Barack Obama Tuesday swept a trio of Washington D.C-area nominating contests, carving into White House rival Hillary Clinton's powerbase of white and women voters and sending shockwaves through her faltering campaign.

The surging Democrat coasted to emphatic victories in Virginia, Maryland and Washington D.C, to take his win streak over the last week to eight and extend his lead in convention delegates.

Another grim night left Clinton badly needing wins in Texas and Ohio on March 4 to keep her hopes of becoming the first woman president alive.

Presumptive Republican nominee John McCain meanwhile landed his own triple blow of primaries, but faced a tougher-than-expected battle from rival Mike Huckabee in Virginia, reflecting his struggle to win over conservative voters.

Obama celebrated his wins at a rally in midwestern Wisconsin, which votes on February 19, and where he hopes to drive another dagger into Clinton's campaign.

"We won the state of Maryland. We won the Commonwealth of Virginia. And though we won in Washington, D.C., this movement won't stop until there's change in Washington, D.C."

Obama barely referred to Clinton at all, and instead turned his fire on McCain, in a preview of a potential November general election matchup.

With 90 percent of precincts reporting in Virginia, Obama led Clinton, who ousted her campaign manager amid a growing sense of crisis at the weekend, by a dominating 63 percent to 36 percent.

With 85 percent of Republican precincts reporting in the same state, McCain led Huckabee by 49 to 42 percent.

Obama's growing head of steam held ominous signs for the Clinton campaign, in a trio of contests that offered 168 of the 2,025 Democratic delegates needed to win the nomination, to be doled out in a proportional system.

In a rolling count of nominating delegates by RealClearPolitics.com, Obama led with 1,207 to 1,194, including Virginia's tally. A total of 2,025 delegates is needed for the nomination.

The role of some 440 still-undecided super-delegates -- party luminaries who can choose to vote for either candidate -- is now likely to be critical.

A defiant Clinton showed no sign of giving up the fight, but now faces must-win contests in Ohio and Texas on March 4.

"We're going to sweep across Texas in the next three weeks, bringing our message about what we need in America, the kind of president that will be required on Day One to be commander in chief to turn the economy around," she said after flying into Texas even before Washington DC area voting had closed.

"I'm tested. I'm ready. Let's make it happen!" she told a rowdy rally in El-Paso, Texas in a veiled reference to Obama's perceived inexperience.

Exit polls in Virginia showed Obama overhauling the former first lady's normal bastion of women 58 percent to 42 percent, and splitting another of her key powerbases, white voters.

He won 90 percent of black voters and extended his hold of younger voters, many of whom are being turned on to politics for the first time by his soaring rhetoric and message of hope.

Virginia had been seen as Clinton's best shot of halting Obama's hot hand, after he swept five weekend contests, and she will now look to delegate-rich contests in Ohio and Texas on March 4 to reignite her hopes.

Among those voters in Virginia who put a priority on the economy, Clinton's bread and butter issue, Obama still came out on top 60 to 40 percent.

Virginia was the biggest prize with 83 Democratic delegates up for grabs. Maryland had 70 on offer, and the US capital, a special federal district, 15.

In one symbolic boost, Clinton snapped up the endorsement of former Ohio senator and astronaut John Glenn.

"She has the strength and experience to take on the Republicans in November and win Ohio and the White House," Glenn said.

PHOTO CAPTION

Democratic presidential hopeful Sen. Barack Obama, D-Ill., speaks at a rally Tuesday, Feb. 12, 2008, in Madison. (AP)

Reuters