Hillary Clinton, widely expected to run for the White House her husband vacated six years ago, has received an unlikely and unwelcome vote of confidence from Dick Cheney, who said she could win the presidency in 2008.

Speaking in a blitz of conservative publicity yesterday, which Washington analysts said was designed to show Republican voters what could happen if the Democratic party performs well in the upcoming congressional elections, the Vice-President said the Senator from New York should not be underestimated.

"I think Hillary Clinton is a formidable candidate," Mr Cheney told Fox News. "I think she could win. I hope she doesn’t. I disagree with her on nearly all the issues, but nobody should underestimate her. She’s a very serious candidate for president."

Mr Cheney's comments are unlikely to alter his relationship with Mrs Clinton. She remains profoundly disliked by the Bush Administration and many Republican voters for her vitriolic attacks on the American Right during her husband's presidency and the contempt is mutual.

In August, during a row over a Democratic primary election, she said of the Vice-President: "I don't take anything he says seriously anymore".

Mr Cheney spoke at the end of a day that showed a visible increase in the intensity of the campaigning leading up to the midterm congressional elections on November 7. Pollsters have described the possibility of a "once-in-a-generation" election in which, riding a wave of dissatisfaction over the Iraq war and Republican corruption, the Democratic party retakes control of both houses of Congress.

A tent was pitched on the White House lawn to accommodate 42 radio broadcasters, mostly conservative, who conducted a day of interviews with senior members of the Bush Administration.

The Washington Post reported that Karl Rove, President Bush's senior political strategist, was on hand for a dozen interviews, while the Secretary of State, Condoleezza Rice, the Defence Secretary, Donald Rumsfeld, and the heads of Homeland Security, the Treasury and National Security all took to the airwaves on "Radio Day".

"It's mostly conservative talk," Tony Snow, the White House press secretary, told the newspaper in between doing 20 interviews himself. "This is a chance to talk to people and get heard."

Mr Cheney voiced his respect, and concern, for the prospects of Mrs Clinton during his own evening appearance on Fox News, the conservative-friendly cable news channel that has hosted President Bush and Mr Rove in recent days.

He also warned Republican voters about Nancy Pelosi, the leader of the Democratic party in the House of Representatives who would become speaker if control of the house changes hands in November.

"Nancy is not in sync with the vast majority of the American people," said Mr Cheney. "Nancy represents what I think is that side of the Democratic Party that has not been aggressive of and does not believe in a really robust, aggressive prosecution of the global war on terror."

He also referred to Barack Obama, the gifted but young Senator from Chicago, who is also thought to be weighing up a run for the White House in 2008: "Don’t know him well, met him a few times. I think at this stage, my initial take on him was, he’s been two years as a senator."

"I think people might want a little more experience than that, given the nature of the times we live in. But certainly, he’s an attractive candidate. If he decides to run, he’ll be a player on the Democratic side."

A report out today is expected to show that this year's election campaign will be the most expensive in American history. The Financial Times said that the midterm races will cost around $2.6 billion, with the Republicans spending $1.4 billion to the Democratic party's $1.2 billion.

The Centre for Responsive Politics, a non-partisan group that tracks campaign contributions, will report that political action committees (Pac's), which are formed by businesses, unions and campaign groups with specific agendas, are expected for the first time to spend more than $1 billion supporting their favoured candidates.

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