A new book by former US official David Kuo says President Bush's top political advisers privately ridiculed evangelical leaders, while publicly embracing them.

With just weeks to go before what promised to be highly competitive congressional elections, Republicans fear that they might lose the support of their evangelical Christian base.

Republicans are already concerned that the resignation of congressman Mark Foley over lewd e-mails he sent to teenage boys may have dissuaded some religious conservatives from turning out to vote. This book has the potential to make matters even worse.

The allegations made in Kuo's book have set alarm bells ringing in the White House, as it has denied the claims of the former official in the Faith-Based Initiatives programme.

The former official alleges senior aides to President Bush described the evangelical leaders in private as "nuts" and "goofy", while acknowledging their political use in securing election wins.

Kuo said that people in the White House referred to Pat Robertson as "insane," Jerry Falwell as "ridiculous", and James Dobson as having "to be controlled".

White House spokesman Tony Snow denied the accusations, saying: "These are people who are friends of many of us in the White House. You don't talk about friends that way."

"When [the President] talks about the Faith-Based Initiative, this is one of these things where he believes years and years down the road... this is going to be one of the signal accomplishments - harnessing the power of faith in dealing with some of the most intractable problems our society faces."

For the moment it is a short-term goal of keeping a Republican majority in Congress that seems most at threat.

Kuo is calling evangelical Christians to take a "fast" from politics. He said, "People are being manipulated. Good, well-meaning people are being told, 'Send your money to this Christian advocacy group or that.' And that's the answer. It's just not the answer. It's not the answer."

Kuo expects strong attacks from the White House and its supporters. He knows he will be viewed as a betrayer and that they will "go after him". He expects that he will be labeled as a "liberal" or an "idealist." But David Kuo says he is fine with that. He said, "I felt like I had to write this."