WRAPUP 12-Democrat Obama rolls to three big U.S. wins

(Updates with Obama, McCain speeches)

By John Whitesides, Political Correspondent

WASHINGTON, Feb 12 (Reuters) - Barack Obama easily won three more Democratic nominating contests on Tuesday, extending his winning streak over rival Hillary Clinton and building momentum in a hard-fought U.S. presidential race.

Obama rolled to decisive victories in Virginia, Maryland and the District of Columbia, running his hot streak to eight consecutive wins and expanding his lead in pledged convention delegates who select the party's nominee.

"Tonight, we're on our way. But we know how much further we have to go," Obama told supporters in Madison, Wisconsin, where the next showdown occurs in a week. "We know our road will not be easy. But we also know that at this moment the cynics can no longer say our hope is false."

Republican front-runner John McCain also swept to wins over his last major challenger, former Arkansas Gov. Mike Huckabee, in the U.S. capital area contests as he moved closer to clinching the party's nomination for the November election.

McCain already was looking forward to a general election match-up with the Democrats after Tuesday's wins, which will increase pressure on Huckabee to give up his White House quest.

"Now my friends comes the hard part, and for America, the much bigger decision," McCain, an Arizona senator, told supporters in Alexandria, Virginia.

"We do not know for certain who will have the honor of being the Democratic Party's nominee for president. But we know where either of their candidates will lead this country, and we dare not let them," he said.

The wins for Obama, who would be the first black U.S. president, followed big weekend triumphs in Maine, Louisiana, Nebraska, Washington and the Virgin Islands.

All three of Tuesday's contests occurred in fertile territory for Obama, with large populations of the highly educated, high-income and black voters who have favored the Illinois senator.

But exit polls indicated Obama dramatically expanded his support and cut into Clinton's core groups. Obama led among women, Hispanics and lower-income voters in Virginia and essentially split the votes of whites with Clinton. In Maryland, he captured seniors and rural voters.

"This is the new American majority," Obama said. "This is what change looks like when it happens from the bottom up."

Obama already had edged past Clinton in the race for pledged delegates who formally select a party nominee at a convention in August. A total of 168 Democratic delegates were at stake in Tuesday's voting.

Obama had 1,017 pledged delegates to Clinton's 942, according to a count by MSNBC -- well short of the 2,025 needed to clinch the Democratic nomination.

DAUNTING LEAD FOR MCCAIN