President Bush continues to lead rival Sen. John F. Kerry among likely voters despite surging enthusiasm for Kerry among Democrats and new doubts about whether the president has a clear plan to deal with terrorism and the situation in Iraq, according to the Washington Post tracking poll.

In the aftermath of last week's presidential debate, Bush currently leads Kerry 51 percent to 46 percent among those most likely to vote, according to polling conducted Friday through Sunday. Independent candidate Ralph Nader claims 1 percent of the hypothetical vote.

But the president held only a 3-point advantage among all registered voters, down from 7 points in a Post-ABC News survey conducted before last week's presidential debate. Kerry is particularly popular among occasional voters -- a sign that the election may hinge for Kerry on his campaign's ability to get newly registered voters and those with only a spotty voting record to go to the polls.

In order to provide a daily snapshot of the campaign, the Post began Friday to conduct nightly election surveys. Each day now through the election, the results of the previous three days of interviewing will be averaged together and reported on washingtonpost.com.

A total of 1,470 registered voters were interviewed for the first wave of the tracking survey, including 1,169 who were determined to be likely voters based on voting intention, interest in the campaign and past voting history. Margin of sampling error for results based on either sample is about plus or minus 3 percentage points.

By a ratio of more than 2-1, these likely voters interviewed over the weekend said Kerry won the first debate on foreign policy and terrorism. As a result, the Democrat revived his flagging campaign and sparked a new wave of enthusiasm among his supporters.

The proportion of likely voters with a favorable view of Kerry grew from 39 percent immediately before the date to 47 percent in the latest poll. At the same time, the proportion of voters with an unfavorable of him dropped by 3 points to 42 percent. However, Bush still remains slightly more popular, with 53 percent of all likely voters saying they had a favorable impression of him.

Kerry's strong debate performance also energized his supporters while Bush's lackluster showing seems to have damped the spirits of his partisans.

Half of Kerry's voters now say they are "very enthusiastic" about their candidate, up eight points since before the debate. At the same time, the share of Bush voters who were similarly excited about their candidate dropped by eight points to 57 percent, narrowing the enthusiasm gap from 23 to 7 points in a few short days. Democrats, men, 40 to 49-year-olds and better educated Kerry supporters led the increase in the intensity of enthusiasm for him, the survey found.

Bush is still seen as the one with the clearest plan for dealing with Iraq and terrorism, although Kerry clearly made inroads on both issues during his first debate.

According to the survey, barely half -- 51 percent -- of all voters said Bush has a "clear plan" for handling the situation in Iraq, down from 55 percent before the debate. The proportion who doubted that Bush has a plan grew by 6 points to 48 percent.

At the same time, 42 percent said Kerry has a plan for Iraq -- a 5-point increase -- while the proportion who said he does not fell by four points to 52 percent.

Similarly, those who believed Bush had a clear plan for handling terrorism declined while Kerry improved, though the president still has a commanding 18-point advantage over Kerry on this issue.

Despite this movement, the latest Post poll found that other key measures of the two candidates were unchanged by the debate. Bush is still viewed by likely voters as the one best able to deal with Iraq and the terrorist threat. And more than half -- 52 percent -- said Bush is better qualified to be commander-in-chief while 43 percent said Kerry was, virtually unchanged from the pre-debate survey.

In addition, the president retained his advantage over Kerry as the candidate who would make the country safer and more secure and be the stronger leader.

Other surveys also released Monday showed large variation, suggesting great volatility in the electorate following last Thursday's debate. A poll by Gallup found support for Kerry had increased significantly since the debate and the race was now deadlocked. A Zogby poll had Bush ahead by a single percentage point, largely unchanged from a pre-debate poll. But a Pew Center for the People & the Press poll found Bush with a 5-point advantage, essentially the same as its survey released before Thursday's debate.