WASHINGTON (Reuters) - The U.S. presidential race between Barack Obama and Mitt Romney is very close in four of the critical battleground states expected to decide next week's election, but Obama has built a small lead in Virginia, according to a Reuters/Ipsos poll released on Thursday.
The incumbent Democratic president leads his Republican challenger by five percentage points among likely voters in Virginia, at 49 percent to 44 percent.
That margin exceeds the survey's 4-point credibility interval, the tool used to account for statistical variation in Internet polls.
Obama has two-point leads among likely voters in both Ohio and Florida, leaving those races statistically tied.
Romney leads by one point in Colorado, edging Obama by 47-46 percent, effectively another dead heat.
With the national race tied or nearly so in most polls, the presidency will be decided in a handful of hotly contested swing states where the battle for the White House is now mostly considered too close to call.
The trends are important despite the small size of the leads, Ipsos pollster Julia Clark said, especially in Virginia, where Obama led by just two points in poll results released on Wednesday.
"It will be one to watch very closely in the next few days," she said.
Clark said the result was not affected by superstorm Sandy, which hit parts of Virginia early this week but did not cause devastation anywhere near the impact in hard-hit New Jersey and New York.
NATIONAL RACE SEEMS STABLE
Obama led Romney by one percentage point nationally in the Reuters/Ipsos daily tracking poll conducted from October 28 to November 1, a margin within the online survey's credibility interval.
The national race has been stable as the November 6 Election Day approaches, despite a barrage of late campaign ads and the effects of Sandy. Obama has remained at 47 percent and Romney at 46 percent in the online poll for three days running.
Backing for both candidates seems solid. In the national survey, only 11 percent of Romney's supporters said they might change their mind, and just 8 percent of Obama's backers indicated the same.
About a quarter - 26 percent - of registered voters said they have already cast their ballots. Among them, Obama leads by 52 percent to 43 percent. The number is not necessarily predictive because Democrats are typically more likely to vote early than Republicans.
The state polls showed Democratic Senate candidates in Ohio and Florida leading by wider margins than Obama's advantage in the presidential race.
In Ohio, Senator Sherrod Brown led Republican Josh Mandel by 50 percent to 42 percent.
In Florida, Senator Bill Nelson led Republican Connie Mack by 52 percent to 41 percent.
Democratic candidate Tim Kaine was ahead in the Virginia Senate race, but his 47-44 percent advantage over Republican George Allen was within the survey's credibility interval.
In the national survey, the poll has a credibility interval of plus or minus 3 percentage points for registered voters and 3.4 for likely voters.
(The Reuters/Ipsos database is now public and searchable here: tinyurl.com/reuterspoll)