Mr McCain also implicitly criticised President Bush for not using the Sept 11 attacks in 2001 to call Americans to unite in a common national purpose. -- PHOTO: AFP

The party's presidential pick also mused on the lessons of his rebellious youth, as he sought to frame his life story as a history of self sacrifice and military service, the culmination of which would be the presidency.

'The point is, I'm not running on the Bush presidency, I'm running on my own service to the country, my own record in the House of Representatives and the United States Senate and my vision for the future,' Mr McCain told ABC television. 'Now we'll have lots of time to portray that, and I'm doing that now.'

Mr McCain, 71, has been a fierce supporter of the Iraq war, though challenged the Bush administration's past management of the conflict, and admits his fortunes could be tied to the way the war develops over the next nine months.

In an appearance at his old boarding school outside Washington, Mr McCain also implicitly criticised President Bush for not using the Sept 11 attacks in 2001 to call Americans to unite in a common national purpose.

'I think after 9/11 we made a mistake, we made a mistake in telling Americans to take a trip, to go shopping, I think we had an opportunity to call Americans to service,' he said.

VIDEO US Campaign Candidates Spar (1:57)

New rationale for electing Republicans
Mr McCain is attempting to provide a new rationale for electing Republicans, despite popular fatigue over the war, and his party's besmirched record of sound economic management.

Last week, in a major foreign policy address, Mr McCain laid out a robust national security policy, but offered olive branches to US allies alienated by the go-it-alone approach of the Bush administration.

He is also stressing his support for a comprehensive international effort to tackle global warming, and for closing the Guantanamo 'war on terror' camp - two areas of policy in which President Bush has infuriated US allies.

At Episcopal High School in Alexandria, from which he graduated in 1954, Mr McCain walked down memory lane as part of an attempt to reintroduce himself to American voters, even as the Democratic presidential race rages on.

The presumptive Republican nominee also attempted to play down perceptions that his urbane exterior masks a smouldering temper.

'I arrived here a pretty rambunctious boy, with a little bit of a chip on my shoulder,' said Mr McCain.

'As a young man, I would respond aggressively and sometimes irresponsibly to anyone whom I perceived to have questioned my sense of honour and self-respect,' said Mr McCain, who has also alluded to his heroism as a Vietnam war prisoner this week.

'In all candour, as an adult I've been known to forget occasionally the discretion expected of a person of my years and station when I believe I've been accorded a lack of respect I did not deserve,' Mr McCain said.

'But I believe if my detractors had known me at Episcopal they might marvel at the self-restraint and mellowness I developed as an adult,' he joked.

On Monday, Mr McCain got into a slanging match over Iraq with Democratic pace-setter Barack Obama, arguing the Illinois senator 'does not understand the fundamental elements of national security and warfare.' Senator Obama retorted that McCain wanted a 'permanent occupation in Iraq' and that like President Bush, he had 'no clear definition of success' there.

On Tuesday, Senator Obama returned to his theme, saying it was not Mr McCain's biography that he faulted 'it's his policies.' as he campaigned in Pennsylvania, which holds the next Democratic nominating contest on April 22. -- AFP