Washington - John McCain's right-hand man hit a raw nerve on Monday when he said another terrorist attack on US soil would prove a "big advantage" to the Republican nominee's general election chances.

    The comments by Charlie Black, who is arguably Mr McCain's most experienced adviser, put into words what many Republicans and Democrats have privately been stating for months.

    Mr Black, 60, who is a veteran of every Republican presidential campaign since the 1980s and served in the Reagan and Bush Senior administrations, immediately apologised for his remarks, which were published in an interview with Fortune Magazine.

    Mr McCain, whom opinion polls show is trailing Barack Obama, his Democratic rival, by between six and 15 points, said: "I cannot imagine why he would say it. I strenuously disagree ... It's not true. I have worked tirelessly since 9/11 to prevent another terrorist attack on America."

    The Obama campaign said: "The fact that John McCain's top adviser says that a terrorist attack on American soil would be a 'big advantage' for their political campaign is a complete disgrace and is exactly the kind of politics that needs to change."

    The controversy arrived at a bad moment for the McCain campaign, which has come under increasing fire from otherwise friendly Republicans for its alleged amateurism. Critics say it has sent out mixed signals about Mr McCain's political direction and shown a lack of "message discipline".

    For example, last week the campaign put out a televised advertisement stressing Mr McCain's credentials on global warming on the same day that he gave a speech in Houston calling for a lifting of the moratorium on offshore drilling.

    Republican consultants also worry the campaign has not invested in on-the-ground operations in swing states, such as Ohio, to nearly the degree as George W. Bush did in 2004 or as has the Obama campaign.

    Although many commentators may agree with Mr Black, his remarks are likely to result in calls for Mr McCain to remove him. Democrats have accused Mr McCain of hypocrisy for portraying himself as a political reformer while relying on several prominent working and former lobbyists for advice and fundraising.

    As one of those lobbyists Mr Black - who headed the lobbying firm BKSH until he resigned in March - has also been targeted by groups that allege hypocrisy in Mr McCain's critical stance on such firms. Some McCain staff, including Tom Loeffler, a senior fundraiser who previously lobbied for Saudi Arabia's government, have resigned from the campaign.

    MoveOn.org, the liberal activist group, recently launched a television advertisement calling for Mr McCain to fire Mr Black because of his lobbying work for foreign dictators, including Joseph Savimibi of Angola and Ferdinand Marcos of the Philippines.

    According to recent opinion polls Mr Obama has a clear lead over Mr McCain on almost every domestic issue. However, both Mr McCain and the Republican party in general continue to hold an edge on national security and terrorism. Electoral analysts believe a McCain victory in November would likely arise from an election dominated by national security concerns.