The survey by Public Policy Polling (PPP), which includes several Democrats as clients, shows both presidential candidates with 45 percent. Ten percent remain undecided, according to the poll.

PPP noted that Obama (D-Ill.) led the Arizona Republican in Ohio polls it conducted in June and July. It suggested that Obama’s support among Democrats is softer than McCain’s support among Republicans.

While McCain gets the backing of nearly nine in 10 Republican voters, Obama gets the support of only three-quarters of Democrats. Obama leads among independents.

Obama's results with Democratic voters could be linked to lingering resistance among supporters of his former rival for the Democratic nomination, Sen. Hillary Rodham Clinton (N.Y.).

Many of the Democrats who aren't supporting Obama “are disproportionately white, female, and middle-aged, an indication that it could be former supporters of Hillary Clinton who are holding out,” according to the pollster's analysis.

"Ohio is one state, along with Pennsylvania and Michigan, where Barack Obama would probably be well-served by some joint appearances with the Clintons," wrote Dean Debnam, PPP's president. "Democrats have a party ID advantage in Ohio, but that won’t do much for them unless the voters in their party actually vote for their nominee."

In March, Clinton defeated Obama in the Ohio Democratic Primary by 10 points.