Republican Newt Gingrich is so unimpressed with his own party's 'chaotic' line-up of candidates to replace President Bush in the 2008 elections that he has threatened to make a dramatic late entry into the race.

The 64-year-old former Speaker of the House spent last week making speeches attacking Bush's handling of Iraq and the 'war on terror' and calling for 'big ideas' that would unite a disillusioned America behind a strong rival to Clinton.

He called General David Petraeus's report to Congress on the military surge in Iraq 'wholly inadequate', adding: 'The gap between where we are and where we should be is so large it seems almost impossible to explain.'

Gingrich plans to criss-cross the country in the next few weeks holding 'workshops' with politicians and fundraisers before assessing his chances of winning the Republican nomination over the leading candidates who have already declared: former New York mayor and narrow favourite Rudy Giuliani, film actor and former senator Fred Thompson, war veteran John McCain and millionaire Mormon Mitt Romney.

Republican sympathies are scattered, while Democrats are lining up far more clearly behind Clinton. She has about 40 per cent of support, with Barack Obama and John Edwards trailing by a significant margin.

At a small breakfast gathering in a Washington hotel overlooking the White House, Gingrich told The Observer he will decide next month on a run for president and will jump into the race if 'there is a large enough vacuum on our side, if people get frightened enough of the prospect of President Clinton - and if I have enough money.'

Gingrich is a darling of the right who shot to fame when he spearheaded a massive mid-term electoral victory for the Republicans in 1994. They took control of the House of Representatives, against all odds, for the first time in 40 years and made Gingrich their star.

He spent the next four years undercutting Bill Clinton's policies and shifting his party to the right, and became instrumental in forcing the President's impeachment over the Monica Lewinsky affair. He later admitted that he had cheated on both his first and second wife and was having his own affair with a younger woman - now his third wife - at the same time Clinton was romancing Lewinsky in the Oval Office.

Gingrich was forced out by his own party when his viciously negative campaign in the 1998 mid-term elections saw his party lose vital seats.

He left Congress in 1999, but his name is burnt into the memories of both friends and enemies, and the prospect of him coming back to haunt Hillary is causing a huge buzz in Washington and beyond.

'There is a tremendous amount of goodwill towards Newt among grassroots conservatives and he still remains one of the leading thinkers and ideas people in the Republican party. And he would be popular with swing voters. I would like to see him in this process,' said Saul Anuzis, chairman of the Michigan Republican Party.

Gingrich's big ideas include more tax cuts, bringing market forces to bear even more strongly in US healthcare, and creating a military and economic blockade of Iran aimed at crippling the country and strangling its influence.

He takes an interest in environmental politics: he has written a book on green issues that comes out next month. However, rather than taxing and regulating polluters, he wants to reduce carbon emissions and global warming with 'cash prizes', tax incentives and ecological entrepreneurialism. 'If you had a $1bn prize for inventing the first mass-produced hydrogen-powered car, it would happen pretty quickly,' he said.

Democrats claim to be salivating at the prospect of a Gingrich candidacy. 'Hillary and the Democrats would love Newt Gingrich as the Republican nominee. We'd pick up all the swing voters,' said Bob Mulholland, a member of the Democratic National Committee and a veteran Bill Clinton adviser. 'He is not presidential material. He is a flame-thrower, but Newt's time has gone. And his personal life is not in shape.'

Gingrich admits he was weak when he committed adultery, but claims he was not a hypocrite because he never lied to Congress.

Anuzis said he did not think Gingrich's multiple marriages and infidelities would bother the majority of Republicans these days: 'Bill Clinton changed the definition of politics and nowadays it's more about policies and less about whether someone inhaled or got a divorce. He set a new level of the bar and it would be difficult to find another politician who could wriggle below that.'

All candidates wishing to enter the Utah primary are obliged to have paid their entry fees by 15 October. Either way, Gingrich will need to have made a decision by then.