WASHINGTON (Reuters) - Democrat Barack Obama easily beat rival Hillary Clinton in Mississippi on Tuesday, giving him new momentum in their heated presidential fight as they head to the next showdown in Pennsylvania in six weeks.

Obama, who would be the first black U.S. president, rode a wave of heavy black support to victory and extended his lead over Clinton in pledged delegates to the August nominating convention. The Illinois senator also won on Saturday in Wyoming.

Clinton revived her hopes in the Democratic race last week by beating Obama in primaries in Ohio and Texas, prolonging their bitter Democratic fight for the right to face Republican John McCain in November's presidential election.

"What we have tried to do is steadily make sure that in each state we are making the case about the need for change in this country, and obviously the people of Mississippi responded," Obama said in an interview on CNN.

Clinton did not speak publicly after the result, but her campaign manager, Maggie Williams, released a statement thanking the New York senator's supporters in Mississippi.

"Now we look forward to campaigning in Pennsylvania and around the country as this campaign continues," Williams said.

Both candidates were already in Pennsylvania on Tuesday, looking ahead to its April 22 contest that has 158 delegates at stake -- the biggest single-state haul remaining in the race for the nomination.

While voters in Mississippi were still casting their ballots, racial remarks about Obama by a prominent Clinton supporter sparked a harsh exchange between the two camps.

"If Obama was a white man, he would not be in this position," Geraldine Ferraro, the Democratic vice presidential candidate in 1984 and the only woman ever nominated by a major party for either of the top two U.S. political offices, told a California newspaper.

"And if he was a woman he would not be in this position. He happens to be very lucky to be who he is. And the country is caught up in the concept," Ferraro said.

Clinton said she did not agree with the comments and called them "regrettable," but the Obama camp accused her of a double standard for refusing to rebuke Ferraro and remove her from her finance position with the campaign.

Obama's top foreign policy adviser resigned last week after telling a British newspaper Clinton was "a monster."

"I don't think Geraldine Ferraro's comments have any place in our politics or in the Democratic Party. They are divisive," Obama told a Pennsylvania newspaper.

"I would expect that the same way those comments don't have a place in my campaign they shouldn't have a place in Senator Clinton's either," he said.

VOTER BLOCS

Exit polls in Mississippi showed Obama won about 90 percent of black voters, who were expected to make up about half of the state's Democratic primary electorate, and continued to hold big leads among young voters.

Clinton, a New York senator and former first lady, retained her advantage with older voters, exit polls showed. The two candidates have developed consistent bases of support within the Democratic Party.

Obama's win in Mississippi will add to his nearly insurmountable lead over Clinton in the pledged delegates who will help decide the nominee. Mississippi has 33 pledged delegates at stake.

But neither Obama nor Clinton is likely to reach the 2,025 delegates needed to clinch the nomination without help from nearly 800 "superdelegates" -- party officials and insiders free to back any candidate.[MORE]