A clutch of candidates vying to be picked as vice-presidential running mate for Barack Obama or John McCain underwent final auditions yesterday, with loyal recitals on TV shows of official campaign talking points.

Mr Obama is widely expected to announce his choice ahead of next weekend's Democratic Convention in Denver and there has been fresh speculation that he is looking for someone with foreign policy experience who can reinforce his national security credentials.

Such a shortlist in the “veep-stakes” may be headed by Joe Biden, chairman of the Senate Foreign Relations Committee, who was in Georgia yesterday. Other names include John Kerry, the Democratic nominee in 2004 and a Vietnam veteran, as well as Bill Richardson, the New Mexico Governor and a former UN ambassador.

This weekend Mr Obama also flagged up a former Senate armed forces committee chairman Sam Nunn - a 69-year-old conservative Democrat - as someone he would rely on for advice in the White House. Alternatively, Mr Obama could opt for a running mate who shored up support in a key battleground. Senator Evan Bayh of Indiana - which narrowly voted Republican in 2004 - is a possibility. Yesterday he made a combative appearance on CBS's Face the Nation, criticising Mr McCain's “bellicose rhetoric” over Georgia and telling the Republicans to denounce a hostile book on Mr Obama.

The field for Mr McCain's vice-president appears even more crowded. A safe choice would be Tim Pawlenty, the youthful Governor of Minnesota, where the Republican convention is being staged next month and which is targeted as a gain from the Democrats. On CBS yesterday he said Americans would feel more secure with Mr McCain negotiating with Russia.

Another such candidate is Mitt Romney, a one-time rival to Mr McCain for the Republican nomination, who may help win Michigan, where his father was a popular governor. Mr McCain, however, is thought to be tempted by a more centrist figure, even Senator Joe Lieberman, the Democratic vice-presidential nominee in 2000, or former Pennsylvania governor Tom Ridge. Both are liberal on social policy, including abortion.

Abortion featured in a faith discussion hosted by Rick Warren, the Evangelical pastor, on Saturday, with Mr Obama and Mr McCain on the same platform for the first time in months. On whether the unborn have human rights, Mr Obama responded: “Whether you're looking at it from a theological or scientific perspective, answering that question with specificity is above my pay grade.”

Mr McCain, who has often been regarded with suspicion by social conservatives, won applause for declaring that human rights begin “at the moment of conception”. He appeared tearful while relating his experience with a guard as a prisoner of war in Vietnam who drew a cross in the sand on Christmas Day. Polls suggest he is beating Mr Obama by a margin of 67 per cent to 24 per cent among white, born-again or evangelical voters.

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