WASHINGTON (Reuters) - Democrat Barack Obama leads Republican John McCain in five of eight key battleground states as Americans prepare to vote in the White House race, according to a series of Reuters/Zogby polls released on Tuesday.

Obama expanded his national lead to 11 points over McCain among likely U.S. voters in a separate Reuters/C-SPAN/Zogby tracking poll, up from 7 points on Sunday. The telephone poll has a margin of error of 2.9 percentage points.

Obama appeared to be firmly in command of the presidential battle as Americans head to the polls on Tuesday, with McCain struggling to beat back a challenge from Obama in about a dozen states won by President George W. Bush in 2004.

The new state surveys showed Obama with a slim 1-point lead in Florida and 2-point edge in Ohio, within the margin of error of 4.1 percentage points. Obama had bigger leads in Virginia and Nevada.

Those four states, all won by Bush in the last election, have a combined 65 electoral votes. Along with states won by Democrat John Kerry in 2004 where Obama safely leads, they would give Obama 317 electoral votes -- more than the 270 needed to win the White House.

Obama leads by 10 percentage points in Pennsylvania, which McCain has targeted as his best chance to steal a state won by Kerry in 2004.

The classic bellwether state of Missouri, where Obama led by 1 percentage point on Monday, is now dead even at 49 percent.

McCain leads Obama by 5 points, 50 percent to 45 percent, in Indiana, a state that has not supported a Democrat for president since 1964. Obama plans an Election Day visit there to try to drum up the vote.

McCain leads Obama by a 1-point margin in North Carolina, which has not been in the Democratic column since 1976.

“Obama’s national lead grew overnight as the undecideds decided he defines the mantle of change,” said pollster John Zogby. “It looks like it could be a big victory for Obama, and McCain has to win essentially all of the states still in play.”

TWO BIG PRIZES

The race was tight in the states that offer the two biggest prizes where the outcome is uncertain -- Florida with 27 electoral votes and Ohio with 20. An Obama victory in either could kill McCain’s hopes of a comeback win.

In Florida, Obama leads McCain 49 percent to 48 percent. The two were dead even at 47 percent one week ago. Obama’s Ohio lead is 49 percent to 47 percent, down from a 6-point edge on Monday.

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Obama widened his edge in Nevada from 8 points to 11 points and now leads 53 percent to 42 percent. He also expanded his advantage in Virginia, where he concluded his campaign on Monday with a late-night rally, from 6 to 9 points and now leads 52 percent to 43 percent.

In the national poll, Obama moved to big leads among some of the crucial voting blocs on Tuesday. Obama leads by 24 points among independents and 19 points among women. He leads in every age group and among every income level.

McCain’s lead among whites fell from 13 points to 7 points, and he is attracting just 29 percent of Hispanics. In 2004, Bush won more than 40 percent of Hispanics.

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Both independent Ralph Nader and Libertarian Bob Barr were at 1 percent in the survey.

The rolling national tracking poll, taken Friday through Sunday, surveyed 1,226 likely voters in the presidential election. In a tracking poll, the most recent day’s results are added, while the oldest day’s results are dropped to monitor changing momentum.

The state surveys were taken Friday through Monday with a sample in each state of between 600 and 605 likely voters. The margin of error in all eight states was 4.1 percentage points.