WASHINGTON (AFP) - With the Democratic presidential nomination tantalizingly within his grasp, Barack Obama has begun to burnish his image as his party's standard-bearer in the quest to wrest the White House back from the Republicans.

Fresh from a big win over Hillary Clinton in Tuesday's North Carolina primary, and after nearly tying in Indiana, the Illinois senator was the center of attention as he made a triumphant return to Congress on Thursday.

He has also begun to train his sights on the November 4 general election, exchanging fire with likely Republican nominee John McCain while appearing on the cover of leading magazines and giving national media interviews.

Obama hopes he can finally wrap up the longest and most expensive nomination contest in US history on May 20, when primaries in Kentucky and Oregon may give him a majority of elected delegates.

His campaign is now moving faster toward a transition to the general election campaign as Obama plans stops in the coming weeks in states considered battlegrounds in the November vote, The Washington Post reported.

But with six nominating contests to go until June 3, Clinton has refused to throw in the towel and the feisty former first lady is pressing on with her campaign, focusing on the next primary fight on Tuesday in West Virginia, where she is favored to win.

"If I were part of his team, I would want to certainly foster the impression or the image that he has overwhelming momentum and that she's been defeated," said James Gimpel, government professor at University of Maryland.

"They're trying to make it look like the door's completely shut. And it's mostly shut, but I don't think that it's entirely shut," he said.

US media have all but bestowed the crown on Obama: The New York Post said Clinton was "Toast" following Tuesday's primaries, while Time magazine put Obama on its cover with the headline "And the winner is..."

But the magazine's title also had an asterisk leading to a caption saying, "Really, we're pretty sure this time."

While Obama may win the majority of elected delegates on May 20, Clinton could very well refuse to concede and press her case to the Democratic Party's "superdelegates," nearly 800 party officials who can vote for whomever they want at the August convention, that she is better placed to beat McCain.

She is also pressing the Democratic Party to reinstate the delegates from the Florida and Michigan primaries, which she won but were voided because the states violated party rules by holding their votes too early.

But Obama, who would become the first black president, has beaten back Clinton's efforts to undermine his "electability" and is progressively chipping away at her superdelegate lead, picking up at least 10 new supporters from this elite group this week.

In another sign of his growing stature, Obama was mobbed by Democratic lawmakers during an unannounced visit to Congress on Thursday, with a few unpledged superdelegates jostling to get into the camera shot with him.

"Superdelegates are not going to contravene the verdict of the pledged delegates. That would tear the party to pieces," said American University political history professor Allan Lichtman.

"There seems to be no inclination to do that. If anything Obama is picking up, not losing, superdelegates, so clearly everyone sees the handwriting on the wall," he said.

Obama leads Clinton 1,854-1,696 in total delegates, while she leads him by only seven superdelegates, 272-265, according to independent website RealClearPolitics.com. To win the nomination, a candidate needs 2,025 total delegates.

While the Democratic primaries go on, Obama has begun to focus on his battle against McCain.

At a meeting with technology workers while campaigning in Beaverton, Oregon, on Friday, Obama noticeably did not mention Clinton while assailing McCain's economic plans.

"Senator McCain is running for president to double down on George Bush's failed economic policies," Obama said.

"I am running to change them," he said. "And that's what will be a fundamental difference in this election when I am the Democratic nominee for president."

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