The CNN/Opinion Research Corp. survey does show Obama, the senator from Illinois, with a 5-point advantage over McCain, the senator from Arizona, 50 percent to 45 percent. However, with the statistical margin of error, the race appears to be virtually a dead heat.

Last month, Obama held a 46 to 43 percent edge over McCain, the pollsters said. Other recent national polls have produced similar results.

The CNN/ORC poll indicates Obama's edge gets thinner when independent candidate Ralph Nader and Libertarian candidate Bob Barr are inserted in the mix. In that situation, Obama's lead over McCain slips to 46 percent to 43 percent, with Nader garnering 6 percent and Barr a 3 percent slice.

The poll, conducted June 26-29, surveyed 906 registered voters and carries a margin of error of plus or minus 3.5 percentage points.