John McCain has begun to draw up a list of potential running mates as he seeks to transform his ragged primary operation into a general election machine capable of beating Barack Obama or Hillary Clinton in November.

With his Democratic rivals still embroiled in their nomination fight, Mr McCain is building up a national campaign staff, has installed a new fundraising team and this week began a quest to introduce himself to voters across America with a biographical “Service to America” tour.

Having wrapped up the Republican nomination, he is also mapping out a longer-term strategy to appeal to independents and moderate Democrats — a key to his past political fortunes — while uniting a fractious Republican party and mollifying rebellious conservatives; a tough challenge.

The Democratic battle offers Mr McCain the luxury of a squabbling opposition and the time to build up his national profile, but his aides concede it also risks keeping him out of the spotlight. After his visits to Europe, Iraq and the Middle East last month, the Arizona senator's “biographical tour” this week is the latest attempt to stay in the headlines, and the first stage in his plan to sell himself to America.

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Fresh polls suggest that, in the short term, the scrap between Mr Obama and Mrs Clinton is helping Mr McCain, and increasingly threatens the eventual Democratic nominee. The Republican is slightly ahead of both in head-to-head match-ups, and appears to be gaining ground among independents and even some Democrats.

He also has the space to give prolonged consideration to a running mate, often the first important decision a nominee makes. Conservatives, long suspicious of Mr McCain, hope that he will choose one of their ilk. It will be a significant factor in his deliberations, but other credentials, such as age — Mr McCain, 71, would be the oldest US president to be sworn in — will also be important.

On paper Mitt Romney, Mr McCain's former presidential rival, is a strong contender. Conservatives like him and he is considered strong on the economy, the number one issue for voters and a vulnerability for Mr McCain. Yet they are far from close personally.

Several governors will also make the list. Charlie Crist of Florida is popular in the Sunshine State, a key battleground, but is considered suspect on abortion by the Right. Minnesota's Tim Pawlenty is young, at 47, was an early backer of Mr McCain and is a fiscally experienced steward of another swing state. Mark Sanford, 47, of South Carolina, is another possibility and is well liked by the party's base.

Rudy Giuliani, the former Mayor of New York, will be considered but his moderate social views are anathema to many in the party. Mike Huckabee, another former rival for the nomination, is strong among social conservatives, but that may be a drawback for a general election audience. Another popular choice among conservatives would be Rob Portman, 52, a fiscal hawk, former Ohio congressman - a critical swing state - and President Bush's former budget director.

Mr McCain's tour is taking him to places that highlight his military heritage — his father and grandfather were both admirals — as well as his own career as a naval pilot that led to 5 years as a prisoner in Vietnam, when he was tortured frequently.

At the US Naval Academy in Annapolis — an institution where Mr McCain graduated fifth from bottom of his class — he continued his theme this week of describing his journey from a brash, unruly, arrogant, ill-disciplined and self-centred youth to one who rejoiced in service.

“The most important thing I learnt here was that to sustain my self- respect for a lifetime, it would be necessary for me to have the honour of serving something greater than my self-interest,” Mr McCain said.

Later this spring Mr McCain will begin a nationwide tour that will bring him to places most Republicans ignore, such as black neighbourhoods, and recently Democratic states.

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