SCENARIOS: How Obama, McCain are faring in key states

(Reuters) - Tuesday's U.S. presidential election will be decided in about a dozen battleground states where most opinion polls show Democrat Barack Obama ahead of Republican rival John McCain.

Obama, who leads in every national opinion poll, is ahead in all the states won by Democrat John Kerry in 2004 as well as in several states won by Republican President George W. Bush, recent polls show.

A series of Reuters/Zogby polls released on Monday showed Obama ahead of McCain in six of eight battleground states, including the big prizes of Florida and Ohio.

The victor needs 270 electoral votes to win the Electoral College and capture the White House.

The president is determined not by the most votes nationally but by a majority of the Electoral College, which has 538 members allotted to all 50 states and the District of Columbia in proportion to their representation in Congress.

Each state, except Maine and Nebraska, awards its votes to the candidate who gets the most votes in the state. Maine and Nebraska split them by congressional district.

Here are some battleground states with their electoral vote totals, 2004 results and recent details about the contests in each state.

* Colorado -- Nine electoral votes. Bush beat Kerry 52 percent to 47 percent in the state in 2004, but since then, Democrats have won the state legislature and governor's office. The three latest polls put Obama up by between 5 and 7 points.

* Florida -- 27 electoral votes. Bush beat Kerry 52 percent to 47 percent in a state known for the disputed result that decided the 2000 election. Florida is a classic swing state with many older voters who could favor McCain along with Jewish voters who are normally Democratic but have been wary of Obama. The three most recent polls each gave Obama a narrow lead of just 2 points in the state, one of the biggest prizes in the election.

* Indiana -- 11 electoral votes. Bush beat Kerry by 20 points in 2004 in a state that last voted for a Democrat in 1964. But it borders Obama's home state of Illinois and he has poured resources into his Indiana campaign after finishing a strong second to Sen. Hillary Clinton in the May Democratic primary. The Reuters/Zogby poll on Monday showed McCain in the lead by 5 points, although earlier polls had showed the race as a dead heat.

* Missouri -- 11 electoral votes. Bush beat Kerry 53 percent to 46 percent in 2004 in a classic battleground with a mix of cities and conservative rural areas. The two most recent polls split, one with Obama up by 1 point and the other with McCain ahead by 1 point.

* New Hampshire -- Four electoral votes. Kerry beat Bush by 1 point in 2004. McCain's history of big primary wins in New Hampshire in 2000 and this year gives him hope he can take the state in November. Democrats captured both the state's seats in Congress and gained control of the state Legislature in 2006 in an anti-Republican wave on which Obama hopes to capitalize. A poll on Sunday showed Obama ahead by 11 points.

* New Mexico -- Five electoral votes. Bush beat Kerry by fewer than 6,000 votes in 2004. As the senator from neighboring Arizona, McCain is familiar to many New Mexico voters, but he will have to battle Obama for the growing bloc of Hispanics, who make up more than 40 percent of the state's population. The most recent poll shows Obama ahead by 10 points.

* Nevada -- Five electoral votes. Bush beat Kerry by 20,000 votes in 2004 in a state won by Republicans in eight of the past 10 presidential elections. As in New Mexico, the burgeoning Hispanic population will be crucial -- it now makes up nearly a quarter of Nevada's residents. The Reuters/Zogby poll on Monday gave Obama a lead of 8 points.

* North Carolina -- 15 electoral votes. Bush beat Kerry by 12 points in 2004, even though the Democratic vice presidential nominee, John Edwards, was from the state. More than one-fifth of the population is black and an influx of transplants to high-tech urban areas have given Obama a chance. One recent poll gave McCain a 3-point edge, one gave him a 1-point advantage and one showed Obama 1 point ahead.

* Ohio -- 20 electoral votes. Bush beat Kerry by about 120,000 votes in the state that ultimately decided the 2004 race. No Republican has won the White House without Ohio, and McCain will have a hard time piecing together a win without the state. One new poll on Monday showed Obama ahead by 7 points, two others gave him a 6-point edge and one a 2-point lead. Another poll on Sunday had McCain up by 2 points.