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Presumptive Democratic presidential candidate Sen. Barrack Obama (D-IL) speaks at the 25th annual conference of National Association of Latino Elected and Appointed Officials (NALEO) in Washington on June 28, 2008. (UPI Photo/Alexis C. Glenn)

The Gallup Poll Daily tracking shows Obama leading McCain, 48 percent to 42 percent.

The three-day rolling average is based on interviews conducted in the two days before the July Fourth holiday, July 2-3, and Saturday, July 5.

About 5 percent of respondents said they will not vote for either major party candidate, while a 6 percent say they are undecided.

"Until the vice presidential nominees are announced and/or the Democratic convention begins in late August, the twin efforts of the campaigns to influence voter perceptions of the race and of the news media to find something new and compelling to say about the race will be competing for what could be sparse voter attention," Gallup said in its analysis.

The sample of 2,620 registered voters has a margin of sampling error of plus or minus 2 percent.