All told, 59 percent of voters surveyed said Ms. Palin was not prepared for the job, up nine percentage points since the beginning of the month. Nearly a third of voters polled said the vice-presidential selection would be a major factor influencing their vote for president, and those voters broadly favor Senator Barack Obama, the Democratic nominee.

And in a possible indication the choice of Ms. Palin has hurt Mr. McCain’s image, voters said they had much more confidence in Mr. Obama to pick qualified people for his administration than they did in Mr. McCain.

After nearly two years of campaigning, a pair of hotly contested nominating battles, a series of debates and an avalanche of advertisements, the nationwide poll found the contours of the race hardening in the last days before the election on Tuesday. Twelve percent of the voters surveyed said they had already voted. These were among the findings:

Mr. Obama is maintaining his lead, with 51 percent of likely voters supporting him and 40 percent supporting Mr. McCain in a head-to-head matchup.

Some perceptions of race are changing, with a marked increase in the number of people who say they believe that white and black people have an equal chance of getting ahead in America today.

Mr. McCain’s focus on taxes, including his talk about Joe the Plumber, seems to be having some effect, as a growing number of voters now say Mr. McCain would not raise their taxes.

Eighty-nine percent of people view the economy negatively, and 85 percent think the country is on the wrong track.

Mr. Obama continues to have a significant advantage on key issues like the economy, health care and the war in Iraq.

The survey found that opinions of Mr. Obama and Mr. McCain had hardened considerably, as 9 out of 10 voters who said they had settled on a candidate said their minds were made up, and a growing number of them called it “extremely important” that their candidate win the election. Roughly half of each candidate’s supporters said they were “scared” of what the other candidate would do if elected. Just 4 percent of voters were undecided, and when they were pressed to say whom they leaned toward, the shape of the race remained essentially the same.

Bolstered by the fiscal crisis and deep concerns about the direction of the country, Mr. Obama has seemed to solidify the support he has gained in recent months. When likely voters were asked whom they would vote for in an expanded field that included several third-party candidates, Mr. Obama got the support of 52 percent of them, Mr. McCain 39 percent, Bob Barr 1 percent, and Ralph Nader 2 percent.

The nationwide telephone poll was conducted Saturday through Wednesday with 1,439 adults nationwide, including 1,308 registered voters. The margin of sampling error is plus or minus three percentage points.

The poll was conducted as a wide range of state polls have shown Mr. Obama, of Illinois, ahead or tied in several crucial contested states, including some traditionally Republican states that Mr. McCain, of Arizona, must carry to win the election.

The survey suggested that Mr. Obama’s candidacy — if elected, he would be the first black president — has changed some perceptions of race in America. Nearly two-thirds of those polled said whites and blacks have an equal chance of getting ahead in today’s society, up from the half who said they thought so in July. And while 14 percent still said most people they knew would not vote for a black presidential candidate, the number has dropped considerably since the campaign began.

Mr. McCain’s heavy focus on taxes in the final weeks of the campaign seems to be having some effect, the poll found.

Forty-seven percent of voters said Mr. McCain would not raise taxes on people like them, up from just 38 percent who said so two weeks ago. (And 50 percent said they thought Mr. Obama would raise taxes on people like them, while 44 percent said he would not; both numbers are similar to two weeks ago.)

With just days until Americans choose a new president, the survey found them deeply uneasy about the state of their country. Eight-five percent of respondents said the country was pretty seriously off on the wrong track, near the record high recorded earlier this month. A majority said the United States should have stayed out of Iraq. And President Bush’s approval rating remains at 22 percent, tied for the lowest presidential approval rating on record (which was President Harry S. Truman’s rating, recorded by the Gallup Poll in 1952).

Mr. McCain’s renewed efforts to cast himself as the candidate of change have apparently faltered. Sixty-four percent of voters polled said Mr. Obama would bring about real change if elected, while only 39 percent said Mr. McCain would. And despite Mr. McCain’s increased efforts to distance himself from President Bush, a majority still said he would generally continue Mr. Bush’s policies.

Dixie Cromwell, a 36-year-old cosmetologist from Shelby, N.C., who is a Republican, said in a follow-up interview that she had already voted for Mr. Obama.

“I generally vote Republican, but this year I voted Democrat,” she said. “I just don’t feel we can go through any more of the same old thing that we’ve been going through with the Republican Party.”

Mr. Obama’s policies were seen as much more likely to improve the economy, provide health insurance to more people, and scale back military involvement in Iraq than Mr. McCain’s were. But Mr. McCain enjoyed an advantage when it came to questions about which candidate would make a better commander in chief: 47 percent of voters said Mr. McCain was very likely to be an effective commander in chief, compared with 33 percent who said Mr. Obama would be.

While a majority viewed Ms. Palin as unqualified for the vice presidency, roughly three-quarters of voters saw Mr. Obama’s running mate, Senator Joseph R. Biden Jr. of Delaware, as qualified for the job. The increase in the number of voters who said Ms. Palin was not prepared was driven almost entirely by Republicans and independents.

Over all, views of Ms. Palin were apparently shaped more by ideology and party than by gender. Ms. Palin was viewed as unprepared for the job by about 6 in 10 men and women alike. But 8 in 10 Democrats viewed her as unprepared, as well as more than 6 in 10 independents and 3 in 10 Republicans.