President Bush continues to lead 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 a Washington Post tracking poll.

In the aftermath of last week's debate, Bush 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 Bush held only a three-point advantage among all registered voters, down from seven points in a Post-ABC News survey conducted before the debate.

A total of 1,470 registered voters were interviewed, including 1,169 who were determined to be likely voters. The margin of sampling error for results based on either sample is plus or minus three percentage points.

By a ratio of more than 2 to 1, these likely voters said Kerry won the first debate, on foreign policy and terrorism. The proportion of likely voters with a favorable view of Kerry grew from 39 percent immediately before the debate to 47 percent in the new poll. Bush remains slightly more popular, with 53 percent of all likely voters saying they had a favorable impression of him.

Half of Kerry's voters say they are "very enthusiastic" about their candidate, up eight points since before the debate. The share of Bush voters who were similarly excited about their candidate dropped by eight points, to 57 percent.

Kerry made inroads on dealing with Iraq and terrorism during the first debate. According to the survey, 51 percent of all voters said Bush has a "clear plan" for Iraq, down from 55 percent before the debate; 42 percent said Kerry has a plan for Iraq -- a five-point increase. Similarly, those who believed Bush had a clear plan for handling terrorism declined while Kerry improved, though Bush still has a commanding 18-point advantage on this issue.

Other surveys released yesterday showed large variation, suggesting great volatility in the electorate. Polls by the Gallup Organization and CBS News-New York Times found that support for Kerry had increased significantly since the debate and the race was deadlocked. A Zogby International poll had Bush ahead by a single percentage point, largely unchanged from a pre-debate poll. But a poll by the Pew Research Center for the People and the Press poll found Bush with a five-point advantage, essentially the same as its survey before Thursday's debate.