WASHINGTON — Mayor Giuliani’s lead over his Republican presidential rivals has narrowed considerably, while Senator Clinton of New York has maintained her advantage in the race for the Democratic nomination, according to a new Washington Post-ABC News poll.

Arizona’s Senator McCain, whose candidacy has been buffeted by lackluster fundraising and his embrace of President Bush’s troop surge policy in Iraq, runs a solid second in the GOP nominating contest. But there is fresh evidence in the new survey that his focus on the war and on attracting conservative support have made him more polarizing as a potential general election candidate.

Mr. Giuliani remained the frontrunner in the national poll, but his support has eroded. In a late February Post-ABC News poll, 44% of Republicans and Republican-leaning independents preferred Mr. Giuliani for the nomination, a figure now down to 33%. Support for Mr. McCain held steady at 21%.

Mr. Giuliani’s support dipped in part because of the possible entry of a former Tennessee senator, Fred Thompson, into the Republican race. Mr. Thompson ran third in this poll, with 9%, tying him with a former Massachusetts governor, Mitt Romney.

A former House speaker, Newt Gingrich, who has said he will decide this fall whether to become a candidate, ran fifth at 6%, down from 15% in February. No other Republican candidate received more than 2% in the current poll.

Among Democrats, Mrs. Clinton led in the survey with 37% support to Illinois’s Senator Obama’s 20%. Vice President Gore, who has said he has no plans to run, had the support of 17% of Democrats and Democratic-leaning independents; a former North Carolina senator, John Edwards, stood at 14%. No other Democrat received more than 3%.

In late February, Mrs. Clinton led with 36% to Mr. Obama’s 24%. Over those two months, Mr. Obama has not been able to maintain the momentum he had shown in attracting black support. In the new poll, 43% of blacks preferred Mrs. Clinton for the Democratic nomination while 34% preferred Mr. Obama.

Democrats remained far more satisfied with their field of candidates than did Republicans. Fully 80% of Democrats said they were either very or somewhat satisfied with their choices, compared to just 65% of Republicans. Republican unrest has only increased in the past two months, providing a push to Mr. Thompson’s possible candidacy.

Beyond the primaries, the survey paints the portrait of an electorate still evenly and deeply divided. Four of the six major candidates — Mrs. Clinton and Messrs. McCain, Giuliani, and Romney — are considered unacceptable by at least 40% of all Americans.

Mrs. Clinton long has been a polarizing figure, and the latest survey found that 45% of Americans — and 51% of all independents — said they definitely would not support her in November 2008 if she were to become the Democratic nominee.

That is somewhat offset by the fact that she attracts more definite supporters than any of the other leading candidates. In the poll, 27% said they would definitely support her, up from 19% last May.

Mr. McCain by contrast has become significantly less acceptable as a general election candidate over that time. A year ago, 28% of Americans said they “definitely would not vote” for him if he were to become the Republican nominee; in this poll that number soared to 47%.

Since last May, Mr. McCain has shored up some GOP support but lost a significant amount of his crossover appeal: The percentage of independents saying they definitely would not vote for him jumped from 25% to 41% in the current survey. The number of Democrats who said they would not support him under any circumstances leapt from 38% in May to 68%.

Although Mr. Romney is not as well known nationally as many of the other leading candidates, he has made a poor first impression on the public. Fifty-four percent said they definitely would not vote for him, and just 7% said they definitely would back him if he wins the GOP nomination.

The GOP race continues to show considerable volatility. Mr. Giuliani’s surge earlier in the year first highlighted Mr. McCain’s problems. But the former mayor is out of step with socially conservative Republicans, and his rapid rise has been followed by what has clearly become a period of settling. Over the past two months, Mr. Giuliani lost support among women, white evangelical Protestants, those over age 45 and veterans.

Among Republicans who call themselves socially conservative, Messrs. Giuliani and McCain run about evenly (21% to 20%), but among the party’s smaller socially moderate wing, Mr. Giuliani enjoyed a wide lead.

Eight years ago, Mr. McCain was highly popular with independent voters, but the latest survey showed Mr. Giuliani with a significant lead among Republican-leaning independents (36% to 14%). Among Republicans, 31% supported Mr. Giuliani and 25% preferred Mr. McCain.

Two questions in the new poll related to the news that Mr. Edwards’s wife, Elizabeth, has had a recurrence of her breast cancer and the disclosure by Mr. Thompson that he was diagnosed with lymphoma two-and-a-half years ago; his cancer is now in remission.

Nearly nine in 10 people said the fact that someone has been treated for cancer and the disease is in remission would make no difference whether to support or oppose a particular candidate.

Among Democrats, more than nine in 10 said Elizabeth Edwards’s latest diagnosis would have no impact on their choice in the nomination battle. The couple’s decision to continue Mr. Edwards’s campaign for the nomination drew strong support: Three in four Democrats said that decision was the right thing to do.

The Post-ABC News poll was conducted by telephone April 12–15 among a random sample of 1,141 adults, including an oversample of African Americans, for a total of 206 black respondents. Results from the full sample have a margin of error of plus or minus 3%. The margin of error among the Republican sub-sample is plus or minus 5 points and among the subsample of Democrats it is plus or minus 4 points.