COLUMBUS, Ohio, March 5, 2008 (AFP) - Democrat Hillary Clinton racked up stunning primary victories Tuesday over Barack Obama in Ohio and Texas, resurrecting her flagging White House hopes and setting the stage for an epic nominating end-game.

Clinton's comeback prolonged the longest and costliest nominating race in US history and ensured weeks or months more of bruising battle for the right to face John McCain, who clinched the Republican mantle Tuesday.

The feisty senator and former first lady, her campaign threatened with oblivion, took Ohio, Texas and Rhode Island, ending Obama's 12-contest win streak after he started the evening with a victory in Vermont.

But Obama, a freshman senator from Illinois, stressed she still faced tough odds to overhaul his lead of about 100 in the race for the 2,025 delegates needed to win the Democratic nomination.

"No matter what happens tonight, we have nearly the same delegate lead as we did this morning, and we are on our way to winning this nomination," Obama, 46, told an outdoors rally in balmy San Antonio, Texas. Obama, seeking to become the first black US president, and Clinton, vying to be the country's first woman chief executive, turned their sights on their next big showdown in Pennsylvania on April 22.

But some analysts predicted the fight could go all the way to the Democratic convention in August with the outcome decided by so-called "superdelegates" - party luminaries who can vote as they like.

With nearly all precincts reporting in Ohio, Clinton had a 55-43 percent edge over Obama. She led 51-47 percent in Texas, which followed its primary vote with caucuses in a two-step delegate selection process.

Clinton came up big after launching an all-out attack on Obama's ability to protect the United States, including a controversial ad aired three days ago featuring children sleeping as a crisis broke over the White House.

Obama accused Clinton of fear-mongering but some analysts suggested the tactic worked. Texas exit polls showed more than 60 percent of people who made up their minds in the last three days opted for Clinton.

"I think what's noteworthy is a lot of pundits thought we were coming tonight to a funeral for Hillary Clinton," said Paul Begala, a former aide to president Bill Clinton. "Instead we saw a resurrection."

Clinton signaled she would press the attack in the weeks ahead in what could be an increasingly nasty campaign.

"We have two wars abroad, we have a recession looming here at home," she told the Ohio rally. "Voters faced a critical question. Who is tested and ready to be commander in chief on day one? And who knows how to turn our economy around, because we sure do need it."

McCain, 71, also capped an amazing comeback after his campaign had looked dead and buried in mid-2007, crippled by overspending and infighting that led to an exodus of top aides.

But now, McCain can enjoy laying out his lines of attack for the November election while watching the Democrats fight tooth and nail.

The Arizona senator promised to combat Islamic extremism, keep the US economy open to world trade and lower taxes if elected the successor to George W. Bush, whose blessing he was to receive at the White House on Wednesday.

"And I am very pleased to note that tonight, my friends, we have won enough delegates to claim with confidence, humility and a sense of great responsibility that I will be the Republican nominee for president of the United States," he told cheering supporters in a Dallas hotel.

His victories Tuesday took McCain, a Vietnam war hero distrusted by many conservatives for his maverick stance on issues such as immigration, over the Republican finish line of 1,191 delegates.

His last remaining challenger, former Arkansas governor Mike Huckabee, bowed out and pledged fealty to the Republicans' new standard-bearer.