WASHINGTON — As Sen. Barack Obama opens his campaign as the first African-American on a major party presidential ticket, nearly half of all Americans say race relations in the country are in bad shape and three in 10 acknowledge feelings of racial prejudice, according to a new Washington Post-ABC News poll.

Lingering racial bias affects the public's assessments of the Democrat from Illinois, but offsetting advantages and Sen. John McCain's age could be bigger factors in determining the next occupant of the White House.

Overall, 51 percent call the current state of race relations "excellent" or "good," about the same as said so five years ago. That is a relative thaw from more negative ratings in the 1990s, but the gap between whites and blacks on the issue is now the widest it has been in polls dating to early 1992.

More than six in 10 African-Americans now rate race relations as "not so good" or "poor," while 53 percent of whites hold more positive views. Opinions are also divided along racial lines, though less so, on whether blacks face discrimination. There is more similarity on feelings of personal racial prejudice: Thirty percent of whites and 34 percent of blacks admit such sentiments.

At the same time, there is an overwhelming public openness to the idea of electing an African-American to the presidency. In a Post-ABC News poll last month, nearly nine in 10 whites said they would be comfortable with a black president. While fewer whites, about two-thirds, said they would be "entirely comfortable" with it, that was more than double the percentage of all adults who said they would be so at ease with someone entering office for the first time at age 72, which McCain, R-Ariz., would do should he prevail in November.

Even so, just over half of whites in the new poll called Obama a "risky" choice for the White House, while two-thirds said McCain is a "safe" pick. Forty-three percent of whites said Obama has sufficient experience to serve effectively as president, and about two in 10 worry he would overrepresent the interests of African-Americans.

Obama will be forced to confront these views as he seeks to broaden his appeal. He leads in the Post-ABC poll by six percentage points among all adults, but among those who are most likely to vote, the contest is a toss-up, with McCain at 48 percent and Obama at 47 percent.

Many think Obama has the potential to transform current racial politics. Nearly six in 10 believe his candidacy will shake up the racial status quo, for better or worse. And by nearly 3 to 1, those who think Obama's candidacy will affect race relations said it will have a positive impact.

But sorting out the impact of these and other racial attitudes on the presidential election is not straightforward.

About a fifth of whites said a candidate's race is important in determining their vote, but Obama does no worse among those who said so than among those who called it a small factor or no factor.

Nor are whites who said they have at least some feelings of racial prejudice more or less apt to support Obama than those who profess no such feelings.

Putting several measures together into a "racial sensitivity index" reveals that these attitudes have a significant impact on vote preferences, independent of partisan identification. Combining answers to questions about racist feelings, perceptions of discrimination and whether the respondent has a close personal friend of another race into a three-part scale shows the importance of underlying racial attitudes.

Whites in the top sensitivity group broke for Obama by nearly 20 percentage points, while those in the lowest of the three categories went for McCain by almost 2 to 1.

A similar pattern holds among Democrats. Obama scores more than 20 points better among nonblack Democrats and Democratic-leaning independents in the "high" group than he does among those in the "low" group.

Obama has some convincing to do among the 29 percent of whites who fall into the scale's lowest category. Almost six in 10 whites in the low-sensitivity group see him as a risky choice, and a similar percentage said they know little or nothing about where he stands on specific issues. Nearly half do not think his candidacy will alter race relations in the country; 20 percent think it will probably make race relations worse.

But McCain's challenges are also an important part of the equation. Numerous polls, for example, have indicated that McCain's age may be a bigger detractor than Obama's race. And more are now concerned that McCain will heed too closely the interests of large corporations than said so about Obama and the interests of blacks.

The poll was conducted by phone June 12 through 15 among a national random sample of 1,125 adults. The results from the full poll have a margin of sampling error of plus or minus three percentage points. The error margin is larger for subgroups; it is four points among whites and seven points among African-Americans.