The quarter-century hold that “values voters” from the Christian Right have had over the Republican Party is being directly challenged by Rudy Giuliani’s presidential bid.

Having spent months failing to appease his antiabortion critics, the former New York Mayor and front-runner for the Republican nomination has decided to adopt a high-risk strategy by tackling them head on.

Yesterday Mr Giuliani underlined his “pro-choice” stance of supporting abortion rights while speaking at Houston Baptist University, while also addressing his key campaign themes of taxes and terrorism.

The change of tack became apparent this week in Huntsville, Alabama, where he was questioned over abortion and fresh disclosures about a past donation to the Planned Parenthood organisation.

“Ultimately, there has to be a right to choose,” he said. Asked whether the party’s conservative base would nominate a candidate with such views for president, he replied: “That’s up to Republicans – I guess we are going to find out.”

The new strategy follows his agonisingly ambivalent answer at last week’s Republican presidential debate in California, where, surrounded by nine unequivocally antiabortion candidates, Mr Giuliani appeared deeply uneasy about the issue.

Asked about the prospects of overturning the 1973 Roe v Wade Supreme Court decision that legalised abortion in all US states, he replied with a rhetorical shrug. “It would be OK to repeal,” he said. “Or it would be OK also if a strict constructionist judge viewed it as a precedent.” His previous references to “strict constructionist judges” – who have a literal interpretation of the US Constitution – had been seen as code for supporting the repeal of Roe v Wade, which critics say conflates the right to privacy with a right to abortion.

But Mr Giuliani’s new approach suggested that he might nominate Supreme Court justices who viewed the 34-year-old ruling as too ingrained in precedent to reverse.

Although public opinion is broadly in favour of Roe v Wade, the issue has become a test of faith among Republicans, who have nominated antiabortion presidential candidates since 1976.

This week opponents pounced on the chance to split Mr Giuliani from the Republican base. John McCain said: “I think it’s one of the fundamental principles of a conservative to have respect and commitment to the dignity of human life, both the born and unborn.”

Mr McCain’s strategists have long since argued that the more Republican voters find out about Mr Giuliani’s policies as mayor of the liberal city of New York, the less inclined they will be to support him.

That record includes support for gun control and gay rights.

Opinion polls indicate that Mr Giuliani’s status as the Republican front-runner has been eroded in recent weeks, with four out of six national surveys giving a lead of less than 10 per cent over Mr McCain, who is also becoming stronger in Iowa, New Hampshire and South Carolina, the first three states to select presidential candidates.

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