But even his own advisers briefed this week that it was unlikely he would make an announcement on the day Mr Chirac turned 74, overshadowing what is likely to be the president's last birthday in power. Mr Chirac was once political mentor to Mr Sarkozy but their decade-old feud has become a drama that has gripped France and threatened to divide the party.
Mr Sarkozy had granted an interview to French regional newspapers that was not supposed to be published until this morning, but the left-leaning daily Libération, which has been critical of Mr Sarkozy, obtained a copy and released it on its website last night.

In the interview Mr Sarkozy was asked if he would run for president and replied: "My answer is yes."

He reasserted his plan for a "clean break" with the politics of the past, aimed at attracting voters deeply disillusioned with the political class after 12 years under Mr Chirac.

He said he wanted to break with the misguided idea in France that people could work less and earn more, and that welcoming immigrants meant they could be integrated. Echoing Ms Royal's promise to "listen" to the people, he said his ambition was "to create a new relationship with the French that rests on two words: confidence and respect".

Mr Sarkozy, 51, the son of a Hungarian aristocrat who studied law rather than attending the elitist postgraduate colleges that have shaped France's political class, has been eyeing the presidency for most of his career. Last night he described his decision to run as a "life choice".

He is best known for his tough stance on immigration and youth crime, and is angry that he is unable to shake off his pejorative comments that youths on France's rundown housing estates were "rabble" and the estates should be cleaned with a powerhose.

An economic liberal, he is aware that France's presidency hinges on international diplomacy and he has established himself, in contrast to Mr Chirac, as a "friend of America". But his tough stance on crime and immigration has led him to be accused, even by some in his own party, of fishing in the waters of the extreme right.

His biggest challenge in the elections next April and May is to establish himself as something radically different from the current ruling class, despite his role at the heart of the government for years. With no incumbent running for president for the first time in decades, he risks taking the flak of a disillusioned electorate.

The UMP party must formally nominate him at a party congress on January 14, but with 77% of party sympathisers' support, he is certain to win party backing.

But Mr Blair, who along with George Bush is among the most bullish of the Nato leaders about the prospects for Afghanistan, said: "I think there is a sense that this mission in Afghanistan is not yet won, but it is winnable and, indeed, we are winning."

Nato members agreed a messy and inconclusive compromise on reinforcements for British, American, Canadian and Dutch troops fighting in the south.

Other members have reluctantly promised to supply reinforcements in the event of "an emergency", but there was no agreement on a definition of emergency and no new promises of significantly more troops.

Officials predicted that the test of what constitutes an emergency would come when British or other forces face an onslaught similar to this summer's.

Mr Blair, who had been seeking a promise of 2,000 more troops, admitted that the British government had not secured all he had been hoping for from the summit. Nevertheless, he described the compromise as "significant progress".

But the Polish president, Lech Kaczynski, who has allied himself closely with Mr Bush and Mr Blair on Afghanistan and Iraq, said: "The summit did not have the character of a major breakthrough. Not all countries showed the same level of determination." The Polish government pledged several months ago to send an extra 1,000 troops, due to be deployed in January. The Czech Republic, Bulgaria, Spain and Macedonia announced at the summit that they would also send extra troops, but only modest numbers.

The French president, Jacques Chirac, said that, as a concession, he would allow a unit of French troops to operate outside Kabul. Mr Chirac, who was 74 yesterday, an occasion marked by other leaders with the presentation of a birthday cake, will also send planes and two helicopters, but no more troops to Afghanistan.

In an attempt to engage Afghanistan's neighbours, Pakistan and Iran, in trying to establish security, the summit agreed to Mr Chirac's plan, set out in an article in the Guardian on Tuesday, to set up a regional "contact group" to discuss ways of helping with the country's reconstruction. Nato's secretary general, Jaap de Hoop Scheffer, has been given the task of sounding out Iran, Pakistan and other neighbours about joining such a group.

The US, though agreeing in principle, may in the end decide against sitting round the table with the Iranians until they abandon their alleged nuclear weapons programme, or establish the group without an Iranian presence.

Mr de Hoop Scheffer echoed Mr Blair's upbeat assessment. "There is not the slightest reason for gloom over Afghanistan," he said. The mission "is winnable, it is being won, but not yet won".

In a separate development, Nato leaders yesterday took the controversial decision to invite Serbia and Bosnia to take the first step towards joining the transatlantic organisation, despite their failure to hand over wanted war criminals. The chief UN war crimes prosecutor, Carla del Ponte, expressed surprise and regret at the move.

Nato leaders also declared that a new 25,000-member rapid response force made up of specialist troops to deal with terrorist attacks, natural disasters and other major incidents, was ready for action after four years of preparation.

He added that he felt "a little ashamed" at Mr Bush's treatment of the Prime Minister, who had invested so much of his political capital in standing shoulder to shoulder with America after 9/11.

Speaking at an academic forum in Washington on Tuesday night, he answered a question from The Times, saying: "It was a done deal from the beginning, it was a onesided relationship that was entered into with open eyes . . . there was nothing. There was no payback, no sense of reciprocity."

His remarks brought calls from British politicians last night for the special relationship to be rethought, but also attracted scathing criticism from one close supporter of the Prime Minister.

Dr Myers had hard words for his own Administration's record in the Iraq war: "It's a bad time, let's face it. We have not only failed to do what we wanted to do in Iraq but we have greatly strained our relationship with [Britain]."

Dr Myers, a specialist in British politics, predicted that the tight bond between Mr Bush and Mr Blair would not be replicated in the future. "What I think and fear is that Britain will draw back from the US without moving closer to Europe. In that sense London's bridge is falling down."

The extraordinarily frank remarks will be seen as further evidence of the long-standing unease felt within some parts of the State Department over the direction of White House policy. They may also be an indication of the weakness of President Bush as he struggles to stop Iraq sliding into civil war and faces a Democrat-dominated Congress elected this month.

Sir Menzies Campbell, the Liberal Democrat leader, said: "These remarks reflect a real sense of distaste among thinking Americans for Mr Blair's apparent slavish support for President Bush . . . The special relationship needs to be rebalanced, rethought and renewed."

But Denis MacShane, Labour MP for Rotherham and a former Foreign Office minister, who supported the Iraq war, said: "After the Republican defeat in the midterm election, every little rat who feasted during the Bush years is now leaving the ship. I would respect this gentleman, who I have never heard of, if he had had the guts to make any of these points two or five years ago."

Last night Dr Myers, who is thought to have attended the discussions over the infamous Downing Street memo in 2002 before the Iraq war, was disowned by the State Department. Terry Davidson, a spokesman, said: "The US-UK relationship is indeed a special one. The US and the UK work together, along with our allies in Europe and across the world, on every issue imaginable. The views expressed by Mr Myers do not represent the views of the US Government. He was speaking as an academic, not as a representative of the State Department."

Privately, US officials are furious about the comments made by a man not even involved in the policymaking process, which can only rock relations at a time of high-wire tension in international diplomacy. Dr Myers himself was said to be considering early retirement.

He said on Tuesday that Mr Blair had been left "ruined for all time" by the Iraq war and that if he had "only read a book" on the last British invasion of Iraq in the 1920s, "he might have hesitated".