-state leader who endorsed Obama early. "I don't think that's going be a deal breaker."

Instead, she said, Obama's most important test should he lock up the nomination will come from Republican efforts to paint him as an elitist, a social and cultural liberal outside the mainstream of American life. "The key is going to be whether Barack can avoid getting on defense on social 'wedge' issues and can stay on the offense on economic issues," McCaskill said.

Polls suggest McCaskill may be right.

A survey released this month by the independent Pew Research Center found that most voters described Arizona Sen. John McCain, the presumptive Republican nominee, as "a centrist whose views are fairly close to their own," even though McCain describes himself as a thoroughgoing conservative. The same voters described Obama as the most liberal of the candidates still in the race, well to the left of what they saw as the midpoint of American politics.

And Obama ranked below both McCain and New York Sen. Hillary Rodham Clinton, his rival for the Democratic nomination, on the question of whether the candidate was "tough enough" to protect the nation's security.

Obama has "handicaps and potential problems, race being one of them, [but] it's not the only one," Pew Center President Andrew Kohut said. "He is perceived as a liberal. He is perceived by many voters as not well grounded on foreign policy and not tough enough . . . and he has a potential problem, distinct from race, of being seen as an elitist, an intellectual."

Taken together, that's a formidable catalog of vulnerabilities. In an ordinary election year, and with a more traditional candidate, it might make a Democratic victory hard to envision. But 2008 is not an ordinary political year: Republicans are weighted down by an unpopular incumbent, a presumed nominee who supports an unpopular war, and economic troubles that threaten voters in their homes, their jobs and their pocketbooks.

Moreover, Obama is not an ordinary candidate. An African American with an unusual life story, a liberal record and relatively little national experience, he has put together a campaign machine that has out-organized, outmaneuvered and outlasted some of the toughest, most experienced politicians in his party. And Obama has shown an exceptional ability to win over independents and draw thousands of new voters to his banner.

As a result, leaders in both parties acknowledge that much remains unknown and untested about the coming campaign. Privately, some Republican strategists say that, in contrast with the relatively familiar partisan challenge posed by Clinton, the level of uncertainty is so high with Obama that they can envision him winning in a landslide -- or losing by a similar margin.

And Mitch Ceasar, chairman of the Broward County Democratic Party, said party strategists aren't sure how Obama's unusual background will play there. "This is a political generational change, both in terms of the candidate definition and the groups to which he appeals," Ceasar said.

Obama acknowledges potential vulnerabilities, but he and his strategists believe those would be overshadowed in the general election campaign by economic and other issues.

"Every candidate has strengths and weaknesses," Obama said Saturday at a news conference in Bend, Ore. "I no doubt have weaknesses, but I think I have enormous strengths as well. And in a contest between myself and John McCain . . . I think this is going to be a very concrete contest around very specific plans for how we improve the lives of Americans."

To a significant degree, the focal point of Obama's challenge appears to be white working-class voters.

In a Los Angeles Times/Bloomberg poll released Friday, voters as a whole said they preferred Obama over McCain by 46% to 40%, with 9% undecided. Among white voters, however, McCain outpolled Obama by 45% to 41%. Obama's strong support among black voters helped account for his overall plurality.

Obama's deficit among white voters is not unusual for Democratic candidates. In 2004 and 2000, Democrats John F. Kerry and Al Gore both lost the white vote to George W. Bush by wide margins, but the overall results were much closer. Indeed, Gore narrowly won the popular vote, and lost the White House only after litigation over the electoral vote.

"The white working class has gone to the Republican nominee for many elections, going back even to the Clinton years," Obama strategist David Axelrod told National Public Radio on April 23, after his candidate lost the Pennsylvania primary to Hillary Clinton. "This is not new that Democratic candidates don't rely solely on those votes."

Still, Obama strategists acknowledge that one of their first tasks is reaching out to the Democrats who tended to vote for Clinton in Pennsylvania and other battleground states such as Ohio, Missouri and Florida: not only blue-collar, downscale white voters, but also older voters, Latinos and Jews.

This month, Obama plans to spend three days in Miami and the Tampa Bay area.