Among Republicans, former New York mayor Rudy Giuliani maintained a 14-point lead over Arizona Sen. John McCain.

Clinton is the only contender in either party to show movement outside the poll's margin of error. She is the choice of 38% of the Democrats and Democratic-leaning voters surveyed, up 7 points from a survey taken three weeks earlier. Obama is at 23%, 3 points lower than before.

Giuliani is supported by 34% of the Republicans and Republican-leaning voters surveyed, compared with 20% for McCain.

Charles Franklin, a political scientist at the University of Wisconsin at Madison who studies polling, cautions against making too much of shifts in national surveys 18 months before the election.

"You should expect a fair bit of bouncing around," Franklin says. He notes that debates at this point are being watched mostly by party activists and political junkies: "They're not real likely to show up in an effect on voters as a whole unless a candidate makes some horrible mistake."

Still, Clinton strategist Mark Penn attributes her boost in the poll to her performance in the opening April 26 debate.

"At the debate people got the first chance to see them all side-by-side," Penn says, "and I think she is looking very ready to lead."

The survey of 1,010 adults was taken Friday through Sunday.

The USA TODAY survey shows yearning in both parties for people who aren't running, at least not yet. Former vice president Al Gore is the first choice of 14% of Democrats, ahead of every candidate in the field except Clinton and Obama.

Among Republicans, former Tennessee senator Fred Thompson finishes third at 13%; former House speaker Newt Gingrich is fourth at 8%. Neither is now a candidate.

If the GOP choice comes down to Giuliani or McCain, Republicans and Republican-leaning voters chose the former New York mayor, 56%-38%.

Democrats and Democratic-leaning voters chose Clinton over Obama, 56%-37%.

Asked an open-ended question about why they support one or the other, 35% of Clinton's backers cite her experience; 23% favor her positions on issues; 17% like the fact that she is a woman. Ten percent mention her husband, former president Bill Clinton.

Obama has become the candidate of choice for those with concerns about the frontrunner.

Among his supporters, 37% say either that they don't like Clinton, that she has "too much baggage" or that she is more polarizing than he is. Another 10% say he has a better chance of being elected president. Three percent of Clinton's supporters say they support her because she has a better chance of being elected.

The survey's margin of error for the samples of 427 Republican and Republican-leaning voters and 491 Democrats or Democratic-leaning voters is 5 percentage points. For the full sample, it is +/—3 points.

In the poll, President Bush's job-approval rating continues to be in the doldrums, at 34%.

He has entered his eighth month below 40% approval — the longest stretch of such dismal ratings for any modern president except Harry Truman during the Korean War and Richard Nixon during the Watergate scandal.