WASHINGTON (Reuters) - President Barack Obama and Republican Mitt Romney remain effectively tied as public opinion remains remarkably stable less than a week from Election Day, according to a Reuters/Ipsos daily tracking poll released on Wednesday.

Obama leads Romney among likely voters by a statistically insignificant margin of 47 percent to 46 percent, the online survey found. The numbers are unchanged from Tuesday and neither candidate has held a clear lead since early October.

Other polls have suspended activity in the wake of the storm Sandy, which left millions without power along the East Coast, but Ipsos pollster Julia Clark said she saw little evidence that the disaster had affected the four-day survey's results.

"Our numbers haven't gone strange on us," Clark said. "We're still getting interviews from those areas."

Some 24 percent of those surveyed said they had already cast their ballots, providing further evidence that early voting will play a larger role than ever in the November 6 election. Among those who have not yet voted, a quarter said they planned to cast their ballots before Election Day.

Obama led Romney by 53 percent to 41 percent among the 1,660 respondents who said they had already voted.

Though the race remains tight, 52 percent expect Obama will win. Only 30 percent said they thought Romney would win, reflecting the view of experts who say Obama holds an advantage in the state-by-state battle that will determine control of the White House.

The accuracy of Reuters/Ipsos polling is calculated using a credibility interval. In this survey, the credibility interval is 3.4 percentage points for likely voters and 3.0 percentage points for all registered voters.