The races for both parties' presidential nominations are showing signs of tightening. Yet a closer look at the numbers also reveals intriguing crosscurrents that raise questions about how solid the presumed Democratic advantage may be in November 2008.

Surveys show that people would clearly prefer that the Democratic Party win the White House next year, which political operatives and analysts attribute to the deep unpopularity of President Bush and the war in Iraq and a broad desire for change.

When top Republican and Democratic candidates are paired, however, the Republican hopefuls generally do quite well or at least hold their own.

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Next year's Election Day is eons away in political time, and many things could happen to alter today's dynamics. For now, the surveys raise questions about whether the apparent Democratic edge would really hold up should Republican candidates with moderate credentials like Rudy Giuliani or John McCain face Democrats such as Hillary Rodham Clinton or Barack Obama.

When people are asked which party they want to capture the White House, "They tell you about the general climate or mood, and that's not good for Republicans," said Whit Ayres, a Republican pollster not working for a presidential candidate.

"It's almost a 'Do you want George Bush to be president again?' question," he said. "But it's not the case if you say, 'Do you want Hillary Clinton or Rudy Giuliani to be president?"'

For now, Giuliani, the former New York City mayor, remains atop his Republican presidential rivals while New York Sen. Clinton leads the Democratic field. But with few voters focusing yet on those races and a long way to go, their standings are vulnerable and may be eroding already.

Early polls are important, not as predictors of who will prevail but because strong showings make it easier for candidates to attract contributors, campaign supporters and media coverage.

"Voters are still going through the sorting out process," said Geoffrey Garin, a Democratic pollster not aligned with any candidate. "The opinions voters express are not at all inconsequential, but neither are they necessarily very permanent."

For months, Clinton has enjoyed a healthy lead over her closest competitor, Obama, the Illinois senator, leading him in some polls by 2-to-1 margins or more.

Late last month, an NBC News-Wall Street Journal poll showed her advantage shrinking to 5 percentage points. A USA Today-Gallup survey in mid-April showed her with the same edge, while another by CNN-Opinion Research Corp. showed her lead dipping to 4 points.

But the soundings were unclear. The NBC-Journal poll was a drop from a 12-point Clinton advantage in March, but the change was within the sampling margin of error, meaning it didn't necessarily reflect an actual shift in voters' sentiments.

At the same time, other national polls by Newsweek, the nonpartisan Pew Research Center, Quinnipiac University and others showed either a wider lead for Clinton or little recent change.

The results have been similarly mixed on the Republican side.

Giuliani's lead over McCain fell to 15 points in a Newsweek poll earlier this month, and to 8 points in a Quinnipiac University survey. Other polls showed him with a steady or larger advantage.

"It's very early and very fluid," said Ed Gillespie, a lobbyist and former Republican Party chairman. "I think you'll see a lot of fluctuation between now and January."

That is when the first party primaries and caucuses will begin, though some states are still considering moving up their nomination contests.

Looking ahead to the general election, war-weary voters seem ready for change.

A mid-April Gallup poll showed people preferring the Democratic Party over the Republican to win the presidency by a substantial 51 percent to 38 percent. Democrats had a 43 to 34 advantage in a Quinnipiac University poll one week ago.

Yet in face-offs in which Gallup and Quinnipiac pitted the top contenders against each other, the two Republicans won most matchups and came out even in the others. The strongest showing was by Giuliani, who was preferred by up to 9 points.

The Newsweek survey gave Democrats more hope, with Clinton, Obama and former Sen. John Edwards leading when matched against the top Republican contenders, except that Clinton and Giuliani ran about even.

"They show Hillary definitely can win," Mark Penn, Clinton's chief strategist, said of the discrepancy between the party matchups and the candidates' head-to-head pairings. "After she is nominated there will be a huge consolidation of votes among Democrats and she'll shoot up a number of points."

Andrew Kohut, who heads the nonpartisan Pew polls, said the ability of the Republican front-runners to outperform their party in the surveys should give Democrats pause.

"Presidential elections basically come down to continuity versus change, and there's certainly a predisposition to change," he said.

Guiliani and McCain are both viewed as "quite different from Bush" and could have legitimate chances of winning in 2008, presuming the conservatives who dominate the Republican select either of them as the candidate, Kohut said.

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