The new poll shows Illinois Sen. Obama ahead of Sen. McCain of Arizona by 50 percent to 44 percent among likely voters with 2 percent of respondents supporting Ralph Nader and 1 percent backing Libertarian candidate Bob Barr.

The poll was conducted between October 20 and 27 by Harris Interactive and surveyed 2,303 adults, 1,695 of whom were identified as likely voters.

Harris says 12 percent of those likely voters have already cast ballots preferring Obama over McCain by 9 points, 51 percent to 42 percent.

Fifteen percent of those surveyed who voted for President George W. Bush in 2004 said they were likely to vote for Obama this time around. Eleven percent who reported voting for Sen. John Kerry, D-Mass., in the last election indicated they were likely to cast a ballot for McCain this year.