Forty-seven percent of the respondents favored Obama and 45 percent were for Romney.
The Gallup-USA Today Swing States poll was conducted as part of Gallup Daily tracking in Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin.
Obama has a 4-percentage point advantage over Romney among solid supporters. Thirty-six percent of swing-state voters say they are certain they will vote for Obama in November, while 32 percent say are certain they will vote for Romney.
The remaining 11 percent who favor Obama and the 13 percent who say they lean toward Romney said there's a chance they could change their mind before Election Day, the Princeton, N.J., polling agency said.
A Politico-George Washington University Battleground Poll indicated Obama and Romney are in a virtual dead heat six months before the election. Romney's 48 percent-to-47 percent lead over Obama among likely voters is within the poll's margin of error of 3.1 percentage points.
Results for voters in 2012 election swing states are based on telephone interviews conducted April 26-May 2, 2012, on the Gallup Daily tracking survey, with a random sample of 951 registered voters living in the swing states. The margin of error is 4 percentage points.