WASHINGTON - She's taking him to the Promised Land, her 17-hectare California estate.

But can  put Barack Obama in the Oval Office? That's the big question as the influential billionaire and talk-show queen holds her first political fundraiser this weekend amid rumours she'll assume a broader role in his Democratic presidential bid.

No one's saying just what she'll do, but there's speculation she might appear in TV ads and hit the campaign trail in support of the first African-American to have a decent shot at the White House.

Winfrey's been ranked the richest African-American of the 20th century. In June, Forbes magazine listed her as the world's most powerful celebrity, with earnings in the previous year of US$260 million.

But it's not her wealth that appeals most to Obama's campaign, already raising more money than Hillary Clinton but running second to her in polls of the eight Democratic candidates.

It's Winfrey's influence that counts more than anything.

Her talk show reaches 8.4 million viewers a day, many of them the critical female voters between 25 and 55 who tend to vote in large numbers.

She has a monthly magazine, a weekly newsletter and a website. She just launched a satellite radio channel. Her generous philanthropy is well known.

On her advice, people turn books into bestsellers. They buy other products she likes. They see the movies she approves.

Bloggers are wondering about a potential backlash, accusations that she's trying to buy the election and the unsavoury prospect of people blindly following her to the ballot box.

"Fundraising is fair game (but) becoming a spokesperson is forcing too much of your opinion down other's throats," said one blogger responding to a story about Oprah's clout. "She is, after all, still just an entertainer."

"I don't think Oprah can convince anyone directly to vote for Obama, but she can convince people to look closely at him and his policies and then decide for themselves," said another.

Many see Winfrey levelling the playing field by adding the kind of celebrity clout that Bill Clinton brings to his wife's campaign.

And they say it could help Obama with black voters suspicious of his upbringing, mostly in Hawaii, as the son of a white Kansas woman and a Kenyan father who returned to Africa.

Winfrey, who has never endorsed a political candidate before, has already sold out the $2,300 tickets to her bash Saturday on the grounds of her oceanside compound in Montecito, outside of Santa Barbara.

Rumoured guests include Hollywood stars like Halle Berry, John Travolta and Will Smith for an event expected to raise about $3 million.

Winfrey, who , first endorsed Obama on her show in May, saying he has the power to transform politics.

She met the rookie Illinois senator before he ran for Congress in 2004.

Now he's the only presidential candidate she'll have on her TV show, saying it would be "disingenuous" to invite anyone else.

Winfrey, who grew up dirt poor in Mississippi, has been called the most influential woman and black person of her generation by Life magazine.

And despite the odd controversy, she enjoys a wholesome reputation.

Even celebrity biographer Kitty Kelley, who specializes in digging up dirt, said she's having a hard time finding anything really nasty.

"So far, I don't see anything negative on this woman. I think she's a real icon."