WASHINGTON (Reuters) - Hurricane Sandy blew the U.S. presidential race off course on Sunday even before it came ashore, forcing Republican Mitt Romney to shift his campaign inland and fueling fears that the massive storm bearing down on the East Coast could disrupt an election that is already under way.

As he juggled his governing duties with his re-election effort, President Barack Obama said the heavily populated East Coast could face power failures and other disruptions for several days.

"Don't anticipate that just because the immediate storm has passed that we're not going to have some potential problems in a lot of these communities going forward through the week," Obama said after a visit to the federal government's storm-response center.

Romney rerouted his campaign from Virginia to join his vice presidential running mate Paul Ryan in Ohio, one of the handful of battleground states that will decide the outcome of the November 6 election.

"You are the battleground of battlegrounds. You get to decide," Ryan told a crowd of 1,000 people who were not able to join 2,000 others in a high school gymnasium in Celina, Ohio.

Obama later flew to Florida for a campaign stop. Like Romney, he canceled events in Virginia, a battleground state that could bear the brunt of the storm's impact. Obama canceled plans to campaign in Ohio after Monday's event in Florida, opting to return to the White House instead.

"I'm not going to be able to campaign quite as much over the next couple of days," Obama told volunteers at a local campaign office in Orlando late on Sunday. "So you guys gotta carry the ball!" he said to cheers.

Both campaigns also canceled events in New Hampshire, which could face high winds and heavy rain.

"The last thing the president and I want to do is get in the way of anything. The most important thing is people's safety and people's health," Vice President Joe Biden told campaign volunteers in Manchester, New Hampshire, before leaving for Ohio.

Officials in the path of the storm scrambled to ensure that extended power outages would not disrupt the early voting that appears to be critical for both candidates this year.

Obama said he did not think the storm would impact voting, but some on his campaign staff were not so certain.

"Obviously we want unfettered access to the polls because we believe that the more people that come out, the better we'll do," top Obama adviser David Axelrod said on CNN.

Republican Virginia Governor Bob McDonnell said his state plans to extend early voting hours and restore power quickly to election facilities in the event of outages.

Officials in neighboring Maryland said early voting stations would close on Monday.

WINDS OF UNCERTAINTY

The looming storm threw another note of uncertainty into a race that remains a statistical dead heat.

The vast majority of voters have made up their minds at this point, and more than one in five have already cast their ballots. But the storm could throw a wrench in the campaigns' efforts to drive voters to the polls in the final days before the election and will require them to ensure that their armies of door-knocking volunteers stay safe.

An extended power outage could sideline millions of dollars worth of television advertising that is set to saturate the airwaves in the final days of the race.

It also scrambles their efforts to schedule rallies in the handful of states that are likely to decide the outcome.

"The poll numbers aren't changing that much and I don't think the storm is going to change that dynamic. It's just going to present logistical challenges for the campaign," Hunter College political science professor Jamie Chandler said.

A severe disruption could hurt Obama more than Romney because his campaign has counted on early voting to lock up the support of those who may be less likely to vote on Election Day, Chandler said.

Officials from both campaigns said they were confident they would be able to get their message out and drive voters to the polls over the coming days. But they recognized that, after years of obsessive planning and nearly $2 billion in campaign expenditures, the storm had introduced a last-minute element of chaos.

"There's certain things we can't control and nature is one of them. We try to focus on the things that we can control," Romney adviser Kevin Madden told reporters.

There is some evidence that natural disasters can hurt an incumbent's re-election chances as voters often blame whoever is in office for adversity.

Research by Larry Bartels of Vanderbilt University and Christopher Achen of Princeton University found that Vice President Al Gore may have lost the election in 2000 because of severe drought and excessive rainfall in seven states.

Bush's approval ratings plummeted after Hurricane Katrina devastated New Orleans in 2005, and voters could similarly blame Obama if the government fumbles its response to this storm.

But there are also dangers for Romney, who will have to be careful to avoid being seen as politicizing the disaster. His campaign's hasty response to the attacks on U.S. diplomatic missions in the Middle East in September was widely criticized.

The Obama campaign said it would suspend fundraising e-mails in the mid-Atlantic region on Monday and encouraged supporters to donate to the Red Cross.

Opinion polls show the race to be essentially tied at the national level.

A Reuters/Ipsos tracking poll released on Sunday found Obama leading Romney among likely voters by 49 percent to 46 percent, within the online survey's credibility interval. Among all registered voters, Obama held a wider lead of 51 percent to 39 percent.

However, Obama retains a slim advantage in many of the battleground states that will decide the election.

A Washington Post poll released on Sunday found Obama leading Romney by 51 percent to 47 percent in Virginia, just outside the poll's margin of error.

In Ohio, a poll by a group of newspapers found the two tied at 49 percent each. Other polls have shown Obama ahead there.

Romney received the endorsement of Iowa's largest newspaper, the Des Moines Register, which has not backed a Republican since 1972. He also won the endorsement of newspapers in Richmond and Cincinnati.

Obama won the endorsement of newspapers in Miami, Detroit and Toledo, Ohio, as well as The New York Times.