WASHINGTON -- Add this to the divisive debate over race in the presidential campaign: Whites who said race was important in picking their candidate have been about twice as likely to back Sen. Hillary Rodham Clinton as Sen. Barack Obama.

Exit polls of voters in Democratic primaries also show that whites who considered the contender's race -- Clinton is white, Obama is black -- were three times likelier to say they would only be satisfied with Clinton as the nominee than if Obama were chosen.

The figures shed some light on race's effect on a competition that moves to the April 22 primary in Pennsylvania, which has a slightly greater proportion of whites than average. The numbers also underscore the challenge Obama could face in the general election, when whites will comprise a larger share of voters and tend to be more conservative than those participating in the Democratic primaries.

Whites who said race influenced their decision were outnumbered more than six to one by those saying it was insignificant. Whites who say they discounted race also leaned toward Clinton, though by more modest margins.

In the exit polls, whites saying they considered the candidate's race were likelier to be from the South and rural areas, less educated, lower earning and older. That's consistent with voting so far, in which Obama has done better among whites with more education and higher incomes, especially men.