SCENARIOS-How candidates are faring in key U.S. states

(Reuters) - The U.S. presidential election on November 4 hinges on a handful of battleground states where opinion polls show Democrat Barack Obama making significant gains against his Republican rival John McCain.

Obama leads in all of 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.

Even Florida and Ohio, pivotal states that swung the 2000 and 2004 elections to the Republicans, also appear to be leaning towards the Democratic candidate, according to poll results.

Obama or McCain need 270 electoral votes to win the Electoral College and capture the White House.

The president is determined not by the most votes nationally but 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. Two polls this week show Obama ahead by 6 points, holding a lead that opened as the financial crisis moved to centre stage in the campaign.

* 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 a heavy concentration of older voters who could favour McCain. It also has many Jewish voters who are normally Democratic but have been wary of Obama. A poll on Friday gave Obama an 8-point edge, while earlier surveys have shown him with a narrower lead in a state McCain must win.