Washington (AP): Barack Obama stands alone at last among Democrats seeking the White House, strongly endorsed by former rival Hillary Rodham Clinton but still facing the ponderous challenge of wooing her base for the fight against Republican John McCain.

Clinton finally suspended her campaign _ but did not fully abandon it _ with a 28-minute speech and 14 mentions of her rival, telling supporters:

``I endorse him and throw my full support behind him.''

But the polls show Obama faces a stiff task in winning over Clinton's deeply disappointed female supporters, not to mention her base among working-class whites as a whole.

In a spirit of reconciliation and of political necessity, however, Obama began working in that direction in a statement after watching Clinton's Saturday speech on the Internet.

``I honor her today for the valiant and historic campaign she has run,'' he said, while taking a rare weekend break with his family at his Chicago home. ``She shattered barriers on behalf of my daughters and women everywhere, who now know that there are no limits to their dreams.''

On Monday, Obama will travel to North Carolina _ a state that has not voted for a Democratic presidential candidate since 1976 _ to launch a two-week national tour in key battleground states in which he intends to highlight his differences on economic issues with McCain, the veteran Arizona senator. It comes at a time when Americans are growing increasingly uneasy over the faltering U.S. economy, reflected in rising home foreclosure and unemployment rates and record-high oil prices.

With some supporters in tears, Clinton called for Democratic unity as the party stands to stride past cultural and political milestones that she and Obama, the first black to secure a major party presidential nomination, represent.

``Children today will grow up taking for granted that an African-American or a woman can, yes, become the president of the United States,'' she said.

More than 17 months after she announced her run to become America's first woman president _ a campaign that seemed unstoppable at the start _ Clinton had accumulated about 18 million votes in the Democratic primaries.

``Although we weren't able to shatter that highest, hardest glass ceiling this time, thanks to you, it has about 18 million cracks in it and the light is shining through like never before,'' she said before a crowd of supporters jammed into the ornate National Building Museum, not far from the White House she longed to occupy again.

In one of her most relaxed performances since the campaign began, Clinton repeatedly reminded listeners of the new threshold her candidacy had set for women _ the rock solid bloc of her coalition.

The new Clinton role, however, was to heal wounds opened in the sometimes bitter battle with Obama _ especially the historic open sores of gender and race in America.