WASHINGTON — Minority Americans have been flocking to the nation's "swing counties," hotly contested areas that could play a crucial role in this year's election.

Blacks and Hispanics are moving to counties that already were racially diverse, such as Osceola in central Florida and Mecklenberg in North Carolina, home to Charlotte. They also are moving to key counties that remain predominantly white, such as Lake in northeast Ohio, Lehigh in eastern Pennsylvania and Oakland outside Detroit.

Given the closeness of the past two presidential elections, even small changes could make a difference in competitive states.

The changes reflect national trends: 93 percent of all counties are less white than at the start of the decade, according to new Census estimates. The changes are even more profound in swing counties of potential battleground states, counties that were decided by razor-thin margins in 2000 and 2004 and could decide statewide winners this year.

"The key this time is there are a fair number of battleground states that are becoming more diverse, and maybe diverse enough to make a difference," said William Frey, a demographer at the Brookings Institution, a Washington think tank.

The Census Bureau last week released 2007 data on race, age and Hispanic origin for all 3,141 counties in the nation. The Associated Press used that to analyze 129 key counties in 14 states expected to be the most competitive in this year's presidential election. Each county was decided by no more than 5 percentage points in the past two elections, and each sits in a state that could go either way this year.

The analysis found that from 2000 to 2007, minorities made up a growing share of the population in all but 12 of the swing counties. The changes happened among every age group, even seniors, though they were much more pronounced among the young, including those too young to vote.

Barack Obama overwhelmingly won the black vote in the Democratic primaries, and is polling more strongly than Republican John McCain among Hispanics. Obama also has a big lead among voters younger than 34, according to a recent AP-Ipsos poll.

The Census numbers are estimates, but the nation is becoming increasingly diverse and even more so in areas that have been decisive in the past two presidential elections.

The AP analysis looked at counties in Colorado, Florida, Georgia, Indiana, Iowa, Michigan, Missouri, North Carolina, New Hampshire, New Mexico, Ohio, Pennsylvania, Virginia and Wisconsin. Nevada also was analyzed because it is a competitive state this year.

The nation's minority population has grown through higher birthrates and immigration. As a result, the share of minorities increased between 2000 and 2007 in every state but Hawai'i and the District of Columbia.

In the 129 swing counties analyzed, the black population grew by an average of 18 percent, Hispanics by 45 percent, and the white population by less than a percent.